Electric To Heat Pump Water Heater Calculator

This calculator weighs keeping an electric resistance water heater against replacing it with a heat-pump water heater. Describe the old tank by the electricity it uses a year, by the year it was made and its size, or from its efficiency rating or EnergyGuide label. Then pick the heat pump from the ENERGY STAR list and enter what you pay for electricity and what the switch costs installed, including any electrical work. It works out each heater's yearly electricity and cost, the yearly saving, the net cost of the heat pump, the simple and discounted payback, and the cost over the years you choose of keeping the old tank, replacing it now, or replacing it when it wears out.

Model figures come from federal sources only: the ENERGY STAR certified list published by the EPA, and the DOE test procedure and efficiency standards. Default electricity prices come from the EIA. You set the price of the heat pump; the opening example carries an illustrative one.

Purpose and model boundary

This calculator compares keeping an electric resistance water heater with replacing it with a heat-pump water heater. It works out the heat your household's hot water needs each year, either from your hot water use or from the electricity your old tank uses now, divides it by each heater's DOE efficiency rating to get the electricity each uses, prices that at your electricity rate, and sets the yearly saving against what the heat pump costs installed. Over the years you choose, it compares keeping the old tank, replacing it now and, when you say how many years the old tank has left, replacing it when it wears out.

Every figure on this page is computed by the spreadsheet; the page adds nothing to it. The model covers running cost and purchase cost only, for electricity alone. It does not judge recovery speed, hot-water capacity at peak use, noise or reliability, and it does not price financing, warranties or your own time.

Inputs and units

• The old electric tank, described in one of three ways:
  • the electricity it uses a year for hot water, from your bills or a meter (the default), with its efficiency if you know it; blank uses the current federal minimum for a 50-gallon tank;
  • the year it was made and its tank size in gallons: the calculator then uses the federal minimum efficiency for that year;
  • manual entry: its UEF, its EF from the older DOE test, or the yearly electricity on its EnergyGuide label with the label's draw pattern (Very small, Low, Medium, High, the older label's 64.3 gallons a day, or Unknown, where it starts).
• The new heat-pump water heater: a model from the current ENERGY STAR list of heat-pump water heaters, or its UEF by hand, and its price, more than $0 and at most $20,000. Each entry reads "Brand | Model number", exactly as ENERGY STAR lists it.
• Hot water use: gallons a day, 0 to 200, read when the old tank is described by its year made or its rating (the default is 55, the DOE's medium draw pattern); optionally your setpoint (blank uses the DOE's 125 °F) and the temperature of the incoming cold water (blank uses 58 °F). With the yearly-use route the calculator works out your hot water use from your electricity instead.
• Electricity price, optional: the state sets the default; your own price in dollars per kWh overrides it.
• Purchase and upkeep: installation, electrical work (often a new circuit), permit, removal and disposal of the old tank, sales tax on the price, verified rebates and tax credits, and yearly upkeep for each. Each is optional and counts as zero when left blank.
• The comparison: the years to compare (1 to 30), the yearly change in the electricity price, the discount rate, and, optionally, the years the old tank has left and the expected life of the heat pump.

Energy is in kWh, hot water in US gallons a day, temperatures in °F and money in dollars. A water heater's rating, the uniform energy factor (UEF), is the heat delivered in hot water per unit of electricity used: higher is better.

Governing relationships

Heat needed. The yearly heat in your hot water is gallons a day × 365 × 8.24 pounds per gallon × 1 Btu per pound per °F × the temperature rise, the setpoint less the inlet temperature (67 °F at the DOE's 125 °F and 58 °F).

Electricity used. Each heater's yearly electricity is that heat ÷ its UEF ÷ 3,412.14 Btu per kWh. Heat-pump water heaters on the current list are rated from 2.52 to 4.5; a resistance tank turns each kWh into less than one kWh of hot water, so at the same hot water use a heat pump always uses less electricity.

Starting from your yearly electricity. When you enter the electricity your old tank uses a year, the calculator works out the heat it delivers, that use × 3,412.14 Btu per kWh × the old tank's UEF, and the heat pump's electricity is your use × the old UEF ÷ the new UEF. Your hot water use is then implied, and shown so that you can check it against the DOE's patterns; outside 10 to 120 gallons a day, the status says so. Left blank, the old tank's UEF is the current federal minimum for a 50-gallon electric tank, 0.9207, and a note says so.

What the rating includes. A UEF already includes a tank's standby losses, so they are not added again; the calculator scales them with your hot water use, which is the method's limit.

Older ratings and labels. A tank rated by EF, the DOE's older test (135 °F outlet), is used as if its EF were a UEF, without conversion, and the status says so. A yearly figure from an EnergyGuide label is scaled to your use: the label assumes the DOE draw pattern it names, or 64.3 gallons a day at a 77 °F rise for an older label; with the pattern unknown, the label figure is used as it stands.

A tank described by the year it was made. No DOE figures for typical tanks by year were available, so the calculator uses the federal minimum efficiency for that year and tank size: your tank may be more efficient, so the saving may be overstated, and the status says so.

• The minimum falls with tank size: 0.95 − 0.00132 × the volume for an electric tank made from 1990, 0.93 − 0.00132 × V from April 15, 1991, 0.97 − 0.00132 × V from 2004; from April 16, 2015 it depends on whether the tank holds more than 55 gallons. The calculator uses those 2015 limits for every tank made since, as the UEF: DOE's later UEF table restates the same standards.
• Above 55 gallons, an electric tank made after April 16, 2015 must meet a heat-pump level of efficiency, so a large resistance tank of that age is unusual.

Yearly cost. For each heater, the yearly utility cost is its kWh times the electricity price. Adding yearly upkeep gives its yearly cost, and the yearly saving is the old tank's yearly cost less the heat pump's.

Purchase cost. The capital cost is the price × (1 + sales tax rate) + installation + electrical work + permit − rebates and credits. The net initial cost adds removal and disposal; a used tank has no resale value.

Payback. Simple payback is the net initial cost ÷ the first year's saving, when the saving is positive; otherwise there is no payback. Discounted payback is the first year in which the cumulative discounted net benefit of replacing now reaches zero within the years compared.

The three paths over the years compared. The electricity price changes each year by the rate you enter; upkeep stays flat; costs fall at the end of each year and are discounted at your rate.

• Keep: the old tank's yearly cost every year.
• Replace now: the net initial cost today, then the heat pump's yearly cost, less the value left in it at the end.
• Replace at end of life (when you enter the years the old tank has left and they are fewer than the years compared): the old tank's yearly cost until it fails, then the capital cost and disposal in that year at today's price, then the heat pump's yearly cost, less the value left in it at the end.

The value left in the heat pump at the end is its capital cost × the share of its expected life still remaining, on a straight line. Enter its expected life, or leave it blank to use the DOE's typical lifetime for a water heater, 15 years. The net present value of replacing now is the present cost of keeping less the present cost of replacing now: positive means replacing now costs less.

Calculation sequence

The spreadsheet first finds the old tank's yearly use or rating and the heat pump's rating from the list, the year table or your entries, and checks the inputs. It then works out the yearly heat your hot water needs, divides it by each heater's rating to get its electricity, and from that computes the yearly costs and the saving. The purchase cost, the paybacks, the present values of the three paths and the year-by-year cash flow follow. The sensitivity table uses the same per-gallon figures, so it cannot disagree with the main result. A block of consistency checks, including that the discounted cash flow reaches the same net present value as the closed-form formula, runs before the status is returned.

Outputs and interpretation

The headline is the yearly saving from replacing the old tank, with the simple payback and the net present value of replacing now. For each heater the results give its yearly kWh and its yearly energy and total cost, with the electricity price actually used and a note on where it came from; on the yearly-use route, the hot water use your figures imply. The decision results give the net initial cost, the discounted payback year, the total and present cost of keeping, of replacing now and of replacing at end of life, and a plain verdict on each.

The cash-flow table shows each year from 0 to the years compared: the cost of each path, the net benefit of replacing now, and its cumulative, discounted and cumulative discounted values. The sensitivity table shows the yearly saving at 10, 20, 38, 55, 70, 84, 100 and 120 gallons of hot water a day, and at 0.50 to 1.50 times the electricity price used.

A model card beside the heat-pump pick shows its type (240 V or 120 V integrated, or split), tank size, draw pattern, first-hour rating, UEF and the year it became available.

The first chart, “Cumulative net benefit of replacing now, by year”, shows Undiscounted and Discounted by year. The second chart, “Cost over the years compared”, shows Total and Present value by option. The third chart, “Running cost in year 1”, shows Energy and Upkeep by unit, stacked.

Validation and status logic

The workbook returns one status, chosen in this order: NOT VALID, then CHECK, then OK.

• NOT VALID names the first problem: a source that is not one of its options; a heat-pump model that is not in the list; no year made, or no federal limit for that year and volume; a yearly use missing or not above 0 and at most 15,000 kWh, a UEF or EF outside 0.40 to 5.00, or a label figure not above 0 and at most 10,000 kWh; a label draw pattern that is not one of its options; a tank size missing or outside 20 to 120 gallons; an upkeep figure outside its range; hot water a day outside 0 to 200 gallons when it is read, or a setpoint or inlet temperature out of range; no electricity price, or your own price outside $0.01 to $2.00 per kWh; a price for the heat pump that is missing, not above $0 or above $20,000; another money or rate input outside its range; or years to compare, years left or expected life that are not whole numbers in range. NOT VALID is a refusal, not a numeric answer: every figure reads zero and is withheld.
• CHECK accompanies a computed result that needs the stated review: the federal minimum efficiency used for a tank described by its year made, so it may be more efficient and the saving may be overstated; an old tank rated by EF, the older DOE test, used without conversion; a label figure whose draw pattern is unknown, so it is used without scaling to your hot water use; a yearly use that implies hot water outside 10 to 120 gallons a day; zero hot water a day; a heat pump that does not cost less to run than the old tank, so there is no payback; or an old tank with fewer years left than the years compared, so the end-of-life path is the realistic one.
• OK otherwise.

Assumptions and limitations

• There is no list of electric resistance tanks. ENERGY STAR does not certify them, so the old tank is described by its yearly electricity, its year made or its own rating.
• The federal minimum is a floor, not a measurement. A tank described by its year made, or whose efficiency is left blank on the yearly-use route, may be more efficient, so the saving may be overstated.
• Your yearly electricity must be for hot water only. A figure from your bills that includes other uses overstates the saving; check the hot water use it implies.
• Heat pumps in cold spaces are not modelled. A heat-pump water heater is rated at 67.5 °F; in a cold or unconditioned space its compressor does less and its backup elements more, and it cools the room it stands in. The calculator uses the rating as it stands.
• The default electricity price is an average: the EIA's annual average residential price for the state, not your tariff. Enter your own price from your bill for a better answer.
• The future purchase in the end-of-life path is priced at today's price. There is no loan and no depreciation other than the value left in the heat pump at the end.

Data and vintage

The heat-pump list, the year table and the default electricity prices are reviewed reference tables inside the workbook, refreshed from their federal publishers; their version is shown in the result details.

• Heat-pump models: the heat-pump water heaters in the ENERGY STAR certified water heaters dataset (EPA), 717 rows of which 613 are for the US market, downloaded 2026-10-28.
• Year made: the federal minimum efficiency for electric water heaters by date of manufacture and tank size, 10 CFR 430.32(d), from the 1990 standard on.
• Default electricity prices: EIA 2025 annual average residential electricity prices by state (Form EIA-861).

Worked examples and prices

Prices are not part of the reference data: the price of the new unit is an input you set. The opening example and the five worked examples each use an illustrative price for the new unit, so that the example computes, and each says so: “Illustrative price for this example, not a quote or a current price. Prices vary: check current prices online or enter your own.”

Restrictions and non-computing states

The calculator enforces its numeric and choice limits before it accepts a result. A heat-pump model that is not in the list, an old tank with no yearly use, year or rating, and a missing price for the heat pump are refused by the workbook.

Errors and warnings

A request rejected by the page's input limits is not a computed result. A transport or service failure, a timeout or a cancelled run cannot establish a fresh workbook answer, and the last result stays on the page marked as out of date. Check your unit's label or specification sheet and your own bills before relying on a result for a purchase.

Sources and further reading

The calculator reads its model lists, its year-made limits and its default utility prices from reviewed reference tables inside the workbook, by record, with their version shown in the result details. Every table comes from a US federal source. The sources below publish the data and the rules the model applies. They do not endorse this calculator.

• ENERGY STAR Certified Water Heaters (EPA) lists currently certified water heaters, including heat-pump models with their tank size, draw pattern, UEF and yearly electricity at the DOE's 125 °F test outlet (retrieved 2026-10-28).
• DOE energy conservation standards, 10 CFR 430.32 (eCFR), paragraph (d), sets the federal minimum efficiency for water heaters by date of manufacture and tank size; earlier editions on govinfo hold the older limits (retrieved 2026-10-28).
• EIA, Detailed state data (Form EIA-861) gives the average residential electricity price by state, used here for 2025 (retrieved 2026-10-28).
• DOE water-heater energy conservation rule provides the water-heater lifetime basis used for the new unit's remaining value.
• DOE water-heater test procedure, Appendix E (govinfo) defines the water-heater test procedure and Uniform Energy Factor.
• DOE water-heater conversion-factors final rule supplies the conversion equations from older Energy Factor ratings to Uniform Energy Factor.

This is an educational estimate of running and purchase costs for the units and prices you enter, not a product recommendation or a quote. The ENERGY STAR lists show each model's rated use under the DOE test procedure, not your unit's measured use; check your own bills before acting on a result.