Water Heater Replacement Calculator

This calculator weighs keeping your water heater against replacing it, including a switch of fuel or type, such as from a gas or electric tank to a heat pump or a tankless heater. Describe the old heater by picking its model from the ENERGY STAR lists, by the year it was made and its tank size, or from its efficiency rating or EnergyGuide label. Then pick the new model, say how much hot water you use a day, and enter what you pay for electricity, natural gas or propane. It works out each heater's yearly energy use and cost, the yearly saving, the net cost of the new heater installed, the simple and discounted payback, and the cost over the years you choose of keeping the old heater, replacing it now, or replacing it when it wears out.

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

Purpose and model boundary

This calculator compares two ways forward for a household water heater: keep the one you have, or replace it with a new one, including a switch of fuel or type, such as from a gas tank to a heat-pump water heater. It works out the heat your household's hot water needs each year, divides it by each heater's DOE efficiency rating to get the energy each uses, prices that at your electricity, natural gas or propane rate, and sets the yearly saving against what the new heater costs installed. Over the years you choose, it compares keeping the old heater, replacing it now and, when you say how many years the old one 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. 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 water heater, described in one of four ways:
  • a model from the ENERGY STAR historical lists, for a heater rated by UEF that is no longer on the current list; each entry names its fuel, "Brand | Model (Natural gas)";
  • a model from the current ENERGY STAR list, for a heater that is still certified;
  • the year it was made and its tank size in gallons, when the model is not listed: 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 energy 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).
• Type: Heat pump, Gas storage or Gas tankless for either heater, and Electric storage (resistance) for the old one. ENERGY STAR has never certified resistance tanks, so an old one is described by its year made or by hand. For a listed model, choose the type first, then pick the model from that type's list; each entry reads "Brand | Model number", exactly as ENERGY STAR lists it.
• Gas fuel: for a gas heater, natural gas or propane. Gas water heaters are listed per fuel, so the model you pick must be listed for the fuel you choose.
• The new water heater: a model from the current ENERGY STAR list, or its UEF by hand, and its price, more than $0 and at most $20,000.
• Hot water use: gallons a day, 0 to 200; the default is 55, the DOE's medium draw pattern (the others are 10, 38 and 84 gallons a day). Optionally, your water heater's setpoint (100 to 160 °F; blank uses the DOE's 125 °F) and the temperature of the incoming cold water (35 to 80 °F; blank uses 58 °F).
• Utility prices, each optional: the state, which sets the default electricity price; your own electricity price in dollars per kWh; your own natural gas price in dollars per therm or propane price in dollars per gallon (shown when a heater uses that fuel). A blank price uses the default described under "Data and vintage".
• Purchase and upkeep: installation, electrical work (for example a new circuit for a heat pump), permit, removal and disposal of the old heater, 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 utility prices, the discount rate, and, optionally, the years the old heater has left and the expected life of the new one.

Energy is in kWh, natural gas in therms, propane in US gallons, 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 energy 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).

Energy used. Each heater's yearly energy is that heat ÷ its UEF, in kWh at 3,412.14 Btu per kWh for an electric or heat-pump heater, in therms at 100,000 Btu for natural gas, and in gallons for propane. This is the same rule ENERGY STAR's own yearly figures follow: for example, a gas storage heater with a UEF of 0.90 at the DOE's high draw of 84 gallons a day uses 84 × 365 × 8.24 × 67 ÷ 0.90 ÷ 100,000 = 188 therms a year.

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. A gas heater's UEF also includes its small electricity use (fan, controls), which the calculator prices as gas.

Older ratings and labels. A heat-pump water heater rated by EF, the DOE's older test (135 °F outlet), is converted to a UEF with DOE's published conversion; any other heater's EF, and the federal limits by year made, are used as if the 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 heater described by the year it was made. No DOE figures for typical heaters by year were available, so the calculator uses the federal minimum efficiency for that year, fuel and tank size: your heater may be more efficient, so the saving may be overstated, and the status says so.

• The minimum falls with tank size. From 1990 it was 0.62 − 0.0019 × the volume for gas and 0.95 − 0.00132 × the volume for electric tanks; from 2004, 0.67 − 0.0019 × V for gas and 0.97 − 0.00132 × V for electric; from April 16, 2015 it depends on whether the tank holds more than 55 gallons. The calculator uses those 2015 limits for every heater 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, plus its therms times the gas price or its propane gallons times the propane price. Adding yearly upkeep gives its yearly cost, and the yearly saving is the old heater's yearly cost less the new one'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 water heater 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. Utility prices change 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 heater's yearly cost every year.
• Replace now: the net initial cost today, then the new heater's yearly cost, less the value left in it at the end.
• Replace at end of life (when you enter the years the old heater has left and they are fewer than the years compared): the old heater's yearly cost until it fails, then the capital cost and disposal in that year at today's price, then the new heater's yearly cost, less the value left in it at the end.

The value left in the new heater 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 each heater's type, fuel and 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 energy in its own fuel, 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 heater, with the simple payback and the net present value of replacing now. For each heater the results give its yearly kWh, therms or propane gallons, and its yearly energy and total cost, with the prices actually used and a note on where each came from. 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 price of the fuel that makes up most of the old heater's running cost; its note names that fuel.

A model card beside each pick shows the model's type, fuel, tank size, draw pattern, first-hour rating, rating and the year it was listed or 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, or a list chosen for an electric resistance tank; a listed model that is not in its list or whose type differs from the type chosen; no year made, or no federal limit for that type, fuel, year and volume; a manual rating that is not one of its kinds, or a value out of range (a UEF or EF of 0.40 to 5.00; a label figure above 0 and at most 10,000 kWh, 600 therms or 700 gallons); a label draw pattern that is not one of its options, or the older-label basis chosen to convert a heat pump's EF, which needs a DOE draw pattern; a tank size missing or outside 20 to 120 gallons; a gas heater whose fuel is not natural gas or propane, or a model not listed for that fuel; an upkeep figure outside its range; hot water a day outside 0 to 200 gallons, or a setpoint or inlet temperature out of range; no electricity price, or your own price outside $0.01 to $2.00 per kWh; no price for a fuel in use, or your own gas price outside $0.10 to $10.00 per therm or propane price outside $0.50 to $10.00 per gallon; a price for the new heater 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 heater described by its year made, so it may be more efficient and the saving may be overstated; an old heater 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 fuel price that is a regional or US average, because EIA publishes none for your state; zero hot water a day; a new heater that does not cost less to run than the old one at your use and prices, so there is no payback; or an old heater with fewer years left than the years compared, so the end-of-life path is the realistic one.
• OK otherwise.

Assumptions and limitations

• The historical lists hold only ENERGY STAR heaters rated by UEF: no standard gas tanks and no electric resistance tanks, which are the usual old heaters, and no heater rated only by the older EF test. A listed model that stands in for a different heater probably used less than a typical one of its age, so the saving may be understated; a standard tank is better described by the year it was made.
• The federal minimum is a floor, not a measurement. A heater described by its year made may be more efficient, so the saving may be overstated.
• The DOE draw patterns are the rating's basis, not your use. Your use enters through gallons a day and your temperatures; actual use depends on your household's draws and inlet temperature.
• 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.
• Default utility prices are averages. The default electricity price is the EIA's annual average residential price for the state, not your tariff; the gas and propane prices are EIA residential averages for the state, or a regional or US average where EIA publishes none. Enter your own prices from your bills for a better answer.
• One price change rate applies to every utility price alike. 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 new heater at the end.

Data and vintage

The model lists, the year table and the default prices are reviewed reference tables inside the workbook, refreshed from their federal publishers; their version is shown in the result details.

• Current models: the ENERGY STAR certified water heaters dataset (EPA), 1,374 rows, downloaded 2026-10-28: heat-pump, gas storage and gas tankless heaters for the US market; solar heaters, rated by a different measure, are left out.
• Historical models: the ENERGY STAR historical lists (specification versions 3 and 4, heaters certified from 2012 to 2023), keeping only heaters rated by UEF, the most recent listing of each model, and none still on the current list; implausible values are set aside.
• Year made: the federal minimum efficiency for water heaters by date of manufacture, fuel and tank size, 10 CFR 430.32(d), from the 1990 standard on.
• Default utility prices: EIA 2025 annual average residential electricity prices by state (Form EIA-861); EIA 2025 residential natural gas prices by state, converted to dollars per therm with each state's heat content (for the US, $15.34 per thousand cubic feet, or $1.4807 per therm); and EIA residential propane prices.

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 model that is not in its list, does not match the type chosen or is not listed for the fuel chosen, a list chosen for an electric resistance tank, a manual heater with no rating and a missing price for the new heater 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 heat-pump, gas and solar water heaters with their type, fuel, tank size, draw pattern, UEF and yearly energy use at the DOE's 125 °F test outlet (retrieved 2026-10-28).
• ENERGY STAR, Residential water heaters: information for partners (EPA) links the historical lists of water heaters certified under earlier specifications, versions 1.1, 2, 3 and 4 (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, fuel 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).
• EIA, Natural gas prices gives the residential price by state, used here for 2025, and EIA, Heat content of natural gas delivered to consumers the heat content used to convert it to dollars per therm (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.
• EIA Energy Explained: units and calculators provides the energy-unit conversion basis.
• EIA residential heating oil and propane prices publishes residential propane prices; defaults use a heating-season average, with a regional or national fallback where a state figure is unavailable (retrieved 2026-10-28).

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.