Natural Gas To Heat Pump Calculator

This calculator weighs keeping your natural gas furnace or boiler against replacing it with an electric heat pump. Enter the gas you use in a year from your bills and the old system's AFUE, or the year it was made; pick the new heat pump from the ENERGY STAR list or enter its HSPF2; and choose any backup heat. It works out the heat your home needs, each system's yearly energy use 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 system, replacing it now, or replacing it when it wears out.

Equipment and climate figures come from federal sources only: ENERGY STAR (EPA), DOE efficiency standards and test procedures, NOAA climate normals and EIA energy prices. You set the installed price; the opening example and each worked example carry a round illustrative price, labelled as such.

Purpose and model boundary

This calculator compares two ways to heat a home: keep the natural gas furnace or boiler you have, or replace it with an electric heat pump. It turns your yearly gas use into the heat your home received, works out the electricity a heat pump needs to deliver the same heat, prices both at your gas and electricity rates, and sets the yearly saving against what the heat pump costs installed. Over the number of years you choose, it compares keeping the old system, replacing it now and, when you say how many years the old system has left, replacing it when it wears out.

Every figure on this page is computed by the spreadsheet; the page adds nothing to it. It covers the running cost of space heating and the purchase cost only. Cooling from the new heat pump is not credited, and a change of distribution system (from a boiler to ducts, or to ductless units) is not modelled.

Inputs and units

• Your gas use: the natural gas you use in a year, in therms, from your bills (0 to 10,000), and the share of it that heats the house. A blank share counts all of it as space heating; if gas also heats your water or cooks, lower the share.
• The old furnace or boiler: its type (furnace, hot-water boiler or steam boiler) and its AFUE, the annual fuel utilization efficiency printed on its nameplate or yellow EnergyGuide label, from 0.40 to 0.99. A steady-state or combustion efficiency is not an AFUE. If the AFUE is unknown, pick the year the system was made and the calculator uses the federal minimum AFUE for that year.
• Optional extras for the old system: the electricity its blower, pump or burner uses in a year, which AFUE leaves out (blank counts none), and the fixed charges you would stop paying by closing the gas account, such as the monthly customer charge.
• The new heat pump: choose its type (ducted split, ductless mini or multi-split, or single package), then the model from that type's ENERGY STAR list, where each entry reads "Brand | Outdoor model"; or enter the HSPF2 from its AHRI certificate. You may also enter your contractor's seasonal COP, from 1.00 to 6.00, which then replaces the rating.
• Backup heat: none beyond the rating, electric resistance, or keeping the existing gas system for the coldest days (dual fuel), with the share of the year's heat the backup supplies, from 0 to 1.
• Prices: the state, which sets the default electricity and gas prices; your own electricity price in dollars per kWh (0.01 to 2.00) and your own gas price in dollars per therm (0.10 to 10.00), each optional.
• Purchase and finance: the installed price of the heat pump, which is always yours to set; extra work such as permits, electrical or duct work; sales tax; verified incentives; removal; the old system's sale value; yearly upkeep of each system; the years the old system has left; the new system's expected life; the yearly change in energy prices; the discount rate; and the years to compare.

Heating and cooling needs are in million Btu (MMBtu) a year of heat delivered or removed. Electricity is in kWh, fuel in US gallons or therms, efficiency ratings in Btu per watt-hour (CEER, SEER2, HSPF2) or as a fraction (AFUE), and money in dollars.

Governing relationships

• Heat delivered by the old system = yearly gas x space-heat share x 100,000 Btu per therm x AFUE.
• Heat-pump electricity = heat needed / (seasonal COP x 3,412 Btu per kWh). The seasonal COP is HSPF2 x 1000 / 3,412 unless you enter your own, so HSPF2 and COP give the same kWh for the same heat.
• Backup heat: HSPF2 already includes the electric resistance heat a heat pump needs in DOE's moderate rating climate (Region IV), so the backup share is extra heat beyond that. Electric backup turns each kWh into 3,412 Btu of heat; dual-fuel backup burns gas at the old system's AFUE.
• Yearly cost = electricity x electricity price + gas x gas price + upkeep, plus, for the old system, the fixed charges the switch avoids. With dual-fuel backup the gas account stays open, so those charges count for the new system too. The yearly saving is the old cost minus the new cost.
• Payback and present value follow the rules shared with the other replacement calculators: a simple payback only when the yearly saving is positive, and the costs of keeping, replacing now and replacing at the end of life discounted over the years you compare, with nothing counted twice.

Calculation sequence

The spreadsheet first checks the inputs and finds the old system's AFUE, the heat pump's rating and the prices. It turns your gas use into the heat your home needed, reduces each system to the energy it uses per million Btu of heat, and from those computes the yearly electricity, gas, costs and saving; the purchase cost, the paybacks, the present values and the year-by-year cash flow follow. The sensitivity tables use the same per-MMBtu figures, so they cannot disagree with the main result. Consistency checks, including that your gas use is reproduced from the computed heat and that the discounted cash flow reaches the same net present value as the closed-form formula, run before the status is returned.

Outputs and interpretation

For each system the results show the heat it delivers, the efficiency used, the yearly electricity and gas, and the yearly energy and total cost; then the yearly saving in dollars, the change in electricity use, the gas saved, the net cost of the heat pump, the simple and discounted payback, and the cost of each path. Switching to a heat pump normally raises electricity use while removing gas use: the change in electricity is shown as old minus new, so it is usually negative, with a sentence that says so. A note states where the heat figure came from: your gas use.

The cash-flow table shows each year of the years compared: the cost of each path, the net benefit of replacing now, and its cumulative, discounted and cumulative discounted values. The first sensitivity table shows the yearly saving with the heat need scaled by 0.50, 0.75, 1.00, 1.25 and 1.50, at the same multiples of the electricity price used. The second sensitivity table shows the yearly saving at 0.50 to 1.50 times the gas price used against 0.50 to 1.50 times the electricity price used. The balance of the two prices is what decides whether switching pays.

A model card beside the heat-pump pick shows the range of its ratings across the indoor units it is certified with, whether ENERGY STAR lists it as cold-climate, and its heating capacity. The calculator uses the lowest SEER2 and HSPF2 among those pairings, so it does not credit a better pairing than the one you may buy.

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 Heating electricity, Gas and fixed gas charges and Auxiliary electricity and upkeep by system, 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: an old-system choice that is not one of its options; no federal minimum AFUE on file for that equipment and year made, in which case use the nameplate AFUE; an AFUE missing or outside 0.40 to 0.99; a heat-pump choice that is not one of its options, a listed model that is not in its list or does not match the type chosen, or a manual HSPF2 missing or outside 5 to 20; a yearly gas use missing or outside 0 to 10,000 therms, or a space-heat share outside 0.05 to 1; a backup choice that is not one of its options, or a backup share outside 0 to 1; a seasonal COP outside 1.00 to 6.00; no electricity price, or your own outside 0.01 to 2.00 dollars per kWh; no gas price at the state, regional or US level and none of your own, or your own outside its limits; a missing installed price, or one outside its limits; a money amount, the years compared, the price change, the discount rate or a life in years outside its limits. 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 AFUE is the federal minimum for the year made; the old system may be more efficient, so the saving may be overstated; a cold state (6,000 heating degree days or more), a heat pump ENERGY STAR does not list as cold-climate, and no backup heat beyond the rating: the HSPF2 rating assumes a moderate climate, so real seasonal efficiency will be lower; with no backup heat, the heat pump's capacity at your coldest month's average temperature is below that month's average heating load, so you may need a larger model, more units or backup heat; the space-heat share is blank, so all the gas is counted as space heating; a yearly gas use of zero; no yearly saving: the heat pump costs as much or more to run, so there is no payback; the old system's remaining life is shorter than the years compared, so read the end-of-life comparison.
• OK otherwise.

Assumptions and limitations

• At US average prices the switch is about even. With the 2025 US average prices, gas burned at an AFUE of 0.80 and a heat pump with an HSPF2 of 9.3 cost almost exactly the same per unit of heat delivered, so the result turns on your own prices and equipment. The opening example is set in Virginia: its heating degree days are almost exactly the US figure, its gas use is the federal survey average for the state, and its prices are the EIA defaults; there the switch saves.
• Your gas year is taken as a typical year. The calculator does not adjust your bills for a mild or a harsh winter.
• Heating only, like for like. Cooling from the new heat pump is not credited; if it also replaces an air conditioner, the cooling side belongs to the heat pump upgrade or central air conditioner calculators. AFUE and HSPF2 both leave out duct and pipe losses, so the comparison is like for like; a change from a boiler to ducts or to ductless units is not modelled.
• A federal minimum is a floor, not a measurement. A system described by the year it was made may be more efficient than the minimum, so the saving may be overstated. Where the minimum changed during a year, the newer, higher minimum is used, which keeps the saving on the low side. Wear with age is not modelled.
• Inputs with no federal source are your assumptions: the installed price, the share of gas used for space heating, any backup share beyond the rating, the old system's auxiliary electricity and the fixed charges avoided. The cold-state threshold of 6,000 heating degree days is a design choice that only sets a warning.
• The size check is lenient by design. A true design load needs a design temperature, and no federal table in this calculator gives one per state. So the check compares the heat pump's capacity at the coldest month's mean temperature, read between its rated capacities at 47 °F and 5 °F, with that month's average heating load, worked out from your own heat use and NOAA's monthly degree-day normals. It warns only when the heat pump cannot meet even that average load and no backup heat is chosen.
• Alaska, Hawaii and DC. NOAA publishes no statewide degree-day normals for any of the three. DC uses Maryland's figures; Alaska and Hawaii each use one NOAA station normal, at the Anchorage and Honolulu airports, labelled as a single station. No figure in this calculator depends on degree days: only the cold-state and size checks read them, and a check is not evaluated where its figures are missing.
• Prices. The installed price of the heat pump is always your input; the workbook holds no price table. The opening example and each worked example carry a round illustrative price so that they compute, with the note: "Illustrative price for this example, not a quote or a current price. Prices vary: check current prices online or enter your own. Get a contractor quote."
• Default energy prices are averages. The state's average residential prices are used unless you enter your own; where EIA publishes no state gas price, the regional or US figure is used and the note says which.

Data and vintage

• Heat pumps: the ENERGY STAR certified air-source heat pump list (EPA), current certifications, one entry per outdoor unit sold in the US, each with the lowest SEER2 and HSPF2 among its certified indoor-unit pairings.
• Federal minimum AFUE by year made: DOE energy conservation standards (10 CFR 430.32), with earlier editions of the Code of Federal Regulations (1997 and 2012) for the years before the current standard.
• Climate: NOAA NCEI statewide heating degree-day normals for 1991-2020 (nClimDiv), with the monthly normals for the size check; the US figure covers the 48 contiguous states. NOAA calls these long-term averages rather than official normals, and its notes state neither the base temperature nor the weighting.
• Default prices: EIA final 2025 average residential electricity prices by state (Form EIA-861), and EIA 2025 average residential natural gas prices by state in dollars per therm, with the regional or US figure where a state has none.
• Heat content: 100,000 Btu per therm and 3,412 Btu per kWh, EIA's sample conversion factors.

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 listed model that is not in its list or does not match the type chosen, a rating or quantity outside its limits, a missing installed price, and a missing electricity or fuel price where no default exists 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 equipment's nameplate or AHRI certificate and your own bills before relying on a result for a purchase, and get a contractor quote for the installed price.

Sources and further reading

The calculator reads its model lists, its federal minimum ratings, its climate figures and its default energy prices from reviewed reference tables inside the workbook, 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 data portal catalog (EPA) lists the EPA's certified-product datasets, among them the heat pump list used here (retrieved 2026-10-28).
• ENERGY STAR Certified Heat Pumps (EPA) lists certified air-source heat pumps by outdoor and indoor unit, with SEER2, HSPF2, heating capacity at 47 °F and 5 °F, and a cold-climate flag (retrieved 2026-10-28).
• ENERGY STAR air-source heat pumps: information for partners (EPA) links the ENERGY STAR heat pump specification, whose criteria include the cold-climate designation shown on the model card (retrieved 2026-10-28).
• DOE energy conservation standards, 10 CFR 430.32 (eCFR) sets the federal minimum AFUE for furnaces and boilers and the minimum ratings for heat pumps; earlier editions give the older levels (retrieved 2026-10-28).
• DOE test procedures, 10 CFR 430 subpart B (eCFR) defines HSPF2 for heat pumps and AFUE for furnaces and boilers (retrieved 2026-10-28).
• NOAA NCEI, Climate Divisional Database (nClimDiv) publishes statewide degree-day normals, used here for 1991-2020 (retrieved 2026-10-28).
• NOAA NCEI, U.S. Climate Normals 1991-2020, station files gives the Anchorage and Honolulu airport normals that stand in for Alaska and Hawaii (retrieved 2026-10-28).
• EIA, British thermal units (Btu) gives 100,000 Btu per therm and 3,412 Btu per kWh (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 average residential natural gas price by state, used here for 2025 (retrieved 2026-10-28).
• EIA, Residential Energy Consumption Survey 2020, state data gives typical space-heating gas use per household by state for 2020, a cross-check for your own figure (it is not a value in the calculator, apart from setting the opening example's gas use) (retrieved 2026-10-28).

This is an educational estimate of running and purchase costs for the equipment and prices you enter, not a product recommendation or a quote. Ratings are measured under federal test procedures, not in your home.