Furnace Sizing Calculator
Estimate your home's heating load and the approximate furnace input needed at a selected efficiency.
Quick Estimate
A rough estimate using the factor you enter. This factor is a user-selected assumption, not an official climate-zone standard.
The default factor is illustrative only. Change it to a value appropriate for your own preliminary estimate; the calculator does not infer a factor from climate or insulation.
Heating Load
Enter the total heating load from a suitable heat-loss calculation. If using Homecostify Heating BTU Calculator, copy its total heating load here; this is not an automatic plugin connection.
Use the AFUE shown for the furnace you are evaluating. AFUE is not a substitute for the manufacturer's capacity and performance data.
Estimated heating load
— kW
These figures are estimates, not a recommendation for a specific furnace model. Check the manufacturer's rated heating output at the relevant operating conditions and have equipment selected using an appropriate load calculation and sizing procedure.
How to Use the Calculator
- Choose Heat-Loss Based if you already know the home's heating load, or Quick Estimate for a rough area-based estimate.
- Choose US or Metric units. In Quick Estimate, the heating factor unit changes with your selected measurement system.
- For Heat-Loss Based, enter the total heating load manually or copy the total from Homecostify Heating BTU Calculator.
- Select the furnace's AFUE from its product information.
- Results update automatically as you enter or change valid inputs.
Assumptions and Limitations
- Quick Estimate multiplies heated floor area by the user-selected BTU/h-per-ft² factor. The default factor is illustrative and is not a validated climate-zone recommendation.
- Heat-Loss Based assumes the entered load is a suitable estimate of the building's design heating load.
- Required output capacity is approximated as equal to the entered heating load. Estimated input is heating load divided by AFUE as a decimal.
- This tool does not calculate an ACCA Manual J load, account automatically for climate, insulation, ducts, or infiltration, or select a specific furnace model.
- Actual furnace selection should account for manufacturer performance data and an appropriate equipment-sizing method, such as ACCA Manual S where applicable.
