Heat Pump Water Heater Calculator

This calculator estimates the thermal energy needed to heat your household's hot water (gallons per day × 8.34 BTU per gallon-°F × temperature rise, converted to kWh), then divides by each unit's Uniform Energy Factor (UEF) to get the energy it draws. A heat pump water heater moves heat rather than generating it, so its UEF of roughly 3.0–4.0 means it uses about a third of the electricity of a standard electric resistance tank (UEF ~0.92). Gas comparisons convert thermal demand into therms at the gas tank's UEF (~0.62 for standard atmospheric models). Both replacement paths assume your current unit is due for replacement, so the heat pump's investment is compared against installing a like-for-like conventional unit, with energy rates escalating annually. Note on incentives: the federal 25C credit that covered heat pump water heaters (30% up to $2,000) ended December 31, 2025; many state and utility rebates remain — enter what you qualify for in the Rebates field. CO₂ estimates use 0.855 lbs/kWh for grid electricity, 11.7 lbs/therm for natural gas, and 12.7 lbs/gallon for propane.