Water Heater Energy Efficiency (EF/UEF) Savings Calculator

Compare your current and new water heater efficiency ratings (EF or UEF) to estimate annual energy consumption and cost savings.

Typical gas storage: 0.55–0.70 | Electric resistance: 0.90–0.95 | Heat pump: 2.0–4.0
ENERGY STAR gas tankless: 0.82+ | Heat pump: 2.0–4.0 | Condensing gas: 0.90+
DOE test draw pattern: 64 gal/day for a family of 4
U.S. avg natural gas ~$1.20/therm | Electric ~$0.16/kWh | Propane ~$2.50/gallon | Oil ~$4.00/gallon
U.S. average groundwater ~58°F; warmer climates 65–70°F
Recommended safe delivery temperature: 120°F

Formulas Used

1. Annual Hot Water Heat Load (BTU/year):

Qload = Gallons/day × 365 × 8.3454 lb/gal × 1 BTU/(lb·°F) × (Tout − Tin)

2. Annual Energy Input (fuel units/year):

Einput = Qload / EF  →  convert BTU to fuel units (÷ BTU/unit)

Where EF (Energy Factor) or UEF (Uniform Energy Factor) = useful energy output ÷ total energy input. A higher EF/UEF means less fuel consumed for the same hot water output.

3. Annual Cost:

Cost = Einput (units/yr) × Rate ($/unit)

4. Annual Savings:

Savings = Costcurrent − Costnew

Fuel Unit Conversions: Natural gas: 100,000 BTU/therm | Electric: 3,412 BTU/kWh | Propane: 91,452 BTU/gal | Fuel Oil: 138,500 BTU/gal

Assumptions & References

  • Water density used: 8.3454 lb/gallon (at ~60°F); specific heat of water: 1 BTU/(lb·°F).
  • Default daily draw of 64 gallons/day matches the DOE/FTC standardized test draw pattern used to rate EF/UEF on EnergyGuide labels.
  • EF (Energy Factor) is the legacy DOE metric (pre-2015); UEF (Uniform Energy Factor) is the current DOE metric (post-April 2015) per 10 CFR Part 430. Both represent useful energy output ÷ total energy input over a test cycle.
  • CO₂ emission factors: Natural gas 11.7 lbs/therm (EPA); U.S. average grid electricity 0.851 lbs/kWh (EPA eGRID 2022); Propane 12.68 lbs/gal; Fuel oil 22.4 lbs/gal.
  • Default cold water inlet temperature of 58°F is the U.S. national average groundwater temperature used in DOE test procedures.
  • Recommended hot water delivery temperature of 120°F per ASHRAE and CDC guidelines to balance scalding risk and Legionella prevention.
  • This calculator estimates water heating energy only; standby losses, pipe losses, and distribution system efficiency are captured within the EF/UEF rating itself.
  • References: DOE 10 CFR Part 430 Subpart B Appendix E (UEF test procedure); ENERGY STAR Water Heater Specification v4.0; EPA WaterSense; EIA Annual Energy Outlook.

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