Household Heating Tool
Gas Furnace Operating Cost Calculator
Calculate residential gas furnace heating costs by input capacity (Btu/hr) or heating output rating with AFUE efficiency percentage, runtime hours, and therm gas pricing.
100,000 Btu/hr
150.0 therms
$9.57 / day
$287.12
- Furnace heating output rated at 80,000 Btu/hr with 80% AFUE seasonal efficiency (input capacity: 100,000 Btu/hr).
- Burner runtime estimated at 5 hours per day over 30 active heating days (150 total runtime hours).
- Natural gas pricing assumed at $1.91 per therm (1 therm = 100,000 Btu).
- Calculates volumetric natural gas usage cost only. Electricity needed for the furnace blower motor (typically 300W to 800W) is not included.
- Thermostat cycling, outdoor winter temperatures, building insulation, and duct losses alter actual burner firing hours.
- Utility fixed monthly customer charges, delivery fees, and taxes are excluded.
How Furnace Gas Consumption Is Calculated
Furnace heating expenses depend on burner input capacity (BTU/hr), annual fuel utilization efficiency (AFUE), and burner runtime duration:
Therms per Hour = Input Capacity (BTU/hr) ÷ 100,000 BTU/ThermOperating Cost ($) = (Therms/Hour × Daily Runtime Hours × Days) × Rate per Therm ($)Frequently Asked Questions About Gas Furnace Costs
How do I calculate how much natural gas my furnace uses per hour?
Divide your furnace input rating in BTU/hr by 100,000 to find Therms consumed per full burner hour. For example, an 80,000 BTU/hr furnace burns 0.80 Therms per active hour ($1.53/hr at $1.91/therm national average gas price).
What is the difference between an 80% AFUE and 96% AFUE gas furnace?
AFUE (Annual Fuel Utilization Efficiency) measures combustion efficiency. An 80% standard furnace vents 20% of heat out the chimney, whereas a 96% high-efficiency condensing furnace captures almost all waste heat, saving 16% to 20% on annual winter heating bills.
How many hours a day does a gas furnace run in winter?
Under typical winter weather (30°F–40°F), a properly sized residential furnace runs 5 to 8 hours total per day (cycling on and off). During extreme sub-zero cold snaps, runtimes can reach 12 to 16 hours daily.
Is natural gas heating cheaper than electric resistance heat?
Yes. Natural gas delivered at $1.91 per therm provides 100,000 BTU of heat for $1.91. Delivering that same 100,000 BTU with electric resistance baseboards or space heaters (29.3 kWh at 18.4¢/kWh) costs $5.39—making natural gas nearly 65% cheaper per unit of thermal heat.