# Domestic Hot Water¶

## Determining the primary water heating system¶

HPXML allows for the specification of several WaterHeatingSystem elements. HEScore only allows one to be specified. If there are more than one water heaters present in the HPXML file, the one that serves the largest fraction of the the load is selected based on the value of FractionDHWLoadServed. If not all of the WaterHeatingSystem elements have FractionDHWServed subelements (or if none of them do), the first WaterHeatingSystem is selected.

## Water heater type¶

The water heater type is mapped from HPXML to HEScore accordingly:

HPXML to HEScore water heater type mapping
HPXML HEScore
WaterHeaterType DHW Category DHW Type
storage water heater unit storage
dedicated boiler with storage tank
instantaneous water heater unit tankless
heat pump water heater unit heat_pump
space-heating boiler with storage tank combined indirect
space-heating boiler with tankless coil combined tankless_coil

The fuel type is mapped according to the same mapping used in Primary Heating System Fuel mapping.

## Water heating efficiency¶

If the WaterHeating/UniformEnergyFactor element exists, that is passed to HEScore with an efficiency method of “uef”. Otherwise if the WaterHeatingSystem/EnergyFactor element exists, that energy factor is sent to HEScore along with an efficiency method of “user”, which tells it that to interpret it as a traditional energy factor. When an energy factor cannot be found, HEScore can accept the year the equipment was installed and estimate the efficiency based on that. The year is retrieved from the YearInstalled element, and if that is not present the ModelYear element.

If the DHW type is tankless, only energy factor or unified energy factor could be used to describe efficiency, the estimation based on installed year is no longer available.