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Free tankless water heater savings calculator. Model annual gas or electric fuel cost for a storage tank versus a tankless unit on the same hot-water load using gallons per day, temperature rise, UEF, and a standby adder for tanks. Explore more in our energy and sustainability calculator category.
Last updated: April 18, 2026
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Efficiency & standby
Approximate extra fuel vs recovery-only for a tank (pilot, jacket loss, cycling). Tankless modeled without this adder.
Storage tank
$266
231 therms/yr
Tankless
$160
139 therms/yr
Estimated annual savings (tankless vs storage)
$106
≈ 40% of modeled storage fuel cost.
Planning note
Load
Larger gpd
Higher draw increases absolute savings when tankless efficiency and standby avoidance help.
Savings
Wider UEF spread
Replacing an older tank with poor UEF increases modeled savings potential.
Dial
Standby %
Increase standby percent when the tank sits hot most of the day.
Rates
$/kWh
Switch fuel type to electric and use your blended or TOU rate cautiously.
Climate
ΔT up
Northern climates with colder groundwater increase annual load.
Next
Bill tools
Pair with electric or gas bill calculators for full-home context.
Default gas scenario: modeled annual savings about $106 vs the storage tank path (positive means lower operating cost for tankless under these inputs).
Useful hot-water energy per year is estimated from gallons per day, 365 days, 8.34 pounds per gallon, and temperature rise. The storage path divides that energy by storage UEF and multiplies by one plus the standby percentage to approximate extra fuel beyond ideal recovery. The tankless path divides the same useful energy by tankless UEF without the standby multiplier. Fuel costs apply to each path’s input energy using therms for gas or kilowatt-hours for electricity.
Useful BTU/yr ≈ gpd × 365 × 8.34 × ΔTStorage fuel ≈ useful ÷ UEF_tank × (1 + standby%)Tankless fuel ≈ useful ÷ UEF_tanklessAdjust gallons per day and UEF to match your household and product labels.
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