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HVAC made simple
HVAC CALCULATOR
Gas Furnace Cost Calculator
Estimate how much it may cost to run your natural gas furnace based on furnace capacity, AFUE efficiency, local gas price, and estimated heating runtime.
1. Gas Furnace Details
Enter the input capacity and efficiency rating of your furnace.
BTU/hr
Use the furnace input rating, not the output rating.
This can usually be found on the furnace data plate
or manufacturer specifications.
%
Common ratings include approximately 80%, 90%, 95%,
96%, and 98% AFUE.
Common furnace sizes:
2. Natural Gas Price
Enter your approximate delivered natural gas price.
$
per therm
Check your utility bill for your actual gas rate.
One therm represents approximately 100,000 BTUs
of fuel energy.
What is a therm?
1 therm ≈ 100,000 BTU
Natural gas utilities commonly bill residential customers using therms or another energy-volume unit.
3. Furnace Runtime
Estimate the furnace’s actual burner runtime during a typical heating day.
hours
Enter cumulative burner runtime rather than the number
of hours the thermostat is switched on.
days
Heating-season length varies considerably by climate
and weather.
Not sure about furnace runtime?
Furnace runtime changes with outdoor temperature, thermostat
setting, insulation, air leakage, equipment sizing, furnace
staging, and home construction. Try several runtime estimates
to see a range of possible operating costs.
4. Blower Electricity (Optional)
A gas furnace also uses electricity to operate its blower and controls.
YOUR ESTIMATE
Estimated Gas Furnace Operating Cost
Based on the furnace capacity, gas price, and runtime you entered.
Estimated Heating Season Cost
$0
Natural gas operating estimate
Cost per Hour
$0.00
Cost per Day
$0.00
Estimated 30-Day Cost
$0.00
Heating Season Cost
$0.00
Your Furnace Cost Breakdown
Furnace Input Capacity
—
Furnace AFUE
—
Approximate Useful Heat Output
—
Gas Used per Operating Hour
—
Gas Used per Heating Day
—
Estimated Seasonal Gas Use
—
Gas Price Used
—
Estimated Seasonal Runtime
—
Where Does the Fuel Energy Go?
💡 How This Calculation Works
Gas Furnace Cost Formula
Therms per operating hour
Furnace Input BTU ÷ 100,000
Fuel cost per hour
Therms per hour × Gas price per therm
Useful heating output
Input BTU × AFUE
Seasonal cost
Hourly cost × Runtime/day × Heating days
🔥 Input BTU vs. Output BTU
Natural gas consumption should be estimated from the furnace’s input capacity. AFUE helps estimate how much of that fuel energy becomes useful heat. For example, an 80,000 BTU/hr input furnace at 95% AFUE has an approximate useful output of 76,000 BTU/hr.
Important:
This calculator provides an educational estimate of gas
furnace operating costs. Actual consumption and utility
bills can vary substantially based on outdoor weather,
furnace staging or modulation, cycling, thermostat settings,
home heat loss, ductwork, equipment condition, altitude,
gas heating value, utility rate structure, taxes, fees,
blower operation, and household behavior. AFUE is a seasonal
efficiency metric and should not be interpreted as an exact
steady-state efficiency under every operating condition.
Check your furnace specifications and current utility rates
when evaluating actual operating costs.