Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: Domestic Water Heating and Storage Equipment
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## Storage tanks installed in Seismic Design Category C and above shall be anchored using manufacturer-certified anchorage or anchorage details stamped by a Professional Engineer.
−### A storage tank over 50 gallons is heavy when full and becomes a life-safety hazard if it shifts or topples in a seismic event; anchorage is coordinated with the structural engineer rather than assumed from the tank pad alone. {note}
−
```datasheet
label: Seismic Design Category
…7 unchanged lines
```
+### A storage tank over 50 gallons is heavy when full and becomes a life-safety hazard if it shifts or topples in a seismic event; anchorage is coordinated with the structural engineer rather than assumed from the tank pad alone. {note}
+
## Equipment shall be rated for the ambient conditions of its installed location, including mechanical-room temperature extremes and any freeze exposure on the recirculation return.
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### The tank type is selected from water chemistry, heating method, and the authority having jurisdiction, and is the primary configuration decision for the storage system. {note}
+### The storage tank lining and construction shall be specified based on the project's water chemistry, heating method, and the authority having jurisdiction.
+
```datasheet
label: Storage tank lining / construction
…16 unchanged lines
### The storage tank may be heated directly by an integral source, indirectly through an internal coil, indirectly through an external heat exchanger, or by a heat-pump source; the direct-fired appliance itself is specified under [[sync/water-heaters]]. {note}
+### The storage tank heating method shall be specified, coordinated with the water heater or heat source serving the tank.
+
```datasheet
label: Tank heating method
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### A large tank paired with an undersized heater still delivers cold water during peak demand because the stored volume cannot be reheated fast enough; capacity is a function of both stored gallons and recovery, never stored gallons alone. {note}
−### Rule-of-thumb storage figures - on the order of 1.5 to 2.0 gallons per fixture unit for office and commercial, 8 to 12 gallons per hotel room, and 10 to 15 gallons per healthcare bed - may be used only for preliminary sizing and shall be verified by full calculation. {note}
+### Rule-of-thumb storage figures - on the order of 1.5 to 2.0 gallons per fixture unit for office and commercial, 8 to 12 gallons per hotel room, and 10 to 15 gallons per healthcare bed - may be used only for preliminary sizing and shall be verified by full calculation.
```datasheet
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### The tank may be vertical or horizontal; vertical orientation preserves thermal stratification and is preferred where floor area permits. {note}
+### The storage tank orientation shall be specified, using vertical orientation where floor area permits to preserve thermal stratification.
+
```datasheet
label: Tank orientation
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### The tank working pressure rating shall equal or exceed the maximum system pressure at the tank location, including any boosted-supply zones.
−### A tank operating above 30 psi requires the ASME Section VIII stamp; nearly all commercial storage applications fall above that threshold, so the stamp is effectively mandatory at commercial scale. {note}
−
```datasheet
label: Tank working pressure rating
…6 unchanged lines
```
+### A tank operating above 30 psi requires the ASME Section VIII stamp; nearly all commercial storage applications fall above that threshold, so the stamp is effectively mandatory at commercial scale. {note}
+
## Tank jacket insulation {note}
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### The master ASSE 1017 valve shall be set to deliver distribution water in the 120°F to 140°F band; 120°F is the common default, and the setpoint shall be raised toward 140°F where healthcare code requires maintaining an elevated distribution temperature.
−### Where a facility must maintain a minimum recirculation return temperature, the master valve outlet shall be set high enough that no return leg drops below that minimum at worst-case flow.
−
−### Setting the master valve at 120°F in a building required to hold 122°F in the recirculation loop is self-defeating - the mixed supply cannot keep the return above its floor; the master setpoint and the return floor are sized together. {note}
−
```datasheet
label: Master mixing valve outlet temperature
…6 unchanged lines
```
+### Where a facility must maintain a minimum recirculation return temperature, the master valve outlet shall be set high enough that no return leg drops below that minimum at worst-case flow.
+
+### Setting the master valve at 120°F in a building required to hold 122°F in the recirculation loop is self-defeating - the mixed supply cannot keep the return above its floor; the master setpoint and the return floor are sized together. {note}
+
## Point-of-use temperature limit {note}
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### The temperature control interface may be a standalone aquastat, an integrated electronic controller, or a connection to the Building Automation System (BAS). {note}
+### The temperature control interface for the storage system's temperature setpoint shall be specified.
+
```datasheet
label: Temperature control interface
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### Recirculation shall be controlled by demand-based control (push-button or occupancy), a time clock, or continuous circulation with a temperature floor, in accordance with ASHRAE 188 and ASHRAE 90.1.
−### Aquastat-only control is the single most common Legionella pitfall in recirculation design; ASHRAE 188 effectively condemns it, and the demand or timed alternatives below keep the loop above the growth band. {note}
−
```datasheet
label: Recirculation control method
…7 unchanged lines
```
+### Aquastat-only control is the single most common Legionella pitfall in recirculation design; ASHRAE 188 effectively condemns it, and the demand or timed alternatives below keep the loop above the growth band. {note}
+
## Demand-controlled or time-clock recirculation shall be provided where required by ASHRAE 90.1 for systems above the threshold capacity; constant-speed continuous pumping shall not be used where that section applies.
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### The recirculation pump shall be an in-line or wet-rotor type, sized for the piping heat-loss load at a design loop temperature drop of 10°F to 20°F.
−### Variable-speed recirculation pumps should be specified where demand-controlled operation or energy code compliance favors them. {note}
−
```datasheet
label: Recirculation pump type
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```
+### Variable-speed recirculation pumps should be specified where demand-controlled operation or energy code compliance favors them. {note}
+
## Return piping layout {note}
### The return piping may be arranged as a single main loop or as branch returns; branch returns improve delivery time at distant fixtures at the cost of additional balancing. {note}
+### The recirculation return piping layout shall be specified as a single main loop or branch returns.
+
```datasheet
label: Recirculation return layout
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### The expansion tank volume shall be sized using the manufacturer nomograph or calculation accounting for actual system volume, operating pressure, pre-charge pressure, and the temperature rise from supply to storage temperature; a rule-of-thumb volume shall not be substituted for the calculation.
−### The expansion tank shall be sized so that system pressure does not exceed 80% of the T&P relief valve set pressure under worst-case expansion.
−
−### A rule of thumb of roughly one gallon of expansion volume per fifty gallons of system water gives a starting point only; undersizing from rule-of-thumb alone is a frequent defect because it ignores operating and pre-charge pressure. {note}
−
```datasheet
label: Expansion tank volume
…6 unchanged lines
```
+### The expansion tank shall be sized so that system pressure does not exceed 80% of the T&P relief valve set pressure under worst-case expansion.
+
+### A rule of thumb of roughly one gallon of expansion volume per fifty gallons of system water gives a starting point only; undersizing from rule-of-thumb alone is a frequent defect because it ignores operating and pre-charge pressure. {note}
+
# Heat Exchangers for Indirect Heating {toc}
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### Brazed-plate exchangers are compact, efficient, and lower cost but are not cleanable, while shell-and-tube exchangers tolerate higher pressures and temperatures and can be opened for cleaning; shell-and-tube is preferred for steam service and where periodic cleaning is anticipated. {note}
+### The heat exchanger type shall be specified, using a shell-and-tube exchanger where steam service or periodic cleaning is anticipated.
+
```datasheet
label: Heat exchanger type
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### The heating medium for the indirect exchanger may be low-pressure steam, high-temperature hot water, or condenser hot water; the medium determines the exchanger pressure and temperature rating. {note}
+### The heating medium supplied to the indirect heat exchanger shall be specified.
+
```datasheet
label: Heating medium
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# Heat-Pump Storage Configuration {toc}
−## Where a heat-pump water heater serves the storage system, the storage tank shall be configured for the lower temperature differential and longer recovery characteristic of heat-pump operation. {note}
+## Where a heat-pump water heater serves the storage system, the storage tank shall be configured for the lower temperature differential and longer recovery characteristic of heat-pump operation.
### Heat-pump storage configurations typically require larger stored volume than equivalent direct-fired systems because recovery is slower; storage capacity shall reflect the heat-pump recovery rate rather than a direct-fired recovery assumption.
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## Recirculation supply and return piping shall be insulated to the minimum thickness required by ASHRAE 90.1 for the fluid temperature and pipe size, with not less than 1 inch of insulation on 3/4 inch recirculation return pipe.
−### Insulating the return leg as well as the supply is what keeps the recirculation return above its temperature floor; leaving the return bare defeats both the energy and the Legionella objectives. {note}
−
```datasheet
label: Recirculation pipe insulation thickness
…6 unchanged lines
```
+### Insulating the return leg as well as the supply is what keeps the recirculation return above its temperature floor; leaving the return bare defeats both the energy and the Legionella objectives. {note}
+
# Testing {toc}
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- Heat exchanger gasket and seal set
```