+---
+title: Domestic Water Heating and Storage Equipment
+category: Plumbing
+toc_depth: 3
+description: >
+ When to use: specifying domestic hot water storage and distribution accessory
+ equipment on commercial, institutional, and multi-family residential plumbing
+ systems - unfired storage tanks (glass-lined, stone-lined, stainless, copper-lined),
+ thermostatic mixing valves (system and point-of-use), hot-water recirculation pumps
+ and controls, potable thermal expansion tanks, indirect-heating heat exchangers
+ (brazed-plate, shell-and-tube), heat-pump storage configurations, and integral
+ accessories (aquastats, temperature-pressure relief valves, drain valves) on new
+ construction and major renovation with engineered plumbing documents.
+ Not intended for: water heater appliances themselves (sync/water-heaters);
+ cold-water pressure boosting (sync/domestic-water-booster-pumps); general
+ distribution valves, strainers, and specialties (sync/domestic-water-piping-specialties);
+ circulating pumps specified generically (sync/plumbing-pumps); backflow preventers
+ (sync/backflow-prevention); solar thermal collectors, hydronic space-heating
+ equipment and boilers, sewage/stormwater pump stations (sync/packaged-pump-stations),
+ and radiant panels (sync/radiant-heating-and-cooling-panels).
+---
+
+# Scope {toc}
+
+## This standard covers the storage, tempering, recirculation, and indirect-heating accessories that surround a domestic hot water source and deliver tempered potable water safely to the fixtures it serves. {note}
+
+## The central design tension this standard resolves is the gap between storage temperature and delivery temperature. {note}
+
+### Water must be stored hot enough to suppress Legionella growth - 140°F (60°C) is the commercial floor under ASHRAE 188 - yet delivered cool enough to prevent scalding, with a 120°F (49°C) ceiling at most fixtures and lower at care-facility showers. Bridging that gap with thermostatic mixing and a properly controlled recirculation loop is the recurring engineering problem these products solve, and most of the requirements below exist to enforce one side of it without sacrificing the other.
+
+## Included equipment {note}
+
+### The following equipment is included within this standard: {note}
+- Unfired hot water storage tanks: glass-lined (porcelain enamel), stone-lined (cement-lined), stainless steel (Type 304 or 316L), and copper-lined
+- Thermostatic mixing valves: system-level (master) valves to ASSE 1017 and point-of-use or fixture valves to ASSE 1070 / ASSE 1069
+- Domestic hot water recirculation pumps, their controls, and the return piping arrangement
+- Potable-water thermal expansion tanks (bladder/diaphragm type)
+- Heat exchangers for indirect water heating: brazed-plate and shell-and-tube
+- Heat-pump water heater storage configurations (integrated and remote storage)
+- Integral accessories: aquastats, temperature-pressure (T&P) relief valves, and drain valves serving the storage and distribution system
+
+## Excluded equipment {note}
+
+### The water heater appliance itself - the heat-generating device, whether gas, electric, oil, tankless/instantaneous, or a packaged heat-pump unit - is specified under [[sync/water-heaters]]; this standard governs only the storage vessel, tempering, recirculation, and indirect-heating accessories around it. {note}
+
+### Domestic cold-water pressure boosting is specified under [[sync/domestic-water-booster-pumps]]. {note}
+
+### General distribution valves, strainers, unions, and piping specialties on the domestic water system are specified under [[sync/domestic-water-piping-specialties]]; only the mixing valves, T&P relief valves, and drain valves integral to the storage/distribution accessories are included here. {note}
+
+### Circulating pumps specified under a general plumbing pump section are governed by [[sync/plumbing-pumps]]; the dedicated domestic hot water recirculation pump and its Legionella-aware control logic are retained here. {note}
+
+### Backflow preventers protecting the potable supply are specified under [[sync/backflow-prevention]]; this standard only requires the thermal expansion control that becomes necessary once a backflow preventer or check valve creates a closed system. {note}
+
+### Solar thermal collectors and solar energy heating systems, hydronic space-heating equipment and boilers, sewage and stormwater packaged pump stations (see [[sync/packaged-pump-stations]]), and radiant heating or cooling panels (see [[sync/radiant-heating-and-cooling-panels]]) are outside this standard's boundary. {note}
+
+# Referenced Standards {toc}
+
+## Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited or the authority having jurisdiction has adopted a different edition.
+
+## Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+
+| Standard | Title |
+|----------|-------|
+| ASME BPVC Section VIII, Div. 1 | Rules for Construction of Pressure Vessels |
+| ANSI/ASSE 1017 | Performance Requirements for Temperature Actuated Mixing Valves for Hot Water Distribution Systems |
+| ANSI/ASSE 1069 | Performance Requirements for Automatic Temperature Control Mixing Valves |
+| ANSI/ASSE 1070 | Performance Requirements for Water Temperature Limiting Devices |
+| ANSI/ASSE 1016 | Performance Requirements for Automatic Compensating Valves for Individual Showers and Tub/Shower Combinations |
+| NSF/ANSI 61 | Drinking Water System Components - Health Effects |
+| NSF/ANSI 372 | Drinking Water System Components - Lead Content |
+| NSF 5 | Water Heaters, Hot Water Supply Boilers, and Heat Recovery Equipment |
+| UL 174 | Household Electric Storage Tank Water Heaters |
+| UL 1453 | Electric Booster and Commercial Storage Tank Water Heaters |
+| ASHRAE 188 | Legionellosis: Risk Management for Building Water Systems |
+| ASHRAE 90.1 | Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings |
+| ASHRAE Handbook - HVAC Applications | Service Water Heating (Chapter 50) |
+| IPC | International Plumbing Code (Chapter 5; Sections 504, 607) |
+| IMC | International Mechanical Code (Chapter 10) |
+| NFPA 99 | Health Care Facilities Code |
+
+# Submittals {toc}
+
+## Action submittals {note}
+
+### The Contractor shall submit the following action submittals for review before fabrication, ordering, or installation:
+- Product data for each storage tank, mixing valve, recirculation pump, expansion tank, and heat exchanger, including capacity, pressure rating, materials of construction, and listing marks
+- Shop drawings showing tank dimensions, connection sizes and locations, lifting and anchorage points, and the recirculation return connection elevation on the tank
+- Storage tank capacity and recovery calculation, including the peak-hour demand basis and the associated water heater recovery rate
+- Thermal expansion tank sizing calculation using the manufacturer nomograph, stating system volume, inlet pressure, pre-charge pressure, temperature rise, and maximum allowable working pressure
+- Mixing valve schedule listing each valve's standard (ASSE 1017, 1069, or 1070), set outlet temperature, flow range, and pipe size
+- Recirculation system schematic showing pump selection point, control method, and return loop arrangement
+- NSF/ANSI 61 and NSF/ANSI 372 certification for every wetted component
+- Seismic anchorage details, manufacturer-certified or stamped by a Professional Engineer, for projects in Seismic Design Category C and above
+
+```datasheet
+label: Action submittals required
+type: checkbox
+options:
+ - Product data (tanks, valves, pumps, expansion tanks, heat exchangers)
+ - Shop drawings with connection and anchorage points
+ - Storage capacity and recovery calculation
+ - Expansion tank sizing calculation (nomograph)
+ - Mixing valve schedule with set temperatures
+ - Recirculation system schematic and control narrative
+ - NSF/ANSI 61 and 372 certification
+ - Seismic anchorage details (SDC C and above)
+default:
+ - Product data (tanks, valves, pumps, expansion tanks, heat exchangers)
+ - Shop drawings with connection and anchorage points
+ - Storage capacity and recovery calculation
+ - Expansion tank sizing calculation (nomograph)
+ - Mixing valve schedule with set temperatures
+ - Recirculation system schematic and control narrative
+ - NSF/ANSI 61 and 372 certification
+```
+
+## Informational submittals {note}
+
+### The Contractor shall submit the following informational submittals:
+- ASME Section VIII data report (Form U-1 or U-1A) for each ASME-stamped vessel
+- Factory hydrostatic and dielectric test certificates
+- Manufacturer installation, operation, and maintenance instructions
+- Statement of energy performance demonstrating compliance with ASHRAE 90.1 for the service water heating equipment
+
+```datasheet
+label: Informational submittals required
+type: checkbox
+options:
+ - ASME Section VIII data report (U-1 / U-1A)
+ - Factory hydrostatic and dielectric test certificates
+ - Manufacturer installation and O&M instructions
+ - ASHRAE 90.1 energy performance statement
+default:
+ - ASME Section VIII data report (U-1 / U-1A)
+ - Factory hydrostatic and dielectric test certificates
+ - Manufacturer installation and O&M instructions
+ - ASHRAE 90.1 energy performance statement
+```
+
+## Closeout submittals {note}
+
+### The Contractor shall submit the following closeout submittals before final acceptance:
+- Operation and maintenance manuals compiling all product data, test reports, and warranty documents
+- Recorded mixing valve set temperatures and recirculation control setpoints as commissioned
+- Water management plan documentation interface where ASHRAE 188 applies
+- Warranty certificates for each tank, valve, pump, and heat exchanger
+
+```datasheet
+label: Closeout submittals required
+type: checkbox
+options:
+ - Operation and maintenance manuals
+ - As-commissioned setpoint record
+ - ASHRAE 188 water management plan interface documentation
+ - Warranty certificates
+default:
+ - Operation and maintenance manuals
+ - As-commissioned setpoint record
+ - Warranty certificates
+```
+
+# Quality Assurance {toc}
+
+## All wetted components shall be certified to NSF/ANSI 61 for drinking water health effects.
+
+## All wetted components shall comply with NSF/ANSI 372 for lead content, satisfying the federal lead-free requirement of the Safe Drinking Water Act as amended.
+
+## Storage tanks and expansion tanks with an operating pressure above 30 psi shall be constructed and stamped in accordance with ASME Boiler and Pressure Vessel Code, Section VIII, Division 1.
+
+## System-level (master) thermostatic mixing valves shall be listed to ANSI/ASSE 1017.
+
+## Point-of-use and fixture-level tempering valves shall be listed to ANSI/ASSE 1070, and individual-fixture automatic control mixing valves shall be listed to ANSI/ASSE 1069 where applied.
+
+## Commercial electric storage tank heaters integral to a storage configuration shall be listed to UL 1453; residential-scale electric storage tank units shall be listed to UL 174.
+
+## The lead-free and NSF 61 obligations are routinely overlooked on heat exchanger plate and mixing valve internal selections; both apply to every component that contacts potable water, not only the visible tank. {note}
+
+## Where the facility is covered by ASHRAE 188, the storage temperature, recirculation return temperature, and mixing valve setpoints specified here shall be consistent with the building water management plan. {note}
+
+# Environmental and Service Conditions {toc}
+
+## The selection of tank lining is governed first by water chemistry, and a lining mismatch is the most common cause of premature tank failure. {note}
+
+### Glass-lined (porcelain enamel) tanks shall not be specified for aggressive water - low pH or high chloride content - without confirming compatibility with the local water analysis; stainless steel (Type 316L) or stone-lined construction shall be specified for aggressive water chemistry.
+
+### The Contractor shall obtain the local potable water analysis, including pH and chloride concentration, and confirm tank lining compatibility before ordering.
+
+```datasheet
+label: Governing water chemistry
+type: select
+options:
+ - Benign municipal supply (neutral pH, low chloride)
+ - Moderately aggressive (slightly low pH or moderate chloride)
+ - Aggressive (low pH and/or high chloride)
+ - Softened water (elevated sodium)
+default: Benign municipal supply (neutral pH, low chloride)
+```
+
+## 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
+type: select
+options:
+ - A or B (no seismic anchorage required)
+ - C
+ - D
+ - E or F
+default: C
+```
+
+## 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.
+
+# Storage Tanks {toc}
+
+## Storage tank type {note}
+
+### 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}
+
+```datasheet
+label: Storage tank lining / construction
+type: radio
+options:
+ - Glass-lined (porcelain enamel)
+ - Stone-lined (cement-lined)
+ - Stainless steel Type 304
+ - Stainless steel Type 316L
+ - Copper-lined
+default: Glass-lined (porcelain enamel)
+```
+
+### Glass-lined tanks shall be furnished with a sacrificial or powered anode rod, and the anode shall be accessible for inspection and replacement.
+
+### Stainless steel tanks shall be Type 316L where chloride content is elevated, and Type 304 is acceptable only for benign water chemistry.
+
+## Heating method {note}
+
+### 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}
+
+```datasheet
+label: Tank heating method
+type: radio
+options:
+ - Direct-fired (integral gas or electric element)
+ - Indirect - internal heating coil (steam or hot water)
+ - Indirect - external heat exchanger (brazed-plate or shell-and-tube)
+ - Heat-pump indirect
+default: Indirect - external heat exchanger (brazed-plate or shell-and-tube)
+```
+
+## Storage capacity {note}
+
+### Storage capacity shall be determined by a peak-hour demand calculation per the ASHRAE Handbook - HVAC Applications or an equivalent ASPE method, and shall be coordinated with the recovery rate of the associated water heater.
+
+### 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}
+
+```datasheet
+label: Storage tank capacity
+type: range
+unit: gallon
+min: 30
+max: 5000
+step: 10
+default: 500
+```
+
+## Tank orientation {note}
+
+### The tank may be vertical or horizontal; vertical orientation preserves thermal stratification and is preferred where floor area permits. {note}
+
+```datasheet
+label: Tank orientation
+type: radio
+options:
+ - Vertical
+ - Horizontal
+default: Vertical
+```
+
+## Working pressure {note}
+
+### 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
+type: radio
+options:
+ - 125 psi
+ - 150 psi
+default: 125 psi
+unit: psi
+```
+
+## Tank jacket insulation {note}
+
+### The tank shall be furnished with factory jacket insulation meeting or exceeding the minimum standby-loss requirement of ASHRAE 90.1 for the equipment class.
+
+```datasheet
+label: Tank jacket insulation R-value
+type: range
+unit: hr·ft²·°F/Btu
+min: 12
+max: 25
+step: 1
+default: 16
+```
+
+## Tank connections {note}
+
+### Tank connections shall be provided for cold inlet, hot outlet, recirculation return, T&P relief, drain, anode access, and temperature sensing as applicable to the heating method.
+
+### The recirculation return connection shall enter near the bottom of the tank, not the top.
+
+### Returning cooled water to the top of the tank disrupts stratification and reduces the effective hot volume; the cooler return belongs at the bottom where it is reheated before rising. {note}
+
+# Thermostatic Mixing and Temperature Control {toc}
+
+## Mixing valve tiers {note}
+
+### Most buildings require two tiers of tempering: a master ASSE 1017 valve at the tank outlet to set distribution temperature, and point-of-use ASSE 1070 valves at fixtures to enforce the scald limit. {note}
+
+### A single central mixing valve in a large building shall not be relied upon as the sole scald protection, because distribution and reheating can allow delivery temperatures above 120°F at remote fixtures.
+
+```datasheet
+label: Mixing valve configuration
+type: radio
+options:
+ - Single master ASSE 1017 valve at tank outlet
+ - Master ASSE 1017 valve plus zone valves
+ - Master ASSE 1017 valve plus point-of-use ASSE 1070 valves
+ - Master, zone, and point-of-use valves (full three-tier)
+default: Master ASSE 1017 valve plus point-of-use ASSE 1070 valves
+```
+
+## Storage temperature setpoint {note}
+
+### The storage temperature setpoint shall be not less than 140°F (60°C) for commercial and institutional systems to suppress Legionella growth per ASHRAE 188; 120°F (49°C) is permitted only for residential systems not covered by a water management plan.
+
+```datasheet
+label: Storage temperature setpoint
+type: range
+unit: °F
+min: 120
+max: 160
+step: 5
+default: 140
+```
+
+## Master mixing valve outlet {note}
+
+### 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
+type: range
+unit: °F
+min: 120
+max: 140
+step: 2
+default: 120
+```
+
+## Point-of-use temperature limit {note}
+
+### Point-of-use ASSE 1070 tempering valves shall limit fixture outlet temperature to a maximum of 120°F (49°C).
+
+### Shower valves in assisted-living, memory-care, and similar care facilities shall limit outlet temperature to 105°F (41°C) in accordance with care-facility practice and ASSE 1016 / 1070 guidance.
+
+```datasheet
+label: Fixture-level outlet temperature limit
+type: radio
+options:
+ - 120°F (49°C) maximum - general fixtures
+ - 110°F (43°C) - public lavatories
+ - 105°F (41°C) - care-facility and accessible showers
+default: 120°F (49°C) maximum - general fixtures
+unit: °F
+```
+
+## Control interface {note}
+
+### The temperature control interface may be a standalone aquastat, an integrated electronic controller, or a connection to the Building Automation System (BAS). {note}
+
+```datasheet
+label: Temperature control interface
+type: radio
+options:
+ - Standalone aquastat
+ - Integrated electronic controller
+ - BAS integration
+default: Integrated electronic controller
+```
+
+# Recirculation System {toc}
+
+## Recirculation control method {note}
+
+### A dedicated, continuously running recirculation pump controlled only by an aquastat shall not be specified, because the pump stops once setpoint is reached and the stagnant water cools into the 77°F to 113°F Legionella growth band before the next call.
+
+### 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
+type: radio
+options:
+ - Demand-controlled (push-button or occupancy sensor)
+ - Time clock with temperature floor
+ - Continuous circulation with temperature floor
+ - Aquastat-only (not permitted)
+default: Demand-controlled (push-button or occupancy sensor)
+```
+
+## 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.
+
+## Recirculation return temperature {note}
+
+### The recirculation system shall be designed to maintain a return temperature of not less than 122°F (50°C) at the point of return to the heat source, in accordance with IPC Section 607.2, to prevent Legionella amplification.
+
+```datasheet
+label: Minimum recirculation return temperature
+type: range
+unit: °F
+min: 120
+max: 130
+step: 1
+default: 122
+```
+
+## Recirculation pump selection {note}
+
+### 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
+type: radio
+options:
+ - Fixed-speed wet-rotor
+ - Variable-speed wet-rotor
+ - In-line with external motor
+default: Variable-speed wet-rotor
+```
+
+```datasheet
+label: Recirculation pump design flow
+type: range
+unit: GPM
+min: 1
+max: 10
+step: 0.5
+default: 4
+```
+
+```datasheet
+label: Recirculation pump design head
+type: range
+unit: ft WC
+min: 5
+max: 25
+step: 1
+default: 12
+```
+
+## 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}
+
+```datasheet
+label: Recirculation return layout
+type: radio
+options:
+ - Single main loop
+ - Branch returns (multiple return legs)
+default: Single main loop
+```
+
+# Thermal Expansion Control {toc}
+
+## A potable-water thermal expansion tank shall be provided wherever a pressure-reducing valve, backflow preventer, or check valve on the cold-water supply creates a closed system, in accordance with IPC Section 607.3.
+
+### Thermal expansion control is routinely missed when a backflow preventer is added late in design and the supply quietly becomes a closed system; the requirement attaches to the closed condition, not to any single device. {note}
+
+## The expansion tank shall be a bladder or diaphragm type with all wetted surfaces certified to NSF/ANSI 61, and shall be factory pre-charged.
+
+## The expansion tank pre-charge pressure shall be set to match the cold-water supply pressure at the tank location.
+
+```datasheet
+label: Expansion tank pre-charge pressure
+type: range
+unit: psi
+min: 40
+max: 80
+step: 5
+default: 60
+```
+
+## Expansion tank volume {note}
+
+### 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
+type: range
+unit: gallon
+min: 2
+max: 80
+step: 2
+default: 8
+```
+
+# Heat Exchangers for Indirect Heating {toc}
+
+## Heat exchanger type {note}
+
+### Where the tank is heated indirectly by an external exchanger, the choice between brazed-plate and shell-and-tube is driven by the heating medium and maintenance access. {note}
+
+### 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}
+
+```datasheet
+label: Heat exchanger type
+type: radio
+options:
+ - Brazed-plate (stainless plates)
+ - Shell-and-tube, U-tube
+ - Shell-and-tube, straight-tube
+default: Brazed-plate (stainless plates)
+```
+
+## Heating medium {note}
+
+### 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}
+
+```datasheet
+label: Heating medium
+type: radio
+options:
+ - Low-pressure steam
+ - High-temperature hot water
+ - Standard hydronic hot water
+default: Standard hydronic hot water
+```
+
+## Shell-and-tube exchangers in steam service shall be protected by a steam separator, or the specification shall state a maximum allowable particulate level, where steam quality is unknown.
+
+### Wet or dirty steam fouls a tube bundle quickly; specifying a separator or a particulate limit prevents the most common shell-and-tube maintenance failure. {note}
+
+## All heat exchanger plates, tubes, and wetted surfaces in contact with potable water shall be certified to NSF/ANSI 61 and shall comply with NSF/ANSI 372.
+
+## Heat exchanger capacity {note}
+
+### The heat exchanger shall be sized for the peak heating load required to maintain storage setpoint at the design recovery rate.
+
+```datasheet
+label: Heat exchanger rated capacity
+type: range
+unit: MBH
+min: 20
+max: 500
+step: 10
+default: 200
+```
+
+# 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}
+
+### 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.
+
+## Heat-pump storage tanks shall be sized in the 50 to 120 gallon range for residential and light-commercial applications, with capacity confirmed by the peak-hour calculation.
+
+```datasheet
+label: Heat-pump storage tank capacity
+type: range
+unit: gallon
+min: 50
+max: 120
+step: 10
+default: 80
+```
+
+## A supplemental electric resistance element should be provided for peak demand backup where the heat-pump recovery alone cannot meet the peak-hour load. {note}
+
+# Accessories and Safety Devices {toc}
+
+## Each storage tank shall be furnished with a temperature-pressure (T&P) relief valve in accordance with IPC Section 504.4.
+
+## The T&P relief valve discharge shall be piped full-size to an approved termination in accordance with IPC Section 504.6, without valves or reductions in the discharge line.
+
+## Each tank shall be furnished with a full-port drain valve at the lowest point to permit complete draining and sediment flushing.
+
+## Aquastats and temperature sensors furnished as integral accessories shall be rated for the storage temperature and located to read representative tank temperature.
+
+# Insulation {toc}
+
+## 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
+type: range
+unit: inch
+min: 1
+max: 2
+step: 0.5
+default: 1
+```
+
+# Testing {toc}
+
+## ASME-stamped storage and expansion tanks shall be factory hydrostatically tested at 1.5 times the maximum allowable working pressure, and the test certificate shall be submitted.
+
+## Glass-lined tanks shall be factory dielectric-tested to verify lining integrity, and the test certificate shall be submitted.
+
+## Each thermostatic mixing valve shall carry documentation of flow and temperature performance per its listed ASSE 1017, 1069, or 1070 test procedure.
+
+## After installation, the Contractor shall verify and record the master mixing valve outlet temperature, each point-of-use valve outlet temperature, and the recirculation return temperature under design flow.
+
+## The Contractor shall demonstrate that the recirculation return temperature is maintained at or above the specified minimum at the most remote return leg.
+
+# Installation {toc}
+
+## Equipment shall be installed in accordance with the manufacturer's instructions and the adopted plumbing and mechanical codes.
+
+## Storage tanks shall be set on a level housekeeping pad or stand rated for the full operating weight of the tank, and anchored as required by the Seismic Design Category.
+
+## Clearances shall be maintained around each tank, valve, and exchanger for anode replacement, tube cleaning, valve servicing, and code-required access.
+
+## The recirculation pump shall be installed with isolation valves and a check valve to permit servicing without draining the loop.
+
+## Equipment locations, routing of recirculation mains, and the extent of the return loop shall be installed as shown on the drawings. [[drawing: mechanical-room equipment layout]]
+
+## Dielectric isolation shall be provided at connections between dissimilar metals to prevent galvanic corrosion.
+
+# Delivery, Storage, and Handling {toc}
+
+## Equipment shall be delivered in the manufacturer's original packaging with listing labels and connection protection intact.
+
+## Tanks and exchangers shall be stored upright and protected from weather, dust, and physical damage until installation.
+
+## Lifting shall use the manufacturer's designated lifting points; slings shall not be passed around connection nozzles or trim.
+
+# Warranty {toc}
+
+## The storage tank shall carry a manufacturer's warranty against tank and lining failure of not less than the period scheduled for the project.
+
+## Mixing valves, recirculation pumps, expansion tanks, and heat exchangers shall carry the manufacturer's standard warranty, and the warranty certificates shall be submitted at closeout.
+
+```datasheet
+label: Storage tank warranty period
+type: radio
+options:
+ - 3 years
+ - 5 years
+ - 6 years
+ - 10 years
+default: 6 years
+```
+
+# Spare Parts {toc}
+
+## The Contractor shall furnish spare anode rods for each glass-lined tank, sized and threaded for the installed tanks.
+
+## The Contractor shall furnish one spare thermostatic cartridge or repair kit for each model and size of mixing valve installed.
+
+## The Contractor shall furnish manufacturer-recommended gaskets and seals for each heat exchanger to support the first scheduled servicing.
+
+```datasheet
+label: Spare parts to be furnished
+type: checkbox
+options:
+ - Spare anode rods (one per glass-lined tank)
+ - Mixing valve cartridge / repair kit (one per model and size)
+ - Heat exchanger gasket and seal set
+ - Spare T&P relief valve (one per tank model)
+default:
+ - Spare anode rods (one per glass-lined tank)
+ - Mixing valve cartridge / repair kit (one per model and size)
+ - Heat exchanger gasket and seal set
+```