Energy Efficiency (EF/UEF) Savings Calculator
Estimate your annual energy and cost savings when upgrading from an old water heater to a more efficient model using Energy Factor (EF) or Uniform Energy Factor (UEF) ratings.
Typical old gas storage: 0.54–0.62 | Electric storage: 0.90–0.95 | Heat pump: 2.0–3.5
Typical new gas condensing: 0.80–0.96 | Heat pump electric: 2.0–4.0 | Tankless gas: 0.82–0.96
Average household: ~64 gal/day (DOE standard); adjust for your household size
Natural gas: ~$1.10–$1.50/therm | Electric: ~$0.12–$0.18/kWh | Propane: ~$2.50–$3.50/gallon | Oil: ~$3.50–$5.00/gallon
Typical groundwater: 50–65°F depending on region
Recommended: 120°F (DOE); 140°F for dishwashers without internal heaters
Formulas Used
Annual Useful Heat Demand (BTU/yr):
Quseful = Gallons/day × 365 × 8.33 BTU/(gal·°F) × (Toutlet − Tinlet)
Annual Energy Input Required (fuel units/yr):
Einput = Quseful ÷ (EF × BTUper unit)
Annual Cost:
Cost = Einput × Rate ($/unit)
Annual Savings:
Savings = Costold − Costnew
Where EF (Energy Factor) or UEF (Uniform Energy Factor) = Useful Energy Output ÷ Total Energy Input over a standard test cycle.
Assumptions & References
- Water heat capacity: 8.33 BTU per gallon per °F (standard value for water at typical domestic temperatures).
- Fuel energy content: Natural gas = 100,000 BTU/therm; Electricity = 3,412 BTU/kWh; Propane = 91,502 BTU/gallon; Fuel Oil (#2) = 138,500 BTU/gallon.
- Default daily usage of 64 gallons/day is the DOE standard test draw pattern for water heaters (10 CFR Part 430, Appendix E).
- EF (Energy Factor) is the older DOE test metric; UEF (Uniform Energy Factor) is the current standard per DOE 10 CFR 430 (effective April 2017). Both represent efficiency as useful output ÷ total input energy.
- CO₂ emission factors: Natural gas ≈ 11.7 lbs/therm (EPA); Electricity ≈ 0.92 lbs/kWh (US average grid, EPA eGRID 2022); Propane ≈ 12.7 lbs/gallon (EPA); Fuel Oil ≈ 22.4 lbs/gallon (EPA).
- Savings are based on steady-state operation and do not account for standby losses beyond what is captured in the EF/UEF rating, installation costs, or rebates.
- References: DOE EERE Water Heater Basics; ENERGY STAR Water Heater Specification; EPA Emission Factors for Greenhouse Gas Inventories (2023).