Running cost calculator
Quick answer
Payback is the extra upfront cost divided by the annual saving. A heat pump water heater at $1,100 against a $550 resistance tank saves roughly $400 a year at typical use and electricity prices, which pays back the $550 difference in about 16 months.
Result
Put the INSTALLED cost difference into the upfront figure, not the sticker difference. A heat pump water heater often needs a condensate drain and 700 cubic feet of surrounding air, and a tankless retrofit often needs a larger gas line and a new vent, and those are where the real difference sits.
The formula
Annual saving = cost at the old UEF - cost at the new UEF. Payback years = extra upfront cost / annual saving.
This is simple payback with no discount rate and no fuel price escalation, which is the honest way to present it: adding assumptions about future energy prices makes the number look more precise while making it less reliable. Note also that the upfront difference should include installation, and a heat pump water heater often costs more to install than it does to buy.
The figures above are computed with these exact inputs: Fuel, same for both electricResistance, Current unit UEF 0.92, New unit UEF 3.5, Fuel price per unit 0.16 $, Extra upfront cost 550 $, Hot water per day 55 gal, Temperature rise 70 F.
Some of these are published test procedures or code tables and some are planning conventions. They are not the same kind of number, so each one is labeled.
| Assumption | Kind | Where it comes from |
|---|---|---|
| DOE Uniform Energy Factor | Published standard | DOE Uniform Energy Factor, measured over a standard daily draw pattern and including standby loss |
| Doe Daily Draw: 55 | Convention | Daily hot water use assumed for the annual cost figure. Actual household use varies widely and this is the input to change first |
| Water Weight: 8.33 | Published standard | Published density of water at 60 F, 8.33 lb per gallon |
Every card below is in the page source. The calculator re-ranks them against your numbers and marks anything that falls short of what you just calculated.
The lowest price of entry into a heat pump water heater in this catalog, and Energy Star listed, which means its efficiency figure was measured against the DOE test procedure rather than claimed.
Best for: A first heat pump water heater in a warm garage or basement
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A 50 gallon heat pump tank from a manufacturer with an established residential service channel, which is the part that decides what year eight looks like.
Best for: The standard 50 gallon replacement, done properly
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A hybrid runs its compressor most of the time and falls back to resistance elements on a heavy draw, which is why a hybrid never simply fails to make hot water.
Best for: Households unwilling to risk a slow recovery
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Going up a tank size is the standard fix for a heat pump water heater, because a larger tank lets the slower compressor do more of the work and the elements less.
Best for: Four people who do not want the elements running
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Eighty gallons is tall. Measure the ceiling height and the 700 cubic feet of air a heat pump water heater needs around it before this is on the list at all.
Best for: Large households with the room and the air volume
Check price on AmazonResearched guidance, not professional advice. These results are planning figures from published test procedures, code tables and manufacturer specifications, and they do not replace a sizing done by the person who will sign the permit. A water heater is a pressure vessel: never cap, plug or remove the temperature and pressure relief valve, and replace one that will not open when the test lever is lifted. Gas line, flue and vent work belongs to a licensed plumber or gas fitter, because improper venting produces carbon monoxide. Water at 140 F scalds a child in seconds. Turn off the breaker before touching an element, and never energise an element that is not submerged.
