Calculators
Heating and cooling cost calculators
What a system costs to run, fuels compared per million BTU, thermostat setbacks, degree days, filters, upgrade paybacks and duct leakage.
Running cost is energy multiplied by price, and the energy is the house's heat load multiplied by hours and divided by the equipment efficiency. Every calculator in this group is a version of that sentence with the right efficiency rating in the denominator: SEER2 for cooling, AFUE for a furnace, HSPF2 or COP for a heat pump, UEF for a water heater. Prices default to the US Energy Information Administration's residential averages and are meant to be replaced with the figures on your bill.
The interesting questions are comparisons: a heat pump against a gas furnace at your prices, a setback against a constant thermostat, a 16 SEER2 unit against the 14 SEER2 one that costs less, sealing the ducts against leaving them. Each comparison calculator shows both sides and the break-even, so the decision can be made on numbers that are yours.
8 calculators
HVAC Running Cost Calculator
Cost per hour, day and month for an air conditioner, furnace, heat pump or electric heat from its output and rating.
Heat Pump vs Gas Furnace Cost Calculator
A season of heating with a heat pump against a gas, propane or oil furnace, with backup heat and the break-even price.
Thermostat Setback Savings Calculator
What lowering the thermostat at night or while out saves a season, with the heat pump caveat and the thermostat payback.
Degree Days Fuel Estimate
A season of heating fuel from the design heat loss and heating degree days, with the fuel per degree day to check bills.
Fuel Cost per Million BTU Calculator
Gas, propane, oil, electricity, heat pump, pellets and wood ranked by the cost of a million BTU of heat delivered.
HVAC Filter Cost Calculator
How often to change the furnace filter for its thickness, pets and allergies, and what a year of filters costs.
HVAC Upgrade Payback Calculator
Annual saving, payback and net gain of a more efficient furnace, boiler, AC, heat pump or water heater, after rebates.
Duct Leakage Loss Calculator
What leaky ducts in an attic, crawl space or basement cost a year, and the payback of sealing them.
Guides for this topic
Comparing gas, propane, oil, electric and heat pumps per million BTU
Therms, gallons, kWh and tons do not compare directly. Turn each into dollars per million BTU of heat delivered and the cheapest fuel is obvious.
Heating and cooling degree days explained
Degree days measure how cold or hot a season was in a single number. Multiply by the house's heat loss per degree and you have the season's heating energy.
Duct leakage: the 20% you pay for and never feel
Ducts in an attic or crawl space typically leak a fifth or more of the air the system makes. Sealing them is one of the best paybacks in a house.
Heat pumps in cold climates: balance point and backup heat
A heat pump sized for summer can heat most of a northern winter. The question is what happens below the balance point, and the answer is a few lines of arithmetic.
MERV filters: filtration vs airflow, and the replacement schedule
A better filter catches more and restricts more. The answer is rarely the cheapest or the highest MERV; it is the right rating in a filter deep enough for the system.
SEER2, HSPF2, AFUE and COP: the ratings explained
Every efficiency rating is output divided by input. Once you know what each one counts, comparing equipment and estimating what it costs to run is simple arithmetic.
Thermostat setbacks: how much they save, and when they don't
Turning the heat down for eight hours saves about one percent of the bill per degree. The rule is simple; the exceptions are where people lose the saving.
What a water heater costs to run, by fuel and type
Water heating is often the second-largest energy bill in a house. Three numbers, gallons a day, the temperature rise and the UEF, give its cost.
Questions people ask
- How much does central air conditioning cost per month?
- A 3-ton system at 15 SEER2 draws about 2.4 kW while running. At 8 hours a day for 30 days that is 576 kWh, or about $98 at the US average of 17 cents per kWh. Hot climates and leaky houses double the hours; a 10 SEER unit from the 1990s uses half again as much electricity for the same cooling. The AC running cost calculator uses your tonnage, rating, hours and price.
- Is a heat pump cheaper to run than a gas furnace?
- At US average prices, usually yes in mild and moderate climates and roughly even in cold ones. A heat pump at a seasonal COP of 2.8 delivers a million BTU for about $18 at 17 cents per kWh; a 95% gas furnace at $1.50 per therm delivers the same for about $16. The break-even is a ratio. With a 95% furnace, a heat pump wins when the electricity price in cents per kWh is below about 3.6 times the gas price in dollars per therm times the COP, which at $1.50 gas and a COP of 2.8 is about 15 cents. Backup strip heat in cold weather lowers the effective COP; the comparison calculator includes it.
- How much does a thermostat setback save?
- The US Department of Energy puts the saving at about 1% of the heating bill for each degree Fahrenheit of setback held for 8 hours, so a 7 °F overnight setback saves about 7%, and a setback for both night and the working day saves up to 10%. The saving is smaller for heat pumps with resistance backup, which can run the backup strips when recovering from a deep setback, and the calculator says so.
- What are heating degree days and how do I use them?
- A heating degree day is one degree of average outdoor temperature below 65 °F for one day. Chicago has about 6,300 a year; Atlanta about 2,700; Miami about 130. Multiply your house's heat loss per degree by 24 hours and by the degree days to get the season's heat demand in BTU, then divide by the furnace efficiency and the fuel's energy content to get gallons, therms or kWh. The degree-day calculator carries a regional table.
- How often should I change my HVAC filter?
- A standard 1-inch pleated filter every 90 days, every 60 days with a pet or a dusty site, and every 30 to 45 days with several pets or allergies in the household. Thicker 4 to 5 inch media filters last 6 to 12 months. The filter cost calculator turns your filter price and interval into an annual budget and a replacement schedule.
More calculators on our other sites
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