Water heating energy use is based on the number of bedrooms, fuel type, distribution system, water heater type, and conditioned floor area. Detailed calculation information is included in Appendix B.
Proposed Design
The water heating system is defined by the heater type (gas, electric resistance, or heat pump), tank type, dwelling-unit distribution type, efficiency (either UEF or recovery efficiency with the standby loss), tank volume, exterior insulation R-value (only for indirect), rated input, and tank location (for electric resistance and heat pump water heater only).
Heat pump water heaters are defined by energy factor, volume, and tank location or, for Northwest Energy Efficiency Alliance (NEEA) rated heat pumps, by selecting the specific heater brand, model, and tank location.
Water heater and tank types include:
- Consumer storage: ≤ 75,000 Btu/h gas/propane, ≤ 12 kW electric, or ≤ 24 amps heat pump, rated with UEF.
- Consumer instantaneous: ≤ 200,000 Btu/h gas or propane, or ≤ 12 kW electric. An instantaneous water heater is a water heater with an input rating of ≥ 4,000 Btu/h/gallon of stored water, rated with a UEF.
- Residential-duty commercial storage: > 75,000 Btu/h, ≤ 105,000 Btu/h gas/propane, ≤ 12 kW electric, ≤ 24 amps heat pump, and rated storage volume < 120 gallons, rated with a UEF.
- Residential-duty commercial instantaneous: ≤ 200,000 Btu/h gas/propane, ≤ 58.6 kW electric, rated storage volume ≤ 2 gallons, rated with a UEF.
- Commercial storage: > 75,000 Btu/h gas/propane, >105,000 Btu/h oil, or > 12 kW electric, rated with thermal efficiency and standby loss.
- Commercial instantaneous: >200,000 Btu/h gas/propane, > 12 kW electric. Instantaneous water heater is a water heater with an input rating of ≥ 4,000 Btu/h per gallon of stored water, rated with thermal efficiency.
- Heat pump water heater: ≤ 24 amps NEEA rating or rated with UEF.
- Mini-tank (modeled only in conjunction with an instantaneous gas water heater): a small electric storage buffering tank that may be installed downstream of an instantaneous gas water heater to mitigate delivered water temperatures (for example, cold water sandwich effect). If the standby loss of this aftermarket tank is not listed in the CEC appliance database, a standby loss of 35 W must be assumed.
- Indirect: a tank with no heating element or combustion device used in combination with a boiler or other device serving as the heating element.
- Boiler: a water boiler that supplies hot water, rated with thermal efficiency or AFUE.
Heater element type includes:
- Electric resistance.
- Gas.
- Heat pump.
Dwelling unit distribution system types include:
- Standard (all distribution pipes insulated).
- Point of use.
- Central parallel piping.
- Recirculation with non-demand control (continuous pumping).
- Recirculation with demand control, push button.
- Recirculation with demand control, occupancy/motion sensor.
- HERS-required pipe insulation, all lines.
- HERS-required central parallel piping.
- HERS-required recirculation, demand control, push button.
- HERS-required recirculation with demand control, occupancy/motion sensor.
Some distribution systems have an option to increase the amount of credit received if the option for HERS verification is selected. See Appendix B for the amount of credit and Reference Appendices, Residential Appendix Table RA2-1 for a summary of inspection requirements.
Distribution Compactness
Distribution compactness identifies the proximity between the water heater and use points. The distribution compactness of the water heating system must be specified. The choices include:
None.
Compact distribution basic credit.
Compact distribution expanded credit (HERS).
Once basic credit or expanded credit is specified, either the plan view fixture distances (to master bathroom, kitchen, and furthest fixture) will need to be input for the DHW system or, if the distances are unknown, allow a user input compactness factor to be used.
If the fixture distances are specified, the software will determine if the distances qualify for the credit.
If the fixture distances are not specified, compliance with the user input compactness factor will be verified on the CF2R where the actual fixture distances for the design will need to be specified.
Drain Water Heat Recovery
Drain water heat recovery (DWHR) is a system where the waste heat from shower drains is used to preheat the cold inlet water. The preheat water can be routed to the served shower, water heater, or both.
The user specifies the DWHR device for the water heating system. The rated efficiency of the DWHR device, the number of shower(s) served, and the configuration must be specified. The configuration choices include:
Equal flow to shower and water heater: The potable-side heat exchanger output feeds both the fixture and the water heater inlet. Potable and drain flow rates are equal, assuming no other simultaneous hot water draws.
Unequal flow to shower: The potable-side heat exchanger output feeds the inlet(s) of the water heater(s) that are part of the parent DHW system. (The inlet temperature is adjusted to reflect recovered heat.)
Unequal flow to water heater: The potable-side heat exchanger output feeds only the associated fixture.
Multiple DWHR devices can be used for a water heater system.
Drain water heat recovery is a HERS-verified measure.
The standard design is a single heat pump water heater with a 2.0 UEF. with compact distribution basic credit in Climate Zones 1 and 16, and a drain water heat recovery system in Climate Zone 16. In Climate Zone 16, the standard design DWHR has an exchanger efficiency of 0.65, serving 100 percent of showers, with an equal shower configuration.
If the proposed building has an attached garage, then the standard design HPWH location is the garage. If the proposed building does not have an attached garage, then the standard design HPWH location is in the conditioned space with the air inlet and outlet ducted to the outside.
In Climate Zones 3, 4, 13, and 14, if the proposed design is gas, then the standard design is a single gas or propane consumer instantaneous water heater for each dwelling unit. The single consumer instantaneous water heater is modeled with an input of 200,000 Btu/h, a tank volume of zero gallons, a high draw pattern, and a UEF meeting the minimum federal standards. The current minimum federal standard for a high-draw-pattern instantaneous water heater is 0.81 UEF. For buildings that are 500 square feet or less, if the proposed design is an instantaneous electric water heater, or an electric consumer storage water heater that is less than or equal to 20 gallons with point of use distribution, the standard design is the same.
When a water heating system has a solar thermal system to provide part of the water heating, the user enters information about the Solar Rating and Certification Corporation (SRCC) OG-100 approved collector (manufacturer, brand, model number), including details of the installation (azimuth, tilt).
Alternatively, the user can enter the OG-300 rated solar fraction for their specific climate zone