Crown Boiler Mega-Stor MS-26 User manual

DESIGNED TO LEAD
Manufacturer of Hydronic Heating Products
P.O. Box 14818 3633 I. Street
Philadelphia, PA 19134
www.crownboiler.com
Mega-Stor
TM
Stainless Steel, Indirect Water Heaters
• INSTALLATION AND OPERATING INSTRUCTIONS
• ENGINEERING MANUAL
• MAINTENANCE
• PARTS
CAUTION
1. The heat transfer-medium must be water or other nontoxic uid
having a toxicity rating or Class of 1, as listed in Clinical Toxicol-
ogy of Commercial Products, 5th edition.
2. The pressure of the heat transfer medium must be limited to a
maximum of 30 PSIG by an approved safety or relief valve.

1
CONTENTS
I. Product Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
II. Specications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
III. Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
IV. Zone Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
V. Before Starting Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
VI. Locating The Mega-Stor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
VII. Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Boiler Side Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Domestic Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
VIII. Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
IX. Start-up and Check-out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
X. Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
XI. Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2
I. PRODUCT DESCRIPTION
The Crown Mega-Stor series indirect water heater is designed to generate domestic hot water in conjunction with a hot water
boiler using forced boiler water circulation. This indirect water heater consists of a stainless steel tank in which a smooth stainless
steel coil is located. Boiler water is pumped through the coil and heats the water in the tank. This tank is not intended for use in
pool heating applications or for heating any other uid other than water. It is also not intended for use in gravity hot water heating
systems.
IMPORTANT NOTE
Some localities require indirect water heaters having a relief valve capacity in excess of 200,000 BTU/hr to be con-
structed and stamped in accordance with ASME requirements. Check with the local authority having jurisdiction before
installing an MS-79 or MS-119 with a boiler or boilers having a total gross output in excess of 200,000 BTU/hr.
II. SPECIFICATIONS
TABLE 2.1: AHRI PERFORMANCE SPECIFICATIONS
Notes:
AHRI ratings based on 77F DHW temperature rise (135F outlet temp) and 180F boiler supply temperature. The ratings in
Table 2.1 were obtained at the heat source (boiler) output rates and heat source ow rates shown above. Other results shall
be obtained under different conditions.
Pressure Ratings:
Maximum Allowable Tank Working Pressure - 150 psi
Design Hydrostatically Tested to 300 psi
Model
First Hour
Rating
Continuous
Draw Rating Standby
Loss
(°F/hr)
Minimum
Boiler
Output
(MBH)
Boiler Water Through Coil
(Gal/hr) (Gal/hr) Min Flow
(Gal/min)
Head Loss
(ft w.c.)
MS-26 144 121 1.7 77 8.0 2.5
MS-40 195 157 1.4 102 8.0 3.0
MS-53 226 179 0.9 114 8.0 3.5
MS-79 287 218 1.0 145 8.0 4.8
MS-119 472 384 1.4 225 12.7 7.9
MSH-40 151 116 1.4 75 8.0 2.5
MSH-53 203 158 1.3 101 8.0 3.5

3
Model
Potable
Volume
(Gal.)
Dimensions in Inches Coil
Surface
(Sq. Ft.)
Weight
A B C D E F G H Net Full
MS-26 25.6 38-3/4 20-1/4 2 9-3/4 22-1/2 --- --- --- 6.5 57 269
MS-40 38.7 54-3/4 20-1/4 2 9-3/4 25-3/4 --- --- --- 8.6 77 396
MS-53 51.1 47-7/8 23-7/8 2 9-7/8 26-3/4 --- --- --- 10.1 103 522
MS-79 80.0 69-1/4 23-3/4 1-5/8 10-1/4 29-1/4 59-1/4 --- --- 15.1 204 831
MS-119 111.7 66 29-1/2 2-1/2 12-3/4 36-1/4 52-3/4 --- --- 24.3 218 1178
MSH-40* 37.6 24-3/8 23-7/8 34-11/16 3-5/8 5 10-1/8 16-7/8 19-3/8 6.7 127 449
MSH-53* 51.0 24-3/8 23-7/8 44-7/8 3-5/8 5 10-1/8 16-7/8 19-3/8 9.8 168 595
FIGURE 2.2: MEGA-STOR INDIRECT WATER HEATER
*Horizontal Tank
Key # Description
Size (NPT)
MS-26
MS-53
MSH-40
MSH-53 MS-79 MS-119
1Cold Water Inlet 3/4M 3/4M 1M 1-1/4M
2 To Boiler Return 3/4M 3/4M 3/4M 1-1/4M
3 From Boiler Supply 3/4M 3/4M 3/4M 1-1/4M
4T&P Valve Tapping --- 3/4F 1F 1F
5Hot Water Out 3/4M 3/4M 1F 1-1/4F
1
2
3
5
4
REAR
RH SIDEFRONT
"H"
"G"
"F"
"E"
"D"
"A"
"B"
HAND HOLE
(UNDER COVER)
CONTROL
"C"
SHOWN WITH OPTIONAL
MOUNTING KIT FOR
MS-40H AND MS-53H
Horizontal Tank
Horizontal Tank
CONTROL
COLD WATER INLET/
DRAIN CONNECTION
AF
B
5
5
E
DC
HOT WATER OUT
AND T&P VALVE
(MS-26 Ð MS-53)
INSULATED HANDHOLE
JACKET COVER
T&P VALVE TAPPING
(MS-79, MS-119)
FROM BOILER SUPPLY
TO BOILER RETURN
HOT WATER OUT
(MS-79, MS-119)
4
3
2
1
Vertical Tank
Vertical Tank
TABLE 2.3: PHYSICAL SPECIFICATIONS
TABLE 2.4: CONNECTIONS

4
IMPORTANT
The following procedures are used to size indirect water heaters based on the amount of hot water which will be required
during a given hour. In doing so it is assumed that this demand will be evenly spread out over the course of the entire
hour.
THESE SIZING PROCEDURES ARE PROVIDED AS A GUIDE TO ASSIST THE PROFESSIONAL CONTRACTOR
IN SIZING MEGA-STOR TANKS. BECAUSE OF THE LARGE VARIETY OF DEMAND SITUATIONS
ENCOUNTERED IN THE FIELD, CROWN BOILER COMPANY CANNOT GUARANTEE THE SUITABILITY OF
THESE PROCEDURES TO ALL INSTALLATIONS.
Residential Applications
Table 3.1 shows the minimum sized Mega-Stor that should be considered for one and two family homes based on the numbers
of bedrooms and bathrooms being served. In cases where the boiler is sized signicantly larger than that shown in column (d) in
order to meet space heating demand, there is usually no need to add boiler capacity just for the Mega-Stor. Note that the sizing
recommendations shown in Table 3.1 may not provide satisfactory performance when there are unusually high peak demands,
such as when multiple showers are used simultaneously or when a Whirlpool tub is lled. To address these cases, review Tables
3.2 and 3.3 and make adjustments to Mega-Stor and/or boiler size, to make sure that the peak demand can be satised. For Whirl-
pool tubs, it is recommended that the Mega-Stor have a domestic water volume at least as large as the nominal volume of the tub.
Commercial Applications
Use a xture count method to determine the domestic hot water demand, such as that shown in the Service Water Heating chap-
ter of the ASHRAE Applications Handbook. Then use the data provided in Tables 2.1, 3.2, and 3.3 to select the boiler and Mega-
Stor.
Table 3.1: Mega-Stor Sizing for Typical One and Two Family Units
(a) (b) (c) (d) (e)
Number of
Bathrooms
Number
of Bed-
rooms
Mega-Stor
First Hour
Requirement
(GPH)
Min. Boiler Output
(MBH)
1 to 1 1/2
1 MS-26 43 27
2 MS-40 60 36
3 MS-40 60 36
2 to 2 1/2
2 MS-40 60 36
3 MS-40 70 36
4 MS-40 72 38
5 MS-53 90 47
3 to 3 1/2
3 MS-53 72 47
4 MS-53 82 47
5 MS-53 90 47
6 MS-53 92 47
III. SIZING

5
Table 3.2: Maximum Possible Continuous Draw
(180F Boiler Supply, 77F DHW Rise, 135F Outlet)
(a) (b) (c)
Mega-Stor Continuous Draw
(Gal/min)
Min Boiler Output
(MBH)
MS-26 2.0 77
MS-40 2.6 102
MS-53 3.0 114
MS-79 3.6 145
MS-119 6.4 225
MSH-40 1.9 75
MSH-53 2.6 101
Table 3.3: AHRI First Draw Rating*
(a) (b) (c)
Mega-Stor Draw Rate
(GPM)
First Draw Rating
(Gal)
MS-26 2.0 22.6
MS-40 2.6 38.2
MS-53 3.0 46.5
MS-79 3.6 69.3
MS-119 6.4 88.3
MSH-40 1.9 35.6
MSH-53 2.6 44.6
* First Draw Rating is the amount of stored water available from a fully recovered Mega-Stor, with no boiler output during the
draw, before the outlet temperature falls by 25F. At draw rates higher than that shown in column (b), less stored hot water may be
available.

6
IV. ZONE DESIGN
IMPORTANT
All First Hour Ratings shown in this manual are based on the boiler water ow rates shown in Table 2.1. Read this
section for information on sizing, piping and circulators for the Mega-Stor zone.
In designing the Mega-Stor zone piping system the following points should be considered:
1) Circulator or Zone Valve Zoning? - Circulator zones are usually a better choice. Zone valves have a relatively high
pressure drop at the ow rate required through the Mega-Stor coil (see Table 2.1). If zone valves are selected, use a zone
valve with a minimal delay in opening, such as a motorized type.
2) Priority Zoning - Priority zoning is used to divert all boiler output to the Mega-Stor when its zone calls for heat re-
gardless of any simultaneous calls for heat from space heating zones. Priority zoning can be done using a 3-way zone
valve, or by using a relay to de-energize the heating zones when the Mega-Stor calls for heat. See the Piping and Wiring
Sections for more information on these zone systems.
3) Use Worksheet 1 to size piping and select a circulator for the Mega-Stor zone. To do this:
a) Use column (a) to enter the total number of each type of tting. For straight pipe enter the total number of
feet. When counting ttings, count all ttings in the Mega-stor zone as well as all ttings in the piping common
to all zones (zone manifolds, etc.).
b) Refer to Table 1 to nd the required ow rate through the Mega-Stor coil.
c) Columns (b) and (c) each show pressure drops for ttings at a given ow rate. Select the appropriate column
for the required ow rate. Multiply the number of each type of tting by the pressure drop in the column
selected. Enter the result in column (d).
d) Total column (d). This is the total pressure drop for the Mega-Stor zone.
e) Use Table 4.1 or a circulator manufacturer’s literature to select a circulator which will develop the required
ow rate at the pressure drop calculated.
TABLE 4.1: SELECTING A CIRCULATOR
AVAILABLE HEAD (FT. W.C.)
Select a circulator which has an Available Head greater than the pressure drop calculated using Worksheet 3.
Circulator Flow
8.0 GPM 12.7 GPM
Taco 007 8.2 5.8
Taco 008 9.8 4.2
Taco 0014 17.5 15.2
Grundfos UPS 15-42F 9.0 5.0
Grundfos UP 26-64F 21.0 16.0

7
Fitting Description Quantity
(a)
Flow
Total
(d)
8.0 GPM
(b)
12.7 GPM
(c)
MS-26, MSH-40 Coil 2.5 ---
MS-40 Coil 3.0 ---
MS-53, MSH-53 Coil 3.5 ---
MS-79 Coil 4.8 ---
MS-119 Coil --- 7.9
1 ft 1” St. Pipe ft 0.05 0.13
1 ft 1-1/4” St. Pipe ft 0.01 0.03
1 ft 1-1/2” St. Pipe ft 0.01 0.01
1” 90 El 0.16 0.40
1-1/4” El 0.06 0.15
1-1/2” El 0.04 0.10
1” Run of Tee 0.05 0.13
1-1/4” Run of Tee 0.02 0.05
1-1/2” Run of Tee 0.01 0.03
1” Branch of Tee 0.26 0.66
1-1/4” Branch of Tee 0.08 0.20
1-1/2” Branch of Tee 0.05 0.13
1” Std. Ball Valve 0.12 0.30
1-1/4” Std. Ball Valve 0.06 0.15
1-1/2” Std. Ball Valve 0.02 0.05
Taco
“Flo-Chek”
#220 (1”) 2.18 5.49
#221 (1-1/4”) 0.84 2.12
#222 (1-1/2”) 0.44 1.11
Taco Air
Scoop
#431 (1”) 0.15 0.38
#432 (1-1/4”) 0.05 0.25
Honeywell Zone Valves
V8043F1101 (1” Cv=8) 2.31 4.69
Allowance for bushings and
sudden transitions*
1 0.53 1.34
Boiler**
Total Head Loss Through Manifold Piping and Mega-Stor Zone
WORKSHEET 1:
PRESSURE DROP CALCULATIONS THROUGH MEGA-STOR ZONE
HEAD LOSS (FT W.C.)
*Includes (2) 1-1/2 x 3/4 and (2) 1-1/2 x 1 transitions
**Pressure drop through boiler can be ignored for most cast iron or steel boilers. If in doubt, consult the boiler
manufacturer.
Above pressure drops may be used for black pipe or copper tubing.

8
EXAMPLE 1
Size a circulator for the Mega-Stor zone shown below. An MS-40 is to be used with an 8 GPM ow rate through the coil.
1) Using Worksheet 1, record the total number of ttings in Mega-Stor zone and piping common to all zones (piping
shown in bold) in column (a).
2) Since 8 GPM is required, use the pressure drops shown in column (b). Multiply each entry in column (a) by the corre-
sponding pressure drop in column (b). Enter the result in column (d).
3) The total of column (d) is 7.94 ft. of head. This is the total pressure drop for the Mega-Stor zone.
4) Select a pump which will develop 7.94 ft of Head at 8 GPM. From Table 4.1, we see that either a Taco 007 or a Grund
fos UPS 15-42F can be used.
EXAMPLE 1: SIZING A CIRCULATOR AND PIPING FOR THE MEGA-STOR ZONE

9
Fitting Description Quantity
(a)
Flow
Total
(d)
8.0 GPM
(b)
12.7 GPM
(c)
MS-26 Coil, MSH-40 Coil 2.5 ---
MS-40 Coil 3.0 --- 3.0
MS-53, MSH-53H Coil 3.5 ---
MS-79 Coil 4.8 ---
MS-119 Coil --- 7.9
1 ft 1” St. Pipe 10 ft 0.05 0.13 0.50
1 ft 1-1/4” St. Pipe 6 ft 0.06 0.03 0.36
1 ft 1-1/2” St. Pipe ft 0.01 0.01
1” 90 El 6 0.16 0.40 0.96
1-1/4” El 3 0.06 0.15 0.18
1-1/2” El 0.04 0.10
1” Run of Tee 0.05 0.13
1-1/4” Run of Tee 1 0.02 0.05 0.02
1-1/2” Run of Tee 0.01 0.03
1” Branch of Tee 0.26 0.66
1-1/4” Branch of Tee 2 0.08 0.20 0.16
1-1/2” Branch of Tee 0.05 0.13
1” Std. Ball Valve 0.12 0.30
1-1/4” Std. Ball Valve 0.06 0.15
1-1/2” Std. Ball Valve 0.02 0.05
Taco
“Flo-Chek”
#220 (1”) 1 2.18 5.49 2.18
#221 (1-1/4”) 0.84 2.12
#222 (1-1/2”) 0.44 1.11
Taco Air
Scoop
#431 (1”) 0.15 0.38
#432 (1-1/4”) 1 0.05 0.25 0.05
Honeywell Zone Valves
V8043F1101 (1” Cv=8) 2.31 4.69
Allowance for bushings and
sudden transitions*
1 0.53 1.34 0.53
Boiler** 0
Total Head Loss Through Manifold Piping and Mega-Stor Zoning 7.94
FIGURE 4.2: COMPLETED WORKSHEET 3
PRESSURE DROP CALCULATIONS THROUGH MEGA-STOR ZONE
HEAD LOSS (FT W.C.)
*Includes (2) 1-1/2 x 3/4 and (2) 1-1/2 x 1 transitions
**Pressure drop through boiler can be ignored for most cast iron or steel boilers. If in doubt, consult the boiler
manufacturer.
Above pressure drops may be used for black pipe or copper tubing.

10
V. BEFORE STARTING INSTALLATION
Characteristic Min Max
pH 6.0 8.0
Chloride (PPM) 0.0 80.0
TABLE 5.1: WATER CHEMISTRY
REQUIREMENTS
Water used in the Mega-Stor must have characteristics falling
within the following limits:
1) Be sure that the planned installation is in accordance with all local codes.
2) Be certain the domestic water supply to the tank has physical and chemical characteristics that fall within the limits shown
in Table 5.1. Where questions exist as to the composition of the water on the job, a qualied water treatment expert should be
consulted.
3) Read and understand all installation requirements in this manual.
IMPORTANT
Water with characteristics outside the limits shown in
Table 5.1 may severely shorten the life of the tank due to
corrosion. Damage to tanks in such cases is not covered
under warranty.
VI. LOCATING THE MEGA-STOR
1) Table 2.3 shows the weights of all Mega-Stors lled with water. Make sure that the location chosen for the Mega-Stor is
capable of supporting it.
WARNING
Failure to properly support an MS tank could result in property damage or personal injury.
2) Locate the Mega-Stor in a location where a leak in the tank, the adjacent piping, or an open T&P valve will not damage the
surrounding structure. If the area around the desired tank location is highly susceptible to water damage, install the Mega-
Stor in a pan with a drain.
3) The Mega-Stor may be located some distance from the boiler provided the zone system is designed to provide the ow
called for in Table 2.1 through the coil. Also, the further the Mega-Stor is from the boiler, the longer the response of the
boiler will be to a call from the Mega-Stor zone. If long runs exist between the boiler and Mega-Stor it is advisable to
insulate the piping.

11
VII. PIPING
1) BOILER SIDE PIPING
Figures 7.1 thru 7.4 show typical boiler side piping for several common situations. Regardless of which system is used it is impera-
tive that the ow rates called for in Table 1 are developed through the coil. This requires properly sized piping and a properly sized
pump. To determine the pipe/pump sizes required see page 6.
The systems shown in Figures 7.1 thru 7.4 are described below:
STANDARD CIRCULATOR ZONE
This system is just like the circ zone system on a straight heat job except that one of the zones goes to the MS tank instead of radia-
tion. As on any circulator zone system, check valves should be installed in each zone to prevent unwanted circulation through zones
which are not calling for heat. Figure 7.1 illustrates typical circ zone piping.
ZONE VALVE SYSTEM
Figure 7.2 illustrates a typical Mega-Stor installation using zone valves. The circulator must be large enough to move boiler water
through the coil at the ow rate in Table 2.1, regardless of the ow rate required through the heating zones.
3-WAY ZONE VALVE SYSTEM
Figure 7.3 illustrates typical piping using a 3-way zone valve. In this system a 3-way zone valve is used which has a common
port, a “normally open” port, and a “normally closed” port. The zone valve motor is wired so as to be energized by the Mega-Stor
thermostat (see Part VIII for wiring information). The common side of the zone valve is connected to the boiler. The heating zone is
connected to the normally open side of the zone valve and the Mega-Stor coil is connected to the normally closed side of the zone
valve. As long as the Mega-Stor is not calling for heat, boiler water can ow from the space heating zone, through the normally
open side of the 3-way valve, to the boiler. As soon as the Mega-Stor calls for heat, the zone valve is energized, and boiler water
can only ow through the Mega-Stor zone.
MEGA-STOR MANIFOLD PIPING (BOILER SIDE)
Multiple tank installations must be done in the “reverse return” manner illustrated in Figure 7.4. The reason for this is to create the
same pressure drop (and therefore the same ow) through the coil of each tank. The boiler manifold piping must be sized so that
each coil has the ow rate called for in Table 2.1. For example, if two MS-26’s are to be manifolded together, the circulator and
zone piping common to both tanks must be capable of moving 16 GPM (2 x 8GPM).
Because the pressure drop through Mega-Stor coils varies from size to size, it is hard to predict the ow rate that will be developed
through each coil when two Mega-Stors of different sizes are placed in the same manifold. For this reason it is best not to mix
Mega-Stors of two different sizes in the same zone if their recovery is critical.

12
FIGURE 7.1: BOILER-SIDE PIPING USING CIRCULATOR ZONES
FIGURE 7.2: BOILER-SIDE PIPING USING ZONE VALVES (2-WAY)

13
FIGURE 7.4: BOILER-SIDE PIPING FOR MULTIPLE MEGA-STORS
FIGURE 7.3: BOILER-SIDE PIPING USING A THREE WAY ZONE VALVE

14
2) DOMESTIC SIDE PIPING
BASIC DOMESTIC PIPING
Figure 7.6A shows typical domestic water piping for a Mega-Stor. All components except the control are provided by the installer.
The function of the components shown are as follows:
a) Temperature Control (required) - This control is provided by Crown and must be installed in the aquastat
well location of the water heater indicated in Figure 2.2. Remove the cover and loosen the clamping screws. Insert the
capillary bulb so that it is “bottomed out” in the control well as shown in Figure 7.5 and screw the control clamp
securely in the well groove at the end of the well. See Section VIII for wiring details and Section IX for instructions on
adjusting the temperature setting.
b) Shut-off valves (recommended) - Use to isolate the tank for servicing.
c) Backow Preventer (required by some codes) - Use to prevent water from backing out of the Mega-Stor in the event
that inlet water pressure drops.
d) Expansion Tank (required when a backow preventer is used) -This expansion tank absorbs the increased volume
caused by heating water. If a backow preventer is installed, this expansion tank is required because the increased water
volume will otherwise have no place to go and the T&P valve will open. Use an expansion tank designed for use on
domestic water systems such as Watts DET series expansion tank. Refer to the expansion tank manufacturer’s literature
for the proper size expansion tank to use.
IMPORTANT
If an expansion tank is used, do not put any valves between the expansion tank and Mega-Stor inlet.
e) Unions (optional) - Use to disconnect the Mega-Stor in the event that this is necessary.
f) Drain (Required) - Used to drain the tank for inspection or servicing.
g) Temperature/Pressure Relief Valve (required) - Opens to relieve excess pressure or temperature which has developed
in the Mega-Stor. This valve must comply with ANSI Z21.22 Standard for Relief Valves and Automatic gas Shutoff
Devices for Hot Water Supply Systems and must be sized in accordance with Table 7.7.
Pipe this valve as shown in Figure 7.6B or 7.6C. Run the discharge to a location where hot water discharge will not cause
injury or damage. Leave a 6” gap between the T&P valve pipe termination and the drain or closest obstruction. Do not
run T&P valve discharge pipe to the outdoors or other potentially freezing location. Make sure the discharge line is
installed to allow complete drainage of both the valve and line.
h) Vacuum Breaker (Recommended) - This valve protects the tank in the event that the pressure in the tank falls below
atmospheric. Use a Watts N-36 or equivalent.
i) Heat Trap (Optional) - The heat trap retards the migration of heat from the Mega-Stor up the hot water supply pipe.
IMPORTANT
Do not put any valves between the relief valve and the tank.
Do not install a reducing coupling or otherwise restrict the discharge line.

15
25
WARNING
A thermostatic mixing valve does not eliminate the risk of scalding.
* Set the Mega-Stor thermostat as low as practical.
* Feel water before bathing or showering
* If anti-scald or anti-chill protection is required, use devices specically
designed for such service. Install these devices in accordance with their
manufacturer’s instructions.
DOMESTIC WATER PIPING FOR DISTANT FIXTURES
In some cases the furthest xture may be quite distant from the Mega-Stor. In such an installation the conguration shown in
Figure 7.6A or 7.8 would result in an unacceptable delay before hot water reaches these distant xtures. Even if all the xtures are
relatively close to the Mega-Stor, the building owner may want hot water at all xtures as soon as they are opened.
Figure 7.9 illustrates a solution to this problem. In it, a pipe is run from the furthest xture on each branch back to the return of
the Mega-Stor. A small bronze circulator is mounted in this line and is wired so as to run continuously. A check valve in this line
permits ow towards the Mega-Stor inlet only.
MEGA-STOR PIPING WITH A “TEMPERATURE LIMITING VALVE”
Usually, the maximum temperature of the outlet water will stay near the setting of the Mega-Stor control. In some cases, however,
hot water usage patterns can cause the outlet water temperature to rise signicantly above the control setting.
The temperature of water going to the xtures may be more carefully controlled through the use of a thermostatic mixing valve.
This device blends a controlled amount of cold water with the hot water leaving the Mega-Stor so that water at a more constant
temperature exits the mixing valve. Typical thermostatic mixing valve piping is illustrated in Figure 7.8. Consult a licensed
plumber or the local plumbing authority for requirements in your area.
FIGURE 7.5: AQUASTAT INSTALLATION

16
When no xtures are drawing water, the bronze circulator moves hot water from the Mega-Stor to end of the branch just below
the last xture, then back to the inlet of the Mega-Stor via the return pipe. When a xture is opened, hot water is already out in the
branch very close to the xture and hot water appears at it almost immediately. The check valve prevents cold water in the Mega-
Stor’s inlet pipe from passing around the tank and heading directly to the xture.
Because hot water is always circulated in the hot
water branch the entire branch should be insulated to
prevent excessive heat loss.
MANIFOLD DOMESTIC WATER PIP-
ING
Figure 7.10 illustrates the recommended method of
piping the domestic water side of several tanks to-
gether. All Mega-Stors are piped in a “reverse- return”
manner just like the boiler piping. This balances the
pressure drop through each tank, resulting in an even
ow rate through each tank.
Each tank must have its own T&P valve. It is recom-
mended that each tank be equipped with its own isola-
tion valves, unions, and drains so that one tank may
be removed from the system. If local codes require a
backow preventer, check with the appropriate author-
ity to nd out whether one backow preventer may
be used for tanks or each tank must be equipped with
its own backow preventer. If each tank must have its
own backow preventer, each tank must also have its
own expansion tank. If a common backow preventer
is permitted, an expansion tank must be sized to ac-
commodate the expansion volume of all tanks.
TABLE 7.7: MINIMUM T&P VALVE SIZES
*If the Mega-Stor is connected to a boiler which has a Gross Output
LESS than the “Max. T&P Valve Capacity” shown below, install
a T&P valve having a capacity greater than or equal to the boiler’s
Gross Output.
*If the Mega-Stor is connected to a boiler which has a Gross Output
GREATER than the “Max. T&P Valve Capacity” shown below,
install a T&P valve having a capacity greater than or equal to the
“Max T&P Valve Capacity.”
Model Max T&P Valve Capacity (BTU/hr)
MS-26 172,800
MS-40 181,800
MS-53 199,800
MS-79 215,100
MS-119 445,635
MSH-40 103,344
MSH-53 145,289
*Maximum T&P valve pressure setting - 150 psi
FIGURE 7.6A: BASIC DOMESTIC WATER PIPING

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FIGURE 7.6B: CORRECT TEMPERATURE & PRESSURE
VALVE PIPING FOR MS-26, MS-40, MS-53
FIGURE 7.6C: CORRECT TEMPERATURE & PRESSURE VALVE PIPING FOR MS-79, MS-119

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FIGURE 7.8: DOMESTIC HOT WATER PIPING
USING A MIXING VALVE
Check Valves
Bronze or Stainless
Steel Circulator
Keep these tees as
close to fixtures as
practical
Insulate Dashed
Piping
Cold Water In
Crown Mega-Stor
Expansion Tank
Required To Fixtures
FIGURE 7.9: DOMESTIC WATER PIPING FOR DIS-
TANT FIXTURES USING A RECIRCULATION LINE

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FIGURE 7.10: DOMESTIC HOT WATER PIPING
USING MULTIPLE MEGA-STORS