BENSON OUHC Series User guide

1
INSTALLATION & SERVICING MANUAL FOR
BENSON OUH² OIL UNIT HEATER
WARNINGS
Benson equipment must be installed and maintained in accordance with the current OFTEC
Regulations for oil fired products. Due account should also be taken of any obligations
arising from the Health and Safety at Works Act 1974 or relevant codes of practice. In
addition the installation must be carried out in accordance with the current IEE wiring
regulations (BS 7671), BS 6896: Industrial & Commercial) and any other relevant British
Standards and Codes of Practice by a qualified installer. All external wiring MUST comply
with the current IEE wiring regulations.
Technical Support:
Tel: [phone]
Email: [email protected]
AmbiRad Limited, Fens Pool Avenue, Brierley Hill, West Midlands, DY5 1QA

2
1 Compliance Notices …………………………………....………..…..…………. 4
1.1 Certificates of Conformity ………………………………..…………..…. 5
1.2 General Product Information …………………………………….…………. 5
1.3 General Requirements ……...……………………………………...………. 5
1.4 Delivery & Pre inspection …………………………………………….…. 6
1.5 Warranty ……………………..…….………………………………………. 6
2 Location & Positioning …………………….………………..…………..…………. 7
2.1 Fuel Supply - General …………..…..……………...………………………. 7
2.2 Fuel ……………...……………………………..……………...……………. 8
2.3 Storage Tank ……………………..…………………….……………….. 8
2.4 Single Pipe System (Gravity Fed) ….…………..………………...………. 9
2.5 Two Pipe System …………………….…………...…………………… 9
2.6 Pressurised Ring Main System ….…………..………………...………. 9
2.7 Pipework and Fittings …………………….…………...…………………… 9
2.8 Electrical Supply ……………...……………………………..………………. 11
2.9 Air Supply ……………………..……………………….……………………. 11
2.10 Warm Air Circulation …………………………………...……...…………. 14
2.11 Flue System …….…………………………...………………..….……. 15
3 Installation …………………………………………………...…….…….…………. 16
3.1 Mounting Heights ………………...……………………...……………. 16
3.2 Heater Mounting …………………………………………………..……...…. 16
3.3 Minimum Clearances ……………………………………...………………. 16
3.4 Flue Installation ……………………………..……..………….……...……. 16
3.5 Oil Installation & Connection ….……………..……………..……...………. 17
3.6 Electrical Installation & Connection….……………………..……...………. 17
3.7 Heater Control Installation ……………………………….………………. 17
4 Commissioning ……………..…………………………...…………….…….……. 18
4.1 Pre test …………………………………………………...…..…..………. 18
4.2 Ignition ……………………………………………………….…..………. 18
4.3 Air Delivery System …………………………………....…...…..….……. 20
4.4 Hand Over …………………………………………………...….…...………. 20
5 Servicing …………………………………………………...…………..…………. 21
5.1 Planned Servicing …………………………………....………..………. 21
5.2 Servicing procedure Major Components ….……………………...………. 21
5.3 Service Re commissioning ….…………………………………...………. 23
6 Fault Diagnosis By Flow Chart ………….………………...…….……...……. 24
7 Wiring Diagrams ……………………………………………………...……………. 27
8 Technical Data …………………………………………………...………………. 35
8.1 Reference Documents Standards & Codes of Practice ...……...…… 36
9 Parts Listing …………………………………...………………..……………………. 37
10 Dimensional Drawings ………………………………….………...………………. 35
Contents

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~ C O N T E N T S ~
S E C T I O N 1
1.0 Compliance Notices 4
1.1 Certificates of Conformity 5
1.2 General Product Information 5
1.3 General Requirements 5
1.4 Delivery & Pre-installation Checks 6
1.5 Warranty 6
2.0 Location & Positioning 7
2.1 Gas Supply 9
2.2 Electrical Supply 9
2.3 Air Supply 9
2.4 Minimum Space Requirements 12
2.5 Air Distribution System 12
2.6 Flue System 13
2.7 Flue Installation 13
3.0 Installation 16
3.1 Packaging & Siting 16
3.2 Flooring 16
3.3 Minimum Clearances 16
3.4 Assembly 16
3.5 Gas Installation and Connection 17
3.6 Electrical Installation & Connection 17
3.7 Air Distribution Installation 17
3.8 Warm Air Registers 17
3.9 Heater Control Installation 18
4.0 Commissioning 18
4.1 Pre-Test 18
4.2 Ignition 19
4.3 Air Delivery System 21
4.4 Hand Over 21
5.0 Servicing 22
5.1 Planned Servicing 22
5.2 Servicing Procedure - Major Component Parts 22
5.3 Servicing - Re-commissioning 25
6.0 Fault Diagnosis By Flow Charts 26
7.0 Wiring Diagrams by Model and Burner Type 28
8.0 Technical Data Net Efficiency Calculations 35
8.1 Benson Cabinet Range Data 36
9.0 Reference Documents Standards, Codes of Practice 39
9.1 Parts Listing 40
11 User Instructions …………………………………………………………...………. 40
11.1 Commissioning/hand over ……………………………….……….……... 40
11.2 Servicing ……………………………….…………………………..…….… 40
11.3 Start up procedure ……………………………….…………….….……. 40
11.4 Stop procedure ……………………………….……………………………. 40
11.5 Shutdown procedure ……………………………….……………...……... 40
11.6 Ventilation only ……………………………….…………………..….…..... 40
11.7 Lockout situations ……………………………….…...………..………. 40
Illustrations
1 Oil Systems ………………………………………………………...……………. 10
2 Turbulator positions …………….…………………………………………………. 23
Any reference made to Laws, Standards, Directives, Codes of Practice or other
recommendations governing the application and installation of heating appliances and
which may be referred to in Brochures, Specifications, Quotations, and Installation,
Operation and Maintenance manuals is done so for information and guidance purposes only
and should only be considered valid at the time of the publication. Benson Heating cannot
be held responsible from any matters arising from the revision to or introduction of new
Laws, Standards, Directives, Codes of Practice or other recommendations.
Bio fuel statement.
All our oil fired heater products are configured for
use on both Class D light distillate fuel oil.
As a result of recent changes made to European
legislation regarding the specification of class D
heating oil to allow for the inclusion of 7% FAME
(Fatty Acid Methyl Ester) i.e. bio fuel and
effective from early 2011, all oil fired air heater
products and installations maybe affected.
From April 2011 all our oil fired unit heaters
will be fitted with Riello burners which are bio
fuel compatible for blends up to 10%.
Please note that the use of bio fuels may give rise
to a number of installation issues, to both new
and existing plant which could affect the warranty
of the burner. We recommend that you familiarise
yourself with current information from both the
burner manufacturer Riello and OFTEC.

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1.0 Compliance notices
The following information is relevant to the
Benson Oil Fired Unit Heater range (OUHA)
and (OUHC) manufactured by Benson
Heating. These heaters are manufactured
within a strictly controlled quality
environment within the parameters of ISO
9001.
The Benson OUHA (C) has been tested and
assessed for compliance with the following
European Directives.
Machinery Directive: (2006/42/EC)
Low Voltage Directive: (2006/95/EC)
Electromagnetic Compatibility Directive:
(2004/108/EC)
Product Liability Directive: (85/374/EEC)
The manufacturer has taken reasonable and
practical steps to ensure that Benson Unit
Heaters are safe and without risk when
properly used. These heaters should
therefore only be used in the manner and
purpose for which they were intended, and
in accordance with the recommendations
detailed herewith.
The heaters have been designed,
manufactured, assembled, inspected, and
tested, with safety and quality in mind, there
are certain basic precautions which the
installer and user should be aware of, and
they are strongly advised to read the
appropriate sections of the information pack
accompanying the heater, prior to
installation or use.
Benson Heating supports all new products
being supplied to their customers with a
comprehensive information pack; this clearly
defines mandatory instructions for the safe
installation, use, and maintenance, of the
appliance (s).
Where proprietary items are incorporated
into Benson Heating products, detailed
information and instructions are also
provided as part of the information pack.
It is the responsibility of the installer, owner,
user, or hirer, of such products supplied by
Benson Heating, to ensure that they are
familiar with the appropriate information/
manuals, supplied by the manufacturer, and
that they are suitably aware of the purpose
of the manuals and the safety instructions.
In addition, operators must be suitably
trained in the use of the appliance so as to
ensure its continued safe and efficient use.
Benson Heating has a commitment to
continuous improvement, and therefore
reserves the right to amend or change the
specification of the Unit Heater range
subject to compliance with the appropriate
European, National, and Local regulations.
Contained within the text of the manual, the
words 'Caution' and 'Warning' are used to
highlight certain points.
Caution is used when failure to follow or
implement the instruction (s) can lead to
premature failure or damage to the heater or
its component parts.
Warning is used when failure to heed or
implement the instruction (s) can lead to not
only component damage, but also to a
hazardous situation being created where
there is a risk of personal injury.
The Benson OUHA(C) Range conform to
the following harmonized standards:
BS EN 292-1
Safety of Machinery - Basic Concepts,
General Principles for Design Basic
terminology, methodology
BS EN 292-2
Safety of Machinery - Basic Concepts,
General Principles for Design Technical
Principles and Specifications
BS EN 60204-1
Safety of Machinery - Electrical Equipment
for Machines Specification for General
Requirements
BS EN 60335-1
Safety of Household and Similar Electrical
Appliances General Requirements
BS EN 55014
Limits and methods of measurement of radio
disturbance characteristics of electrical
motor-operated and thermal appliances for

5
household and similar purposes, electrical
tools and similar electric apparatus
BS EN 50165
Electrical Equipment of non-electric heating
appliances for household and similar
purposes, safety requirements
1.1 Certificates of conformity
Certificates are available from the Quality
Control Department at Benson Heating.
1.2 General product information
The Benson OUH unit heater models have
an output range from 30kW to 100kW. Each
heater must be connected to its own
individual open flue.
Each heater is fitted with a forced draught
burner which has been test fired and pre-set
prior to despatch. The safety functions of the
burner are by way of a fully sequential
control box fitted to the burner.
Note
Neither asbestos nor soft soldered joints are
used in the construction or manufacture of
the Benson range of Unit Heaters. The
materials selected for use can withstand the
mechanical, chemical, and thermal stresses
which they will be subject to during foreseen
normal use when installed in accordance
with the manufacturers recommendations.
1.3 General requirements
Caution
Ensure that the fuel supply is in accordance
with the manufacturer's recommendations
and is as stated on the appliance data plate.
Installation, commissioning, and
servicing must only be carried out by
appropriately qualified and competent
persons.
Warning
Unauthorised modifications to the appliance,
or departure from the manufacturers
guidance on intended use, or, installation
contrary to the manufacturers
recommendations may constitute a hazard.
Note
To ignore the warning and caution notices,
and to ignore the advice from the
manufacturer on installation, commissioning,
servicing, or use, will jeopardise any
applicable warranty, moreover, such a
situation could also compromise the safe
and efficient running of the appliance itself,
and thereby constitute a hazard.
The installation of the appliance must meet
all the relevant European, national, and local
criteria. (See sections 3 and 9).
Prior to installation the following points
should be considered;
a) The position of the heater for the optimum
efficient distribution and circulation of warm
air.
b) The position of the heater relative to the
route of the flue.
c) The position of the heater relative to the
supply of fuel.
d) The position of the heater relative to the
electrical services, and if appropriate, any
additional controls.
e) The position of the heater relative to the
supply of fresh air.
f) The position of the heater relative to
service and maintenance requirements.
Caution
The heater must not be installed within an
area where the conditions are unsuitable,
e.g. where the atmosphere is highly
corrosive, has a high degree of salinity, or
where high wind velocities may affect burner
operation. Suitable protection should be
provided for the appliance when it is located
in a position where it may be susceptible to
external mechanical damage from; for
example, fork lift trucks, overhead cranes
etc.

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1.4 Delivery and pre-installation
checks
The heater is supplied wrapped in heavy
duty protective polythene. On receipt of the
heater, the following checks should be
carried out;
a) The model is as per order
b) That it is undamaged
c) That it is suitable for the fuel supply
d) That it is suitable for the electrical supply
If any of these points are not satisfied then
contact should be made with the Sales
Office at Benson Heating as soon as
possible by Telephoning 01384 489200. In
the case of claims for damage, this must be
signed for as damaged and be reported in
writing within 24 hours of delivery, in order to
comply with insurance criteria.
1.5 Warranty
The heater is supplied with a 1 year parts
and labour warranty and a further year on all
parts excluding consumable’ s.
In addition to this there is also a 10 year
time related warranty on the combustion
chamber.
The warranty commences from the date of
dispatch from the manufacturer, and is
subject to the terms detailed within the
Benson Heating 'conditions of business'.
Note (i)
The warranty may be invalidated if -
a) The installation is not in accordance with
the general requirements of this manual.
b) The flue arrangement and air supply for
the heater are not in accordance with the
manufacturers recommendations, codes of
practice, or similar standards.
c) Air flow through the heater is not in
accordance with the manufacturers technical
specifications.
d) Internal wiring on the heater has been
tampered with or unauthorised service/
repairs undertaken.
e) The main electrical supply input to the
heater has been interrupted during the
heating mode.
f) The heater has been subject to and
affected by the ingress of water in any form.
g) The heater is not operated at the rating(s)
laid down in the manufacturers technical
specifications.
h) The heater has not been operated or
used within the normal scope of its intended
application.
i) The manufacturer's recommended
minimum service requirements have not
been complied with.
Note (ii)
All warranty claims must contain the
following information to enable processing to
take place;
(1) Heater model.
(2) Heater serial number
(3) Order reference/date of order, together
with full installation details (name and
address)
(4) Details or symptoms of fault
(5) Installers name and address.
Faulty parts must be returned to the Benson
Spares Department, the address of which is
provided at the rear of this manual. Any
such parts will undergo inspection to verify
the claim.
Replacement parts supplied prior to this may
be charged, and a credit supplied upon
subsequent validation of the warranty claim.
Consumable items are specifically not
included within the scope of the warranty.
Note (iii)
Notification is required immediately a fault is
suspected.
The manufacturer will not accept
responsibility for any additional damage that
has been caused, expense incurred, or
consequential loss resulting from any failure
of the heater(s).

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Warning
All of the basic criteria must be satisfied
prior to commencing installation and
commissioning, additionally, the Unit Heater
must be positioned and installed so as to
comply with all the relevant standards and
guide lines (see section 9.0), as well as
meeting National and Local Fire Regulations
and Insurance criteria, especially if it is
proposed that the heater is to be installed
within a special risk area (e.g. proximity to
where petrol engined vehicles are stored or
parked, where cellulose spraying takes
place, where woodworking machinery is
operated, etc,).
Indirect fired heaters must not be located in
hazardous areas, however, it is permissible
for the heater to supply air to such areas.
The heater must not be installed within an
environment where there is a high
concentration of chlorides, fluorides, salts, or
other aggressive or volatile chemicals/
compounds. Nor should the heater be
positioned where high winds or draughts
could adversely affect the burner.
The heater must be installed so that it is
level. Supports for the heater must be
sufficiently robust to withstand the weight of
the heater and any ancillary equipment. Any
combustible material adjacent to the heater
or flue system must be so placed or shielded
so that its surface temperature does not
exceed 65°C
The location chosen for the heater must
allow for the fitting of an effective flue
system.
The location must also allow for adequate
clearance for the air supply, return air
circulation, oil supply, electrical supply,
whilst also providing good and safe working
access.
Suspended free blowing Unit Heaters are at
their most effective when located as close to
the working area as possible. However care
should be exercised to avoid directing the
discharged air directly onto the occupants of
the area to be heated.
Where the passage of cold air causes
problems (e.g by entrances, loading bays
etc) it is considered favourable if the heater
is positioned so as to discharge towards or
across the cold air source from a distance
from 1.5m - 6m dependent upon the size of
the entrance and the air throw
characteristics of the heater.
On exposed walls heaters should be
positioned so as to discharge towards, or
along the length of the exposed wall. In
areas where it is proposed that more than
one heater is to be installed, a general
scheme of circulation should be drawn up
and maintained, thereby offering the best
heat distribution.
Air pressure within the area heated and the
outside air pressure must remain the same,
factors influencing this would be the
presence of extraction systems, ventilation
systems, and various types of process plant.
OUHA 60-100 models can be installed to
allow the fans to work in opposite directions.
This enables the heater to be installed
centrally in the area to be heated and allows
warm air to be discharged to both the front
and rear of the heater.
2.1 Fuel supply - general
The Benson range of oil fired heaters are all
manufactured and pre-set for use with 35
second gas oil delivered to the burner via a
suitable piped system from the oil storage
tank.
Galvanised or plastic pipe work and
fittings must not be used. (see BS 5410
Part 1 1997)
The constraints of the application will, to a
large extent, determine whether it is
preferable to use a single pipe gravity feed
system, or whether the two pipe pumped
system is more appropriate.
Where more than one appliance is to share
a common supply it will be necessary to use
a pressurised ring main system.
2.0 Location/positioning

8
All pipe work must be constructed and
installed so that it does not permit the
ingress of air.
The construction, size, and position of the oil
storage tank must take account of the
current regulations, as well as suiting the
requirements of the installation.
Caution
On pumped systems always check that the
pump is correctly set up prior to running, and
always ensure that valves are open allowing
a free flow of oil through the system.
2.2 Fuel
In order to promote trouble free operating it
is necessary that the oil within the storage
tank and oil line does not fall below the cold
filter plugging point (cfpp), in this country
and with class D fuel (also referred to as gas
oil). The critical temperature is -4°C for this
summer grade.
The cfpp critical temperature for the winter
grade is -12°C. If summer grade fuel is
stored for winter use in areas prone to
severe frosts and low temperatures it will be
necessary to insulate or even heat the
supply tank and pipe work.
Note
The fuel supplier should be contacted prior
to installation so that any requirements
concerning delivery, transport, storage and
use can be addressed before work
commences.
Warning
The pump pressure must not exceed a
maximum of 0.4 bar, this is because beyond
this point gas is liberated from the oil.
The heaters are set for single pipe
operation. A bypass plug is provided
separate with the burner for conversion to
two pipe see Riello manual.
2.3 Storage tank
An externally painted steel storage tank to
BS 799 part 5 1987 or a medium density
polyethylene oil tank OFTEC certified to
OFS T-100 may be used. Local, national,
European and fire regulations must also be
complied with and must include:
A fuel level gauge (not made from glass) a
vent pipe with a diameter greater than that
of the filler and featuring a weatherproof
termination.
A sludge valve.
An outlet valve situated at the opposite end
of the tank to the sludge valve.
A filler pipe connection situated at the
opposite end to the outlet valve.
The size of the storage tank must take
account of the estimated consumption and
any quantity price breaks offered by the oil
supplier.
It is preferable to install the tank outside,
however, if this is not practicable and the
tank has to be installed indoors advice must
be sought about its siting, especially so far
as fire regulations are concerned.
If a separate fire resistant chamber cannot
be provided for indoor installations, a
catchment pit with a capacity ten percent
greater than that of the storage tank must be
provided
Storage tanks can if necessary be sited on a
roof, but this is subject to special regulations
as well as local authority approval and
compliance with fire regulations, reference
to BS 5410 part 2 1978 & part 1 1997 is
strongly suggested.
It is advisable to leave the tank unpainted on
the inside, but to paint the outside with a
proprietary grade of anti-corrosive paint.
A galvanised or open topped tank is strictly
not allowed.
All oil storage tanks require a bund
The Control of Pollution Regulation (Oil
Storage) 2001 should be consulted prior to
installation.

9
2.4 Single pipe system (gravity feed)
For installations where the oil tank is 200mm
or more above the level of the fuel pump the
principle of gravity feed may be used.
The draw off point for the supply to the
burner must not be positioned any lower
than 100mm above the bottom of the tank.
Where a return valve is fitted this must be
tamper proof to prevent inadvertent
operation.
Caution
If the valve is closed when the pump is
running the oil pressure can be increased
sufficiently so as to cause damage to the
seals within the pump.
The return oil should preferably be
discharged through an elbow onto a tank
plate situated within the tank, this should be
positioned so as not to introduce air or air
bubbles into the draw off pipe.
2.5 Two pipe system
This is used where the oil storage tank is
lower than the pump.
Access for the fuel feed to the burner should
be via a suitable tapping made in the top of
the tank, and the fuel feed pipe should
extend to not less than 100mm above the
bottom of the tank.
A none return valve with a metal to metal
seat should be fitted, especially if the return
pipe work is terminated at a level above the
draw off tube. The non- return valve must be
removable for service and maintenance
purposes, and the return pipe from the
pump must therefore be extended down into
the tank to the same level as the suction
pipe.
The presence of a tamper proof isolating
valve fitted within the return pipe is only
required if there is a risk that oil will siphon
out of the tank if the return pipe is
disconnected at the pump during
maintenance or servicing and if the none
return valve has been omitted.
Caution
The Deareator must be fitted the burner
side of the inlet fuel filter
Maximum lift should not exceed 3.5 metres,
and the vacuum should not exceed 0.4 bar.
Each heater must have a separate fuel
supply.
Note
It is strongly recommended that the separate
manual concerning the operational details of
the burner supplied with the heater as part
of the information package is studied prior to
installation.
2.6 Pressurised ring main system
This system is used to supply a number of
units from a common storage tank.
A booster pump is used to provide the
pressure to push the oil around the ring
main and back to the tank.
Pressure reducing valves should be fitted on
the delivery pipe to each heater to ensure
that the pressure at the burner pump is less
than 6 psi.
Caution
The internal by-pass plug must be removed
from the burner pump when used in a
pressurised ring main application.
2.7 Pipe work and fittings
Caution
Galvanised or plastic pipe work and
fittings must not be used. (see BS 5410
Part 1 1997)
All joints must be sealed properly, if
necessary using PTFE tape or other
approved sealing media.
The pipe work must be effectively sealed so
as to prevent the ingress of air.
It is advisable to check all pipe work prior to
installation to ensure that there is no loose
debris or scale present.

10
BURNER
H
m
0
0.5
1.0
1.5
2.0
3.0
3.5
I.D.
8mm
35.0
30.0
25.0
20.0
15.0
8.0
6.0
I.D.
10mm
100.0
100.0
100.0
90.0
70.0
30.0
20.0
Maximum
4 metres
H
H
Priming the pump: Start the burner and await priming.
Should lock-out occur prior to arrival of the fuel, wait at least 20 seconds
before repeating the operation.
This solution, however, is less saf e than the previous one, due to
possibility of leakage of the valve.
Should, however, the return line terminate over the fuel level,
a non return valve is es sential.
The return line should terminate within the oil tankat the same level
as the suction line; in this case a non return valve is not required.
The pump suction should not exceed a maximum of 4 metres.
Bey on d th is li mit gas i s re lea sed fr om t he o il .
Typical Fuel Layout
BURNER
H
The pump suction must not exceed 4 metres;
beyond this value the pump becomes noisy.
The return valve must te rmin ate at the same level
as the foot valve, otherwise the pump may
become air locked.
1 GATE VALVE
2 IN-LINE FILTER
3 PUMP
4 RELIEF VALVE
5 PRESSURE GAUGE
6 PRESSURE REDUCING VALVE
7 RETURN TO TANK
12
3
45
66
7

11
Black iron pipes can be hammered to assist
in the removal of these contaminants.
Note
The oil feed to each heater must be fitted
with a fire check valve and isolating valve.
The fire check valve must be operated by
way of a fusible link positioned so that it is
above the burner.
Note
Any waste oil or sludge must be
disposed of correctly.
Never dispose of it by dumping or
tipping it down drains or into
watercourses where ground water can
become polluted and environmental
damage caused.
2.8 Electrical supply
Wiring external to the unit heater must be
installed in accordance with any local,
national, and European regulations, as well
as meeting the appropriate requirements of
IEE regulations.
The means of connection to the main
electrical supply must allow for complete
electrical isolation of the heater, furthermore,
in the case of a unit wired for a three phase
supply, the supply should only be used to
serve the heater itself and no other plant or
equipment. The position of the isolation
switch must be such that it is adjacent to the
heater and easily accessible at all times. In
addition, the isolator itself must have a
contact separation of not less than 3mm.(as
per BS5991 clause 20.2).
All connections must be checked to ensure
that they are secure, and free from
corrosion.
Terminals and connections should also be
checked to ensure that no stray strands are
bridging terminals.
Electrical continuity should also be checked.
Cables, conduit, and fittings that are used to
make the connection between the isolator
and the heater must conform to the
appropriate IEE regulations.
All heaters are supplied fused and
pre-wired, all must be earthed.
The Control fuse ratings are detailed on the
appliance data plate.
Warning
Ensure that the electric and oil supplies are
turned off before any electrical work is
carried out on the heater.
Ensure that wiring cannot make contact with
any surfaces liable to be subject to high
temperatures or where the insulation of the
wiring could be impaired as a result of such
contact.
Final connections for any additional external
controls must be completed on site, and
must be carried out according to IEE
regulations.
Separate user information is provided for the
time control unit and the burner, and forms
part of the product information pack which
accompanies every heater when
despatched.
Caution
The main electrical supply must not be
switched off or disconnected as a method
for stopping the heater, the exception to this
is in an emergency, or during servicing,
when the heat exchanger has been allowed
to cool sufficiently to prevent any damage
from occurring. Claims for damage will not
be considered if they have resulted from
incorrect wiring or the incorrect use of the
heater.
Always ensure that the appropriate
personal protective equipment is used.
2.9 Air Supply
Provision must be made for the existence of
an air supply in order to satisfy both
combustion and ventilation criteria.
It is a requirement that the area where the
air heater is located must have a permanent

12
air vent of negligible resistance direct to the
outside air.
Such air vents must be positioned so as not
to become blocked or flooded, nor should
they be placed so as to introduce
undesirable matter (e.g. flammable, volatile,
or aggressive chemicals/compounds or
potentially hazardous or harmful
substances) either direct from the outside, or
through their proximity to an adjacent
extraction system.
Note It is strongly recommended that BS
6230 is referred to for further information
concerning ventilation requirements
Where mechanical ventilation is used it is a
requirement that the inlet is of the
mechanical type, and the outlet is either
mechanical or natural.
2.9.1 Heaters installed within the
heated space.
Where heaters are installed within the space
to be heated (i.e. not a plant room or
enclosure) then:
Combustion air or heater related ventilation
air will not be required if -
• The design air change rate of the
heated space is 0.5 air changes per
hour or greater or
• The design air change rate may be
satisfied by natural infiltration or by
mechanical ventilation
Combustion and General ventilation will be
required if -
• The design air change rate of the
heated space is less than 0.5 air
changes per hour or
• Where the heated space has an air
change rate of less than 0.5 air
changes per hour then it will be
necessary to provide either natural
ventilation openings to the heated
space (section 2.9.1.1 refers) or the
mechanical ventilation of the heated
space (section 2.9.1.2. refers)
2.9.1.1 Natural Ventilation Openings
to the Heated Space.
If the heated space design air change rate is
less than 0.5 air changes per hour then
provision for low level natural ventilation
openings will only be necessary.
The minimum free area of the low level
natural ventilation opening shall be:
• 2cm2for each kW of rated heat input
The low level natural ventilation opening
should be situated on an external wall and
be within 1000 mm of floor level for natural
gas and ideally at floor level for l.p.g gas
installations but in any event no higher than
250 mm.
The table in the next column provides
specific data for each heater model as -
2.9.1.2 Mechanical Ventilation to the
Heated Space.
In the event that the heated space has a
design air change of less than 0.5 air
changes per hour and that installer prefers
to mechanically ventilate the heated space
rather than provide ventilation openings then
-
• The heated space needs to be
mechanically ventilated so that the
design air change is 0.5 air changes or
greater.
Model
Minimum Free Area of
ventilation opening
High Level Low Level
cm2cm2
30 None 68
40 None 88
60 None 128
70 None 166
90 None 192
100 None 230

13
• It is a requirement that the mechanical
ventilation shall be of the ‘input’ type
with either natural or mechanical
extraction.
• Systems of mechanical extraction with
a natural inlet shall not be used.
• It is necessary to provide an automatic
means to safely inhibit heater(s)
operation should mechanical air
supply fail for any reason.
2.9.2. Heaters Installed within a Plant
Room or Enclosure.
A plant room means a room housing the
heater plant and probably other items of
building service plant and would generally
have generous space for maintenance.
An enclosure is where the heater is installed
within a compartment or confined area
where space is limited.
Where heaters are installed within a plant
room or enclosure then provision for both
combustion air and air for general ventilation
will be required by means of high and low
level ventilation openings (sections 2.3.2.1
refers to plant room applications and
sections 2.3.2.2 refers to enclosure
applications).
Alternatively the plant room or enclosure
may be mechanically ventilated (section
2.3.2.3 refers).
2.9.2.1 Natural Ventilation Openings
to Plant Rooms
For plant room applications the minimum
free area of ventilation opening shall be:
• At high level 2 cm2for each kW of
rated heat input.
• At low level 4 cm2for each kW of rated
heat input.
The high level ventilation opening should be
sited on an external wall and positioned as
high as is practical and always within the top
15% of the wall height.
The low level natural ventilation opening
should be situated on an external wall and
be within 1000 mm of floor level for natural
gas and ideally at floor level for l.p.g gas
installations but in any event no higher than
250 mm.
The table below provides specific data for
each heater model as -
2.9.2.2 Natural Ventilation Openings
to Enclosures
For enclosure applications the minimum free
area of ventilation opening shall be:
• At high level 5 cm2for each kW of
rated heat input.
• At low level 10 cm2 for each kW of
rated heat input.
The high level ventilation opening should be
sited on an external wall and positioned as
high as is practical and always within the top
15% of the wall height
The low level natural ventilation opening
should be situated on an external wall and
be within 1000 mm of floor level for natural
gas and ideally at floor level for l.p.g gas
installations but in any event no higher than
250 mm.
The table in the next column provides
specific data for each heater model as -
Model
Minimum Free Area of
ventilation opening
High Level Low Level
cm2cm2
30 68 134
40 88 176
60 128 258
70 166 332
90 192 384
100 230 460

14
2.9.2.3 Mechanical Ventilation to a
Plant Room or Enclosure.
In the event that the installer prefers to
mechanically ventilate the plant room or
enclosure rather than provide ventilation
openings then -
• The plant room or enclosure needs to
be mechanically ventilated at the rate
of 4.14 m3/h of fresh air per kW or
rated heat input.
• It is a requirement that the mechanical
ventilation shall be of the ’input’ type
with either natural or mechanical
extraction. Where mechanical
extraction is selected then the
extraction rate should be 5%-10% less
than the input rate.
• Systems of mechanical extraction with
a natural inlet shall not be used.
• It is necessary to provide an automatic
means to safely inhibit heater(s)
operation should mechanical air
supply fail for any reason.
The table opposite provides specific data for
each heater model as -
2.10 Warm Air Circulation
The air heater should be positioned to
enable maximum circulation of discharged
warm air within the area to be heated, whilst
taking account of personnel within the area,
sources of cold air ingress, and obstructions.
Ensure louvres are adjusted outwards
and ensure blades are not resonating
The air temperature rise on passing the heat
exchanger is typically around 340°C
A full and unobstructed return air path to the
air heater must be provided (see 2.9 Air
Supply).
Where the heater is positioned to deliver
blown air through an opening in a wall,
return air intakes should be located so that
they cannot become blocked. Similarly these
intakes must be positioned so as not to draw
in odours, fumes, hazardous vapours or
particles.
Model
Minimum Free Area of
ventilation opening
High Level Low Level
cm2cm2
30 170 340
40 220 440
60 320 640
70 415 830
90 480 960
100 575 1150
MODEL Mechanical Ventilation Rate for
Plant Room or
Enclosure
M3/h
30 141
40 182
60 265
70 344
90 397
100 476

15
2.11 Flue system.
Warning
It is essential that the products of
combustion are flued to the outside of the
building. Each heater must have its own
separate flue, with a flue diameter of not
less than is detailed in this manual.
The minimum vertical length of flue must not
be less than 1m. The number of bends
should be kept to a minimum.
It is strongly advised that BS 5854; 1980,
and BS 5440; parts 1 and 2, are used as
consultative documents when considering
flue requirements.
Care should be taken to ensure that the flue
terminal is not situated in a high-pressure
area, the proximity of buildings and other
obstacles which will influence this must be
taken into account, preferably at the design
stage.
Provision must be made for the
disconnection of the flue for inspection and
service requirements, and it is strongly
advised that where bends are fitted
inspection covers are included.
Flue should be supported at intervals not
exceeding 1.8 mtrs
The materials from which the flue is
constructed must be non-combustible,
resistant to internal and external corrosion,
and be capable of withstanding the stresses
and loadings associated with normal use.
When designing the flue system the
prevention of the formation and entrapment
of condensation must be a key
consideration.
Twin wall or insulated systems are
recommended, as they tend to inhibit the
formation of condensates.
Where condensation is unavoidable traps
should be included to encourage the
condensates to flow freely to a point from
which they may be released, preferably into
a gully.
The condensate pipe from the flue to the
disposal point must be made from corrosion
resistant pipe of not less than the internal
diameter of the drain pipe.
If the flue passes through a wall, ceiling, or
roof made from combustible material then it
has to be sleeved so as to provide a
minimum of a 25mm void between the
exterior of the flue and the internal wall of
the sleeve. The maximum permitted
temperature of any adjacent combustible
material is 65°C.
The position of the flue and its terminal
should be such that it does not impair the
combustion process. It should terminate in
an exposed position so as to allow the
escape and dissipation of flue gases without
risk of their re-entering the property through
windows, ventilation ports, etc.
The flue should extend to at least 1m above
the height of any object within 3.5m of the
terminal.
Flue terminals should be fitted on all flues,
the terminal must be of the approved type,
and have outlet grilles on all sides giving a
total free area of at least double that of the
flue.
Caution
It is imperative that the flue should be
properly sealed where it passes through the
roof, this can best be achieved by using the
approved method of roof flashing plate and
cravat.
Note
It should be noted that claims made under
warranty and attributed to the ingress of
water may not be considered especially if an
approved method of sealing has not been
used, or if the design of the flue has not
made provision for possible condensation
problems.

16
3.1 Installation Mounting Heights
OUHA models
The Heater must be installed within the
mounting heights indicated below in metres.
The following clearances in mm must be
observed *when suspended:
3.2 Heater Mounting
The heater and flue must be adequately
supported by one of the following methods;
a) Suspension by steel drop rods or straps
from the M10 fixing points located on top of
the heater. These must be of sufficient
strength to safely carry the weight of the unit
and ancillary equipment. The straps may
only drop vertically to eyebolts, if used; I.E.
They must not be joined to the eyebolt at an
angle to the vertical, and eyebolts if used
should be of an approved type.
b) OUH heaters can be mounted on
specifically designed cantilever wall or
vertical stanchion brackets which locate
directly to the four M10 fixings on the heater
casing.
Alternatively OUHA or OUHC units can be
mounted on cantilever type wall brackets
however consideration must be given to
ensure that the bracket is large enough to
support the heater whilst providing the
necessary clearances.
In either case the installer should ensure
that the wall wall fixings or other support
medium is capable of supporting the weight
c) On a level non-combustible surface
capable of adequately supporting the weight
of the unit and ancillary equipment .
3.3 Minimum clearances
The following minimum clearances (in
millimeters) are recommended when
installing the heater.
3.4 Flue Installation
An integral flue spigot is fitted to all unit
Heaters thereby allowing the flue to connect
directly to the heater.
The design of the flue must ensure that it
can be disconnected to allow for cleaning
and servicing, furthermore, all of the flue
section joint sockets must face upwards,
and the seal between the sections achieved
through mechanical joints or through the use
of approved caulking string and grout.
It is strongly advised that BS 5854 and BS
5440 parts 1 and 2 are referred to.
Where condensation is likely to be a
problem provision should be made
preferably at the design stage.
3.0 Installation
Model Size
OUHA Min Max
30 2.0 2.7
40 2.0 2.7
60 2.4 3.0
70 2.4 3.5
90 2.5 3.5
100 2.4 3.5
Model 30 40 60 70 90 100
Above 300
Below* 300
RHS 680 810
LHS 250
Rear
OUHA 400 560
Rear
OUHC 200

17
3.5 Oil Installation/connection
The oil tank must be positioned so that there
is a fall of 7.5mm (+/- 2.5mm) for every
30mm away from the outlet and towards the
sludge/drain valve, which must be sited at
the lowest point in the tank. If the tank is
positioned on supports then there must be
an adequate protective layer between tank
and support to prevent damage or
deterioration through corrosion. It is strongly
suggested that reference is made to BS
5410 ; part 2 ; 1978.
It is also suggested that the installer is
familiar with the detail and requirements
contained within sections 2.1 through to
section 2.6 of this manual prior to
commencing installation.
Warning
Prolonged exposure and contact with Gas
Oil can result in the natural oils being
removed from the skin, sensitisation can
result in dermatitis.
Always ensure that the appropriate personal
protective equipment is used.
3.6 Electrical Installation/connection
Benson unit heaters are only available in
230V 50Hz 1PH.
It is recommended that reference is made to
the wiring diagrams contained within section
7 of this manual prior to installation or
connection to the supply. The electrical
supply must be as specified and suitable for
the heater, and must be run within conduit to
a point adjacent to the heater, and be
terminated to provide an isolation point that
will prevent remote or inadvertent activation.
Cables, conduit, and fittings that are used to
make the connection between the isolator
and the heater must conform to the
appropriate IEE regulations.
All heaters are supplied fused and
pre-wired, all must be earthed.
Final connections for any additional external
controls must be completed on site, and
must be carried out according to IEE
regulations.
Separate user information is provided for the
time control unit and the burner, and forms
part of the product information pack which
accompanies every heater when
despatched.
Warning
Always isolate from mains electrical supply
before commencing work on the heater.
Always ensure that the appropriate personal
protective equipment is used.
3.7 Heater Control Installation
Warning
Isolate heater from mains before
undertaking any electrical work.
Unless specified all Unit Heaters are
manufactured and supplied with a remote
controllers are available to be wired back to
the heater.
Refer to Controller instruction manual for full
installation details.
See section 7.0 for individual wiring
diagrams.

18
Note:
It is a requirement that only suitably
qualified and competent personnel are
allowed to undertake the commissioning
of the heater.
It is also strongly recommended that
prior to commissioning the engineer
familiarises himself with; the information
contained within the information pack
that accompanies the heater, the heater
itself, and with the specific requirements
of the installation/application.
Warning
All Unit Heaters undergo a rigorous test
programme prior to being despatched, whilst
such a programme does involve pre-
commissioning and setting up the heater to
operate efficiently and well within its
designed operational limits, this does not
mean that on site commissioning is less
important than might otherwise be the case.
The idiosyncrasies of each installation can
only ever be allowed for, through the use of
thorough on site commissioning carried out
by trained and experienced personnel
equipped with the correct tools and
apparatus.
Note
It is strongly recommended that equipment
used for the sampling and analysis of flue
gases is accurate to within +/- 0.1% and
maintained so that it is regularly calibrated.
4.1 Commissioning - Pretest
Check to ensure electrical safety, and
inspect and check the oil installation, testing
for leaks.
(a) Ensure that the electrical supply is turned
off.
(b) Ensure that the oil supply is turned off.
(c) Check that all panels and fasteners are
secure and in place.
(d) Check that the heater is installed
correctly and that the support is adequate.
(e) Ensure that warm air delivery outlets are
open.
(f) Check that fan is free to rotate and the
guards are in place.
(g) Ensure that the flue is secure,
adequately supported, and that the various
joints are properly sealed.
(h) Check that there is provision for flue gas
sampling and that this sample point can be
plugged and sealed after commissioning.
(i) Remove cover from fan limit stat assy
check that the fan and limit stat settings
have not been disturbed.
(j) Ensure that the burner is securely
attached to the heater.
(k) Test for electrical earth continuity
between the heater, oil pipe work, and
mains supply.
(l) Turn on main electrical supply.
(m) Enable fan on via controller by selecting
‘Fan only’; ‘Vent only’; ‘Vent/Manual’.*
(* dependent on control type supplied. Refer
to individual controller operating manual.)
(n) Check to ensure burner is off but power
remains to the fan. The fan will start
enabling fan direction etc to be verified.
Reset Fan on/standby switch to off.
(o) Set room thermostat and time clock to
'demand' positions.
(p) Turn mains electrical supply to off,
replace and secure lower louvered panel
covering fan and motor assembly.
4.2 Commissioning - Ignition
Note
It is strongly recommended that the separate
manual concerning the operational details of
the burner supplied with the heater as part
of the information package is studied prior to
commissioning.
Time intervals within the ignition sequence
will vary slightly from one model to another.
Warning
Do not proceed with commissioning unless
all the criteria detailed have been satisfied.
(a) Ensure the electrical supply is turned off.
(b) Ensure that the Oil supply is turned off.
(c) Turn on main electrical supply.
(d) Enable burner via controller by selecting
‘Heat’ (Relay 2); ‘Heat On’; ‘Heat/Auto’. *
(* dependent on control type supplied. Refer
4.0 Commissioning

19
to individual controller operating manual.)
(e) Select 'on' position for heater on/standby
switch.
(f) Check for the following burner sequence
1 <5s Combustion air damper actuated,
burner fan motor initiates purge
cycle...
2 <40s Solenoid valve opens ignition
transformer provides spark for
burner ignition...
-------- E I T H E R --------
3 >15s Ignition failure caused by oil
starvation resulting in burner
lock-out/shut-down...
(g) Set heater on/standby switch to standby
position
(h) Attach oil manifold (bleed screw and
pressure gauge)
(i) Open oil supply valves and bleed air from
pipe work and adjust burner oil pressure as
per detailed in burner manual (section B)
(j) Repeat steps c,e,f.
----------- O R ----------
3 >15s Pilot ignition... Burner ignition...
4 <20s Burner ignition cycle complete
Warning
If burner ignition is not satisfactorily
accomplished, commissioning must not
proceed until the reason or fault has been
identified and rectified, if necessary by
reference to the separate burner information
or to section 6 of this manual.
(k) Repeat steps 4.2 c,a,
(l) Repeat steps 4.2 d,e,f, allowing the
heater to reach thermal equilibrium.
(m) Adjust room thermostat to its highest
setting, and allow the heater to continue to
fire.
(n) Gradually reduce the temperature setting
on the room thermostat until the burner
shuts down, (@ < ambient and then
gradually increase the temperature setting
on the thermostat until heat is called for, (@
> ambient) and the burner automatically re-
fires.
(o) Re-set time clock to a minimum off
period, checking that the burner shuts down,
and then automatically re-lights once the
minimum off period has elapsed (Separate
information on the time clock is contained
within the information package supplied with
the heater).
(p) Check limit stat by isolating fan control
circuit
The time between the fan stopping and
burner shut down should be noted.
If the time interval between fan stop and
burner shut down is greater than 2 minutes
Check settings on fan and limit stat are
correct.
(q) Undertake flue gas analysis using
approved and calibrated analysing
equipment recording data on the
commissioning card, ie, CO, CO2, net and
gross flue temperatures.
Record burner oil pump pressure, ambient
temperature, barometric pressure, and
smoke reading (0 - 1 Baccarach scale).
Note (i)
The burner air and oil pressure settings
should be only very finely adjusted to
achieve a CO2reading of 12.5% (+/- 0.5%).
Note (ii)
The gross efficiency must be approximately
80 % sample taken at 1m above the flue
spigot point.
Note (iii)
All Unit Heaters are test fired and pre-
commissioned as part of the manufacturing
process, if however, during on site
commissioning the data are found to be not
in accordance with the manufacturers data,
then the following action is recommended.
* Re-check all readings and calculations.
* Adjust burner as per manufacturers
instructions.
* Consult Benson Heating Technical
Department.
(r) Complete commissioning card and
provide operating instructions for the user,
high-light the fact that the manufacturer
recommends that in the interests of safety
and efficiency the heater is serviced on a
regular basis only by qualified and
competent persons.

20
The completed commissioning card must be
returned to Benson Heating Service
Department immediately after the
satisfactory completion of commissioning,
failure to do so can invalidate any
subsequent warranty claim.
(s) Set all controls to the requirements of the
user.
(t) Final adjustment for the direction of the
air flow from the heater should be made.
4.3 Commissioning - air delivery
system
Final adjustment of the air louvres are
adjusted outwards and ensure blades are
not resonating.
Caution
On ducted applications it is necessary that
the system is balanced in order to optimise
the efficiency of the heater and the air
distribution and delivery system Failure to
balance the system can result in fan motor
overloading and premature component
failure, it can also result in an inefficient
heating/ventilation system.
(a) Check that the amount of fan produced
air volume is in accordance with the heater
specification, if the volume is too great the
fan can be overloaded. Ensure that the
running current is as per that stated on the
heater data plate.
Alternatively, the static pressure should be
measured at the start of the ductwork to
confirm that it is within the permissible
tolerance.
(b) If the current drawn is greater than the
stated running current, in most probability
this will be caused by insufficient static
pressure within the ductwork, in which case
system resistance should be increased
through the introduction of a damper placed
as close to the start of the ductwork as
possible, thereby resulting in a reduction in
drawn current.
The damper should be adjusted until the
current is in accordance with that stated on
the data plate.
(c) If the current drawn is too low the duct
outlet grilles will require opening to reduce
static pressure and increase air volume, if
this is not the case overheat cut outs can be
caused.
4.4 Commissioning - hand over
(a) Upon full and satisfactory completion of
commissioning, a record of commissioning
information (contact, date, etc) should be left
with the heater, a copy of which must also
be forwarded to Benson Heating Service
Department.
(b) The commissioning engineer must
ensure that the user is familiar with the safe
and efficient use of the heater, detailing the
function of all controls, and main
components.
(c) The user should be made aware of the
following in particular:
(i) Lighting, shutdown, and operational
information.
(ii) Safety features, data plate, and labelling.
(iii) The requirement for regular inspection -
especially if the heater is within a more
demanding environment - and the need for
regular servicing carried out by competent
and qualified persons.
(d) Section C 'User Instructions' should be
left with the customer upon satisfactory
completion of the commissioning and
hand-over.