Gas storage tank
Typical planning range: UEF about 0.60-0.70 for gas storage tanks. Default 0.64 is a typical non-condensing gas storage planning value; use your unit's EnergyGuide UEF if known.
$per therm
Default: 0.64
Water heater operating-cost comparison
An honest "what does it cost to run?" calculator for household hot water. Enter your own natural-gas and electric rates, adjust gallons and UEF, and compare annual operating energy cost.
User-supplied fuel pricesEIA heat-content constantsDOE and ENERGY STAR UEF citations
Compare annual cost to run
Enter your own utility rates, daily hot-water use, temperature rise, and UEF assumptions. Blank fuel prices are skipped.
Fuel prices are user-supplied. Placeholders are examples only, not current or national average prices.
Formula
usefulEnergyBTU = gallons × 8.33 lb/gal × ΔT°F × 1 BTU/(lb·°F)
annual cost = ((gallons/day × 365 × 8.33 lb/gal × ΔT°F × 1 BTU/(lb·°F)) ÷ UEF ÷ fuel BTU/unit) × user price/unit
gal/day
Default: ~64 gal/day - DOE
°F
Default: 70°F = 50°F -> 120°F
100,000 BTU/therm
Electric storage tank
Typical planning range: UEF about 0.90-0.95 for electric resistance storage tanks. Default 0.92 is a typical electric storage planning value; use the yellow EnergyGuide UEF if known.
$per kWh
Default: 0.92
Gas tankless
Typical planning range: UEF about 0.80-0.93 for gas tankless units. Default 0.87 is a midrange gas tankless planning value; tankless units avoid tank standby loss, but model UEF varies.
$per therm
Default: 0.87
Heat-pump water heater
Typical ENERGY STAR heat-pump water heater range: UEF about 3.3-4.1. Default 3.5 is a typical heat-pump water heater planning value; cold installation spaces reduce real-world performance.
$per kWh
Default: 3.5
Annual operating energy cost
Sorted from lowest to highest annual energy cost for the same hot-water load.
Enter at least one fuel price to compare annual water-heating energy cost.
Constants and sources
Default load assumptions
Typical daily hot-water use: 64 gal/day
DOE's average hot-water-usage table lists a total daily average of 64 gallons.
Source: DOE Energy Saver, Reduce Hot Water Use for Energy Savings
Temperature rise: 70 °F
Default planning assumption: 50°F incoming water heated to 120°F. Incoming water temperature varies by home and season.
Physical constants
Weight of water: 8.33 lb/gal
Rounded from USGS' 8.329 lb per gallon of tap water at 70°F.
Specific heat of water: 1 BTU/(lb·°F)
EIA defines one Btu as the heat needed to raise one pound of water by 1°F.
Source: U.S. Energy Information Administration (EIA), British thermal units
Fuel heat content
Natural gas: 100,000 BTU/therm
Reused from the heating-cost fuel registry: natural gas therm definition.
Source: U.S. Energy Information Administration (EIA), British thermal units
Electricity: 3,412 BTU/kWh
Reused from the heating-cost fuel registry: electricity heat content per kWh.
Source: U.S. Energy Information Administration (EIA), British thermal units
Propane: 91,452 BTU/gallon
Reused from the heating-cost fuel registry for cross-fuel transparency.
Heating oil: 137,380 BTU/gallon
Reused from the heating-cost fuel registry for cross-fuel transparency.
Source: U.S. Energy Information Administration (EIA), energy units and calculators
UEF defaults
Gas storage tank: 0.64 UEF
Default 0.64 is a typical non-condensing gas storage planning value; use your unit's EnergyGuide UEF if known.
Source: DOE Energy Saver water-heater UEF guidance; ENERGY STAR UEF overview
Electric storage tank: 0.92 UEF
Default 0.92 is a typical electric storage planning value; use the yellow EnergyGuide UEF if known.
Source: DOE Energy Saver water-heater UEF guidance; ENERGY STAR UEF overview
Gas tankless: 0.87 UEF
Default 0.87 is a midrange gas tankless planning value; tankless units avoid tank standby loss, but model UEF varies.
Source: DOE Energy Saver water-heater UEF guidance; ENERGY STAR UEF overview
Heat-pump water heater: 3.5 UEF
Default 3.5 is a typical heat-pump water heater planning value; cold installation spaces reduce real-world performance.
Source: ENERGY STAR, What is Uniform Energy Factor and Why Does it Matter?
Use the adjacent ProFix checks
This tool answers water-heater operating energy cost only. Use the related checks for space heating fuel cost, project-cost context, and repair decisions.
Frequently asked
Does this prove I should replace my water heater?
No. It compares annual operating energy cost for the same hot-water load using user-entered fuel prices and cited UEF assumptions. It does not include equipment, installation, maintenance, venting, electrical work, rebates, or your actual usage.
What is the physics formula?
The useful energy is usefulEnergyBTU = gallons × 8.33 lb/gal × ΔT°F × 1 BTU/(lb·°F). Annual cost then applies UEF, fuel heat content, and your own price per unit.
Where do the fuel heat-content constants come from?
The natural gas, electricity, propane, and heating-oil heat-content constants are reused from ProFix's heating-cost registry and cited to the U.S. Energy Information Administration.
Why can a heat-pump water heater have UEF above 1?
A heat-pump water heater moves heat from surrounding air into the tank instead of creating all heat with electric resistance. ENERGY STAR describes typical certified heat-pump water heaters around UEF 3.3 to 4.1, but cold installation spaces reduce performance.
Are the fuel prices current averages?
No. Fuel prices are intentionally user-supplied. Any placeholder in the form is only a prompt to enter your own bill rate or delivery quote.