HTP SSU-10DB Operating instructions

120 Braley Rd. P.O. Box 429 East Freetown, MA 02717-0429 www.htproducts.com
LP- 351b REV. 2.3.14
Drain Back Tank
INSTALLATION
OPERATION
MAINTENANCE
TROUBLESHOOTING
Models*
SSU-10DB / 15DB / 20DB / 30DB
40DB / 60DB / 80DB
SSU-10DBX / 15DBX / 20DBX
40DBX / 60DBX / 80DBX
*“X” following the model number denotes models with internal heat exchanger
NOTICE: HTP reserves the right to make product changes or updates without notice and will not be held liable for typographical errors
in literature.
NOTE TO CONSUMER: PLEASE KEEP ALL INSTRUCTIONS FOR FUTURE REFERENCE.
This manual must only be used by a qualified heating installer/service technician. Read all instructions in this manual before installing.
Perform steps in the order given. Failure to comply could result in substantial property damage, severe personal injury, or death.

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The following defined terms are used throughout this manual to bring attention to the presence of hazards of various risk
levels or to important information concerning the product.
DANGER indicates an imminently hazardous situation which, if not avoided, will result in death or serious injury.
WARNING indicates a potentially hazardous situation which, if not avoided, could result in death or serious injury.
CAUTION indicates a potentially hazardous situation which, if not avoided, may result in minor or moderate injury.
CAUTION used without the safety alert symbol indicates a potentially hazardous situation which, if not avoided, may result in property
damage.
FOREWORD
This manual is intended to be used in conjunction with other literature provided with the solar water heating system. This includes all
related control information. It is important that this manual, all other documents included with this system, and additional publications
including Solar Water Heating System Design and Installation Guidelines, be reviewed in their entirety before beginning any work.
Installation should be made in accordance with the regulations of the local code authorities and utility companies which pertain to this
type of water heating equipment.
FOR THE INSTALLER
INSTALLATION OR SERVICE OF THIS SOLAR PRODUCT IS REQUIRED TO BE PERFORMED BY LICENSED PROFESSIONALS
WHERE SOLAR, PLUMBING, AND ELECTRICAL WORK IS REQUIRED.
The installer should be guided by the instructions furnished with the tank, local codes and utility company requirements. Preference
should be given to codes and requirements where they differ from the furnished instructions. Always use the latest edition of codes.
Additional publications which should guide the installer include:
Local, state, provincial, and national codes, laws, regulations and ordinances.
Solar Water Heating System Design and Installation Guidelines, SRCC OG-300, from Solar Rating and Certification Corporation, 1679
Clearlake Road, Cocoa, FL 32922-5703.
Code for the Installation of Heat Producing Appliances (latest version), is available from American Insurance Association, 85 John
Street, New York, NY 11038.
The latest version of the National Electrical Code, NFPA No. 70.
In Canada, refer to Canadian Electrical Code C 22.1, from Canadian Standards Association, 5060 Spectrum Way, Suite 100,
Mississauga, Ontario, Canada L4W 5N6.
TABLE OF CONTENTS
INTRODUCTION..........................................................................................................................................................................3
PART 1 - GENERAL SAFETY INFORMATION...........................................................................................................................4
A. PRECAUTIONS..........................................................................................................................................................................4
B. LOCAL INSTALLATION REGULATION .....................................................................................................................................5

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LP- 351b REV. 2.3.14
C. CHEMICAL VAPOR CORROSION ............................................................................................................................................5
D. INSULATION BLANKETS..........................................................................................................................................................5
E. DOMESTIC HOT WATER SCALD PREVENTION.....................................................................................................................5
F. FREEZE PROTECTION.............................................................................................................................................................5
PART 2 - GENERAL INFORMATION..........................................................................................................................................6
A. PIPING .......................................................................................................................................................................................6
B. SIZING THE DRAIN BACK TANK..............................................................................................................................................6
PART 3 - SPECIFICATIONS .......................................................................................................................................................7
PART 4 - INSTALLATION ...........................................................................................................................................................9
A. DRAIN BACK TANK LOCATION................................................................................................................................................9
B. SYSTEM PIPING AND PLUMBING............................................................................................................................................9
C. INSTALLATION OF THE DRAIN BACK TANK ..........................................................................................................................9
1. DRAIN BACK TANKS WITHOUT HEAT EXCHANGERS ............................................................................................................10
2. DRAIN BACK TANKS WITH HEAT EXCHANGERS....................................................................................................................10
D. SOLAR SYSTEM PUMP..........................................................................................................................................................10
E. ELECTRICAL INSTALLATION.................................................................................................................................................10
F. DRAIN BACK TANK WITH BACK UP GAS WATER HEATER DETAIL...................................................................................11
G. DRAIN BACK TANK WITH BOILER AND INDIRECT WATER HEATER DETAIL ...................................................................12
H. DRAIN BACK TANK WITH HEAT EXCHANGER.....................................................................................................................13
PART 5 - FLUID QUALITY........................................................................................................................................................14
PART 6 –INSTALLING THE SOLAR DRAIN BACK TANK SIGHT GLASS............................................................................14
PART 7 - STARTING YOUR DRAIN BACK SYSTEM...............................................................................................................15
A. FILL THE DRAIN BACK RESERVOIR .....................................................................................................................................15
B. START-UP PROCEDURE........................................................................................................................................................15
PART 8 - SERVICE/MAINTENANCE PROCEDURES..............................................................................................................15
A. SHUT DOWN PROCEDURE....................................................................................................................................................15
B. DRAINING THE DRAIN BACK RESERVOIR...........................................................................................................................15
C. ROUTINE MAINTENANCE ......................................................................................................................................................15
D. VACATION PROCEDURES.....................................................................................................................................................15
PART 9 - TROUBLESHOOTING...............................................................................................................................................16
A. LEAKS......................................................................................................................................................................................16
B. OTHER PROBLEMS................................................................................................................................................................16
INSTALLATION AND MAINTENANCE NOTES...............................................................................................................................16
HTP CUSTOMER INSTALLATION RECORD FORM ......................................................................................................................17
INTRODUCTION
Drain back tanks are designed to allow solar collectors and related piping to drain heat transfer fluid into the drain back reservoir when
not in use.
Drain back systems are versatile: ideally suited for both cold and warm regions. The drain back process protects solar system
components from both freezing and overheating, and saves power by shutting down the solar system when there is no longer a

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LP- 351b REV. 2.3.14
demand for hot water. Drain back systems have fewer components than pressurized systems, making drain back systems easier to
use, service, and maintain.
Your drain back tank may come with an internal heat exchanger (for use with a storage tank), or without a heat exchanger (for use with
either a solar water heater with an internal heat exchanger or a storage tank with an external plate and frame heat exchanger).
Job site conditions will require your installation contractor to supply some or all of the following:
Plumbing Connections
Piping and Insulation
Valves Between the Existing Domestic Water System and the Drain Back Solar System
NOTE: Solar system performance and efficiency varies with factors such as: household hot water load, ambient air temperature,
collector/roof pitch, collector orientation, and seasonal intensity.
NOTE: Failure to follow the procedures described in this manual WILL VOID the warranty.
PART 1 - GENERAL SAFETY INFORMATION
INSTALLER –Read all instructions in this manual before installing. Perform steps in the order given.
USER –This manual is for use only by a qualified installer/service technician. Refer to user’s information manual for your reference.
Have this heater serviced/inspected by a qualified service technician annually.
FAILURE TO ADHERE TO THE GUIDELINES ON THIS PAGE CAN RESULT IN SUBSTANTIAL PROPERTY DAMAGE, SEVERE
PERSONAL INJURY, OR DEATH.
A. PRECAUTIONS
NOTE: OBTAIN ALL APPLICABLE PERMITS AND OBEY ALL LOCAL CODES.
NOTE: Install all system components and piping in such a manner that does not reduce the performance of any fire rated assembly.
Any claims for damage or shortage in shipment must be filed immediately against the transportation company by the consignee.
Improper installation or use may result in property damage. Such damage IS NOT covered by warranty.
If any system component(s) is/are exposed to the following, do not operate until the affected component(s) has/have been inspected by
a qualified serviceman.
1. FIRE
2. DAMAGE
3. SUBMERSION IN WATER
Ensure there are no low points or dips in sloped non-vertical supply and return pipe runs from the solar collectors to the drain back tank.
Low points and improperly designed solar piping can trap water and possibly rupture in freezing weather. Pitch non-vertical piping ¼”
per foot towards the drain back tank to facilitate proper drainage, and take care to properly layout piping to ensure there are no low
points.
In addition, the drain back tank and solar storage tank must be protected from freezing temperatures. Care must be taken when filling
the system to avoid overfilling and exposing pipes to a freezing condition.
NOTE: HTP DOES NOT WARRANT THE DRAIN BACK TANK AGAINST FREEZE RELATED DAMAGE.
ALL PIPING AND PLUMBING CONNECTIONS SHOULD BE MADE WITH COPPER PIPE ONLY. No less than ¾” I.D. copper tube of
the type meeting local codes must be used for piping. Pipe runs must be solidly attached with proper clamping methods. Soldered
connections should be secured with 95/5 lead-free solder. Use only copper pipe rated for 250oF minimum on both the collector return
and supply piping.

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LP- 351b REV. 2.3.14
B. LOCAL INSTALLATION REGULATION
Installation of this solar water heater may be governed by individual local rules and regulations for this type of product, which must be
observed. Always use the latest edition of codes. The installation, adjustment, service, and maintenance of the solar water heater must
be done by a licensed professional who is qualified and experienced in the installation, service, and maintenance of solar hot water
systems.
C. CHEMICAL VAPOR CORROSION
NOTE: DAMAGE TO THE SOLAR WATER TANK, COLLECTOR, OR RELATED COMPONENTS CAUSED BY EXPOSURE TO
CORROSIVE VAPORS IS NOT COVERED BY WARRANTY. The limited warranty is voided when failure of water tank is due to a
corrosive atmosphere. (Refer to the limited warranty for complete terms and conditions).
PRODUCTS TO AVOID
AREAS LIKELY TO HAVE CONTAMINANTS
Spray cans containing fluorocarbons
Dry cleaning/laundry areas and establishments
Permanent wave solutions
Swimming pools
Chlorinated waxes/cleaners
Metal fabrication plants
Chlorine-based swimming pool chemicals
Beauty shops
Calcium chloride used for thawing
Refrigeration repair shops
Sodium chloride used for water softening
Photo processing plants
Refrigerant leaks
Auto body shops
Paint or varnish removers
Plastic manufacturing plants
Hydrochloric or Muriatic acid
Furniture refinishing areas and establishments
Cements and glues
New building construction
Antistatic fabric softeners used in clothes dryers
Remodeling areas
Chlorine-type bleaches, laundry detergents, and cleaning solvents
Garages and workshops
Adhesives used to fasten building products
Table 1 –Chemical Contaminants
D. INSULATION BLANKETS
For installation of insulation blankets, refer to Solar Water Heating System Design and Installation Guidelines, SRCC OG-300.
E. DOMESTIC HOT WATER SCALD PREVENTION
F. FREEZE PROTECTION
NOTE: Consider piping and installation when determining drain back tank location. Place tank in location not prone to freezing.
APPROXIMATE TIME / TEMPERATURE RELATIONSHIPS IN SCALDS
120oF
More than 5 minutes
125oF
1 ½ to 2 minutes
130oF
About 30 seconds
135oF
About 10 seconds
140oF
Less than 5 seconds
145oF
Less than 3 seconds
150oF
About 1 ½ seconds
155oF
About 1 second
Table 2
Households with small children, disabled, or elderly persons may require a 120oF
or lower temperature setting to prevent severe personal injury or death due to
scalding.

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LP- 351b REV. 2.3.14
Failure of the solar system due to freeze related damage IS NOT covered by warranty.
In order to meet health and safety regulations, solar system antifreeze fluid should be food grade polypropylene glycol, FDA rated as
“generally recognized as safe” (GRAS). The recommended glycol is DOWFROST or equivalent. Using proper concentrations of glycol,
solar systems can be operated at ambient temperatures as low as -60oF. Freeze tolerance limits are based upon an assumed set of
environmental conditions. Refer to the specification sheet included with the glycol for recommended concentrations. A glycol/water mix
must not exceed 50%, unless the manufacture specifies that a different ratio is recommended for use with solar water heaters. Glycol
may need to be changed periodically (every 3-5 years) to prevent it from becoming acidic; please refer to the guidelines provided by the
glycol manufacturer regarding replacement.
PART 2 - GENERAL INFORMATION
A. PIPING
Collector piping requires the use of copper and brass fittings in the collector loop. To avoid leaks and fluid loss, copper and brass
ground joint unions should be used to join the collectors. Use only lead-free solder. Engelhard Silvabrite 100 or equivalent is the
required soldering material. Use of 50/50 lead solder is expressly prohibited. Use of galvanized steel, CPVC, PVC or any other non-
rated plastic pipe is prohibited.
Piping in new solar installations may have dirt, grease, solder flux, or other impurities that will affect the quality of glycol heat transfer
fluid over time. Thorough cleaning is required before charging new solar installations with glycol.
All vertical piping between the drain back tank and collector(s) shall be supported at each story or at maximum intervals of ten feet (10').
In addition, all non-vertical solar collector piping should pitch ¼” per foot down to the drain back tank to facilitate proper drainage.
Ensure that there are no dips or low points in solar piping that could trap fluid and possibly rupture in freezing conditions. Copper
plumbers tape or tube strap is the required strapping material. The pipe insulation may not be compressed or crimped by the strapping
material.
The installation of all piping may not reduce the performance or rating of structural members or fire rated assemblies and must adhere
to all applicable local codes and ordinances.
B. SIZING THE DRAIN BACK TANK
To ensure proper operation of the drain back solar system, the drain back tank volume should be sized with double the volume capacity
of the total volume of the solar collectors and all solar piping above the drain back tank.
For example:
An HP-30SC Evacuated tube solar collector has a .3 gallon capacity.
100 feet of 1” copper pipe has a 4.6 gallon capacity.
The capacity of the collector and piping equals 4.9 gallons.
The system requires a 10 gallon drain back tank.

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LP- 351b REV. 2.3.14
PART 3 - SPECIFICATIONS
Figure 1 –Drain Back Tank Specifications and Dimensions

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LP- 351b REV. 2.3.14
Figure 2 –Drain Back Tank Specifications and Dimensions

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LP- 351b REV. 2.3.14
PART 4 - INSTALLATION
A. DRAIN BACK TANK LOCATION
To minimize expense and heat loss, locate the drain back tank as centrally to the solar tank and near the solar collectors as possible.
The tank must also be located in as warm a location as possible, away from areas which would subject the drain back reservoir to
freezing temperatures. The drain back tank has no controls, but the sight glass must have clearance for inspection and service.
In addition, the solar water heater should be installed with plenty of clearance for service. If minimum clearances are not met, it may not
be possible to service the heater without removing it from its location.
The drain back tank should also be installed in a place where T&P discharge or a leak will not result in damage to the surrounding area.
Install a 2” high catch pan with a minimum of ¾” drain line to prevent water damage if leakage should occur (See Figure 3).
Figure 3 –Catch Pan Illustration
Filled hot water storage and drain back tanks are very heavy, and should be located in areas that can structurally support such weight.
Failure to properly locate water storage tanks could result in property damage, personal injury, or death.
B. SYSTEM PIPING AND PLUMBING
NOTE: To ensure proper drainage, consider system piping BEFORE making a final decision on collector mounting.
It is very important that you do the potable piping before you pipe into your solar system. Failure to do so may damage your water
heater.
Do not introduce heat transfer fluids into any fittings on the heater except those clearly marked for that purpose.
It is mandatory that plumbing be done in accordance with all local and state plumbing codes. FAILURE TO DO SO WILL VOID THE
WARRANTY.
All solar collectors must be installed level. All non-vertical supply and return solar piping must be pitched at a minimum of ¼” per foot for
drainage and must drain without any fluid traps to prevent freezing. Ensure there are no dips, low points, or piping configurations that
may trap fluid and rupture in freezing conditions.
ALL PIPING AND PLUMBING CONNECTIONS SHOULD BE MADE WITH COPPER PIPE ONLY. No less than ¾” I.D. copper tube of
the type meeting local codes must be used for piping. Pipe runs must be solidly attached with proper clamping methods. Soldered
connections should be secured with 95/5 lead-free solder. No check valves are allowed within the solar piping loop. Remove integral
check from pump if so equipped.
Insulate pipe with ¾” pipe insulation rated for 250oF minimum. Insulate all hot water piping and all exposed cold water piping at the
entrance to the solar tank. Paint pipe insulation exposed to ultraviolet radiation with insulation manufacturer approved UV resistant latex
based paint, or wrap with PVC pipe wrap. Support piping with plumbers straps or pipe hangers and install in such a manner as to not
crush the insulation.
C. INSTALLATION OF THE DRAIN BACK TANK
Never use dielectric unions or galvanized steel fittings on any domestic water connections or auxiliary connections. ONLY use copper
or brass fittings. Teflon thread sealant must be used on all connections.

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LP- 351b REV. 2.3.14
1. DRAIN BACK TANKS WITHOUT HEAT EXCHANGERS
a. Pipe solar collector return to the inlet fitting located on the top of the drain back tank.
b. Pipe drain back tank outlet (located near the bottom of the tank) to the solar heat exchanger inlet.
c. Pipe solar heat exchanger outlet to the solar collector supply fitting.
(See installation diagrams in Part 5 for piping details.)
2. DRAIN BACK TANKS WITH HEAT EXCHANGERS
a. Pipe solar collector return to the inlet fitting located on the top of the drain back tank.
b. Pipe drain back tank outlet to the solar collector supply fitting.
c. Pipe cold supply water from the solar storage tank to the heat exchanger inlet fitting located on the drain back tank.
d. Pipe heat exchanger outlet to hot return fitting on solar storage tank.
(See installation diagrams in Part 5 for piping details.)
Insulate all hot water lines, as well as the final 5’ of cold water supply pipe leading to the system, with at least ¾” thick heat resistant
rubber tubing insulation.
Before commissioning the system, install the sight glass and an ASME/ANSI rated 30 PSI pressure relief valve into the appropriate
fittings on the drain back tank using pipe dope. Follow further pressure relief valve installation information listed below.
To avoid water damage or scalding due to relief valve operation:
Discharge line must be connected to relief valve outlet and run to a safe place of disposal. Terminate the discharge line in a
manner that will prevent possibility of severe burns or property damage should the relief valve discharge.
Discharge line must be as short as possible and the same size as the valve discharge connection throughout its entire length.
Discharge line must pitch downward from the valve and terminate at least 6” above the floor drain, making discharge clearly
visible.
The discharge line shall terminate plain, not threaded, with a material serviceable for temperatures of 375oF or greater.
Do not pipe discharge to any location where freezing could occur.
No valve may be installed between the relief valve and heater or in the discharge line. Do not plug or place any obstruction in
the discharge line.
Test the operation of the relief valve after filling and pressurizing the system by lifting the lever. Make sure the valve
discharges freely. If the valve fails to operate correctly, immediately replace with a new, properly rated relief valve.
Test relief valve at least once annually to ensure the waterway is clear. If valve does not operate, turn the heater “off” and call
a plumber immediately.
Take care whenever operating relief valve to avoid scalding injury or property damage.
FAILURE TO COMPLY WITH THE ABOVE GUIDELINES COULD RESULT IN FAILURE OF RELIEF VALVE OPERATION,
RESULTING IN POSSIBILITY OF SUBSTANTIAL PROPERTY DAMAGE, SEVERE PERSONAL INJURY, OR DEATH.
The circulating pump becomes very hot when running. Allow sufficient time to cool before touching. Failure to do so can lead to
personal injury.
D. SOLAR SYSTEM PUMP
Solar pumps must be installed at least 3’ below drain back tank level. Remove integral check if so equipped. The solar system pump
must be sized to lift water to the top of the collector array. The solar pump must be sized for proper flow and head loss. Friction losses
must also be considered when sizing a pump and solar system piping.
When sizing the pump, determine the head losses (also called psi, head feet, and foot lift). Determine head loss through piping and the
heat exchanger using the solar collector manufacturer’s recommended flow rates. Consider the vertical lift from the drain back tank to
the top of the solar panels. Size the pump for whichever is greater: Head loss pumping through the system, or vertical lift, not both. A
solar modulating pump control is highly recommended on a drain back system.
If the pump continues pumping at full speed rate after the system is primed, the solar loop will often be over-pumped and the
recommended velocity will be exceeded. This condition will lead to premature failure and reduced performance of the solar system.
E. ELECTRICAL INSTALLATION
ALL CONNECTIONS MUST BE MADE IN ACCORDANCE WITH LOCAL ELECTRICAL CODES. A qualified electrician or contractor is
required to install a 115-120VAC duplex receptacle adjacent to the solar storage tank. This receptacle is used to supply power to the
pump/control combo.

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LP- 351b REV. 2.3.14
F. DRAIN BACK TANK WITH BACK UP GAS WATER HEATER DETAIL
Figure 4 –Drain Back System with Gas Back Up
FIGURE NOTES:
1. This drawing is meant to demonstrate system piping concept only. The installer is responsible for all equipment and detailing by local
codes.
2. Non-potable HTF shall only be used for the solar heat exchanger circuit. Never introduce non-potable HTF to any connection other
than the solar loop.
3. If there is a check valve on the cold water feed line, a thermal expansion tank suitable for potable water must be sized and installed
within this piping system between the check valve and cold water inlet of the solar water heater. The expansion tank should be properly
sized for the volume of stored hot water and maximum tank temperature. Normal solar control settings may be between 120oand 160o.
Do not exceed 160oon the solar control setting.
4. A solar rated mixing valve is recommended if the domestic hot water setting is above 120oF. A standard mixing valve generally
cannot deliver the temperature protection range at which a solar system operates.
5. A minimum of 12 diameters of straight pipe must be installed upstream of all circulators.
6. Make sure solar storage tank is fully purged of air before power is turned on to the backup heat source.
7. Due to extreme temperatures, circulators with integral flow checks are not to be used in solar systems. If circulator comes
equipped with an integral flow check, remove it.
8. Non-vertical drain back solar system piping should pitch ¼” per foot back to the tank to facilitate draining.
9. No check valves are allowed in the solar loop.
10. Solar pumps must be installed 3’ below the drain back tank.

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LP- 351b REV. 2.3.14
G. DRAIN BACK TANK WITH BOILER AND INDIRECT WATER HEATER DETAIL
Figure 5 –Drain Back System with Boiler Back Up
FIGURE NOTES:
1. This drawing is meant to demonstrate system piping concept only. The installer is responsible for all equipment and detailing by local codes.
2. Non-potable HTF shall only be used for the solar heat exchanger circuit. Never introduce non-potable HTF to any connection other than the solar
loop.
3. If there is a check valve on the cold water feed line, a thermal expansion tank suitable for potable water must be sized and installed within this piping
system between the check valve and cold water inlet of the solar water heater. The expansion tank should be properly sized for the volume of stored hot
water and maximum tank temperature. Normal solar control settings may be between 120oand 160o. Do not exceed 160oon the solar control setting.
4. A solar rated mixing valve is recommended if the domestic hot water setting is above 120oF. A standard mixing valve generally cannot deliver the
temperature protection range at which a solar system operates.
5. A minimum of 12 diameters of straight pipe must be installed upstream of all circulators.
6. Make sure solar storage tank is fully purged of air before power is turned on to the backup heat source.
7. Circulators shown in the above hydronic piping should have an integral flow check or alternately use a stock pump with an external spring type check
valve. (Due to extreme temperatures, circulators with integral flow checks are not to be used in solar systems. If circulator comes equipped
with an integral flow check, remove it.)
8. Non-vertical drain back solar system piping should pitch ¼” per foot back to the tank to facilitate draining.
9. No check valves are allowed in the solar loop.
10. Solar pumps must be installed 3’ below the drain back tank.

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H. DRAIN BACK TANK WITH HEAT EXCHANGER
Figure 6 –Drain Back System with Heat Exchanger
FIGURE NOTES:
1. This drawing is meant to demonstrate system piping concept only. The installer is responsible for all equipment and detailing by local
codes.
2. Non-potable HTF shall only be used for the solar heat exchanger circuit. Never introduce non-potable HTF to any connection other
than the solar loop.
3. If there is a check valve on the cold water feed line, a thermal expansion tank suitable for potable water must be sized and installed
within this piping system between the check valve and cold water inlet of the solar water heater. The expansion tank should be properly
sized for the volume of stored hot water and maximum tank temperature. Normal solar control settings may be between 120oand 160o.
Do not exceed 160oon the solar control setting.
4. A solar rated mixing valve is recommended if the domestic hot water setting is above 120oF. A standard mixing valve generally
cannot deliver the temperature protection range at which a solar system operates.
5. A minimum of 12 diameters of straight pipe must be installed upstream of all circulators.
6. Make sure solar storage tank is fully purged of air before power is turned on to the backup heat source.
7. Due to extreme temperatures, circulators with integral flow checks are not to be used in solar systems. If circulator comes
equipped with an integral flow check, remove it.
8. Non-vertical drain back solar system piping should pitch ¼” per foot back to the tank to facilitate draining.
9. No check valves are allowed in the solar loop.
10. Solar pumps must be installed 3’ below the drain back tank.
11. The drain back tank must be properly supported to account for the weight of the tank when filled with HTF.

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PART 5 - FLUID QUALITY
Two heat transfer fluids may be used in drain back systems: Distilled water or glycol/water mix.
In order to meet health and safety regulations, drain back system antifreeze fluid should be food grade polypropylene glycol, FDA rated
as “generally recognized as safe” (GRAS). Using proper concentrations of glycol, solar systems can be operated at ambient
temperatures as low as -60oF. Freeze tolerance limits are based upon an assumed set of environmental conditions. Refer to the glycol
manufacturer’s specification sheet for recommended concentrations.
If using a glycol/water mix, the water must meet the above requirements, and the glycol content of the liquid must not exceed 50%,
unless the manufacture specifies that a different ratio is recommended for use with solar water heaters. HTP recommends using a pre-
blended solution. Glycol/water mix should be tested for pH and freeze protection annually, and may need to be changed periodically
(every 3-5 years) to prevent it from becoming acidic. Please refer to the guidelines provided by the glycol manufacturer regarding
replacement and balancing additives.
NOTE: HTP DOES NOT WARRANT THE DRAIN BACK TANK AGAINST FREEZE RELATED DAMAGE.
PART 6 –INSTALLING THE SOLAR DRAIN BACK TANK SIGHT GLASS
IMPORTANT NOTE: A sight glass has been included with the solar drain back tank. The sight glass allows service technicians,
installers, and users to quickly determine proper drain back system drainage and solar system heat transfer fluid level.
It is extremely important that this sight glass be installed BEFORE filling the solar water heating system. Failure to install the sight glass
will result in a spillage of heat transfer fluid, which, depending on your system, may or may not contain antifreeze. Property damages
due to failure to install the sight glass ARE NOT covered by product warranty.
1. Remove the two brass fittings, washers, and rubber gaskets from the brass sight glass fittings installed on the solar drain back tank.
2. Place a brass fitting (threaded end facing out), washer, and rubber gasket on each end of the sight glass. See Figure 7.
Figure 7 –Installing the Brass Fitting, Washer, and Gasket Figure 8 –Sight Glass Connected to Brass Fitting
2. Use pipe dope and a pipe wrench to connect each end of the sight glass to the brass fittings
provided on the drain back tank. See Figure 8.
3. Using the sight glass as a guide, use a drill with a Phillips Head bit to install the snap fittings
into the tank with the included 6 X 1 screws. The snap fittings should be spaced roughly one
foot from each fitting, and the sight glass should run as straight as possible when installed into
the snap fittings.
4. Snap the sight glass into the snap fittings. See Figure 9. Sight glass installation is complete.
5. After solar water heating installation is complete, fill the system and check the sight glass for
any leaks. Repair as necessary.
Figure 9 –Installed Sight Glass with Snap Fittings

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PART 7 - STARTING YOUR DRAIN BACK SYSTEM
NOTE: DO NOT MOVE ON TO THESE STEPS UNTIL THE ENTIRE SOLAR SYSTEM, INCLUDING ALL PIPING, SOLAR
COLLECTORS, SENSORS, PUMPS, CONTROLS, AND ELECTRICAL CONNECTIONS, ARE PROPERLY SECURED, INSULATED,
LABELED, AND INSTALLED.
A. FILL THE DRAIN BACK RESERVOIR
1. Attach hose to solar loop fill valve. The location of the fill valve varies depending on numerous factors, including whether the
drain back tank has a heat exchanger.
2. Open fill valve and the bleed valve on the drain back tank sight glass (see Specification diagram for location, Figure 1).
3. Slowly fill the drain back reservoir to the top of the sight glass.
4. When nearly full, close bleed valve, and add between 2 and 5 PSI head pressure to the system. When system is full and at
desired head pressure, shut off fill valve.
5. Remove fill hose.
Take care not to overfill the drain back solar system. Overfilling will cause a potentially dangerous condition that could lead to freezing
and failure of the solar system.
B. START-UP PROCEDURE
Once the system is filled as prescribed above:
1. Apply power to the solar controller.
2. Set controller to operate pump manually. Let pump run for 5 minutes.
3. Check for leaks at collectors and in attic, if applicable.
4. If no leaks are found, program controller for your drain back system (see solar controller programming instructions).
If the sun is shining and the tank is cool, the pump should turn on and begin circulating water. Check control settings to maximize your
system performance.
PART 8 - SERVICE/MAINTENANCE PROCEDURES
A. SHUT DOWN PROCEDURE
To shut down the drain back system, simply unplug the differential controller. The pump will stop and water will drain out of the
collectors into the reservoir.
Never open the pressure relief valve while the system is in operation or hot water is present. Allow to cool prior to opening.
B. DRAINING THE DRAIN BACK RESERVOIR
1. Unplug the controller and wait until all water returns to the reservoir.
2. Attach hose to fill valve.
3. Open the pressure relief valve (see the caution statement above).
4. Open fill valve.
5. Allow the system to completely drain.
6. Close fill valve and the pressure relief valve.
7. Remove drain hose.
C. ROUTINE MAINTENANCE
The heat transfer fluid level in the drain back reservoir should be checked twice a year. With the system turned off, make sure that the
water level in the reservoir reaches the top of the sight glass. If not, follow the instructions in Part 6, Section A: “FILL THE DRAIN BACK
RESERVOIR”.
Periodically check the temperature difference between the collector supply (from the tank to the collector) and collector return lines
(from the collector to the tank). As a rule, an 8 –12° temperature gain should be expected across a collector, in bright sun, at the proper
flow rate. Larger systems may have a greater temperature difference.
D. VACATION PROCEDURES
If hot water is not to be used for an extended period of time, unplug the controller and allow the solar collectors and piping to drain into
the drain back reservoir. To re-energize, simply plug in the controller.

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LP- 351b REV. 2.3.14
PART 9 - TROUBLESHOOTING
Owners are advised to contact the installer whenever in-depth interaction with the solar system is required.
A. LEAKS
For leaks in the solar system piping, shut down the system by pulling the plug on the solar controller and call a plumber.
B. OTHER PROBLEMS
A noisy pump could be an indication of worn bearings, obstruction, or a leak in your system. Call your installer for diagnosis of the
problem, repair of the system, and/or replacement of components.
For your safety, DO NOT attempt repair of electrical wiring, thermostat, heating element or other operating controls. Refer repairs to
qualified service personnel.
INSTALLATION AND MAINTENANCE NOTES

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LP- 351b REV. 2.3.14
HTP CUSTOMER INSTALLATION RECORD FORM
The following form should be completed by the installer for you to keep as a record of the installation in case of a warranty claim. After
reading the important notes at the bottom of the page, please also sign this document.
Customer’s Name:
Installation Address:
Date of Installation:
Installer’s Code/Name:
Product Serial Number(s):
Comments:
Installer’s Phone Number:
Signed by Installer:
Signed by Customer:
IMPORTANT NOTES:
Customer: Please only sign after the installer has reviewed the installation, safety, proper operation and maintenance of the
system. In the case that the system has any problems, please call the installer. If you are unable to make contact, please
contact your HTP Sales Representative.
Distributor/Dealer: Please insert contact details.