Formula and input notes
Screening heating load (BTU/h) = conditioned area × heat-loss factor × adjustment factor
| Input | Practical note |
|---|---|
| Conditioned area | Use the floor area served by the proposed system, excluding unconditioned zones; area alone does not describe the building load. |
| Load factor | This user-supplied BTU/h-per-square-foot factor controls the screening load directly. It is not derived from the envelope or weather by this tool. |
| Ceiling/climate factor | Use this multiplier only for an adjustment you can justify; it combines effects that a full load calculation would model separately. |
Worked heat loss example
Heat Loss Estimator example: 364 ft² × 25 BTU/h·ft² × 1.1 = 10,010 BTU/h, equivalent to 2.93 kW of heat rate.
Treat BTU/h as a screening result
Use the BTU/h result only as a benchmark and obtain an assembly-by-assembly, room-by-room load before sizing equipment.
What a component heat-loss calculation adds
Envelope assemblies, indoor-outdoor design temperatures, infiltration, ventilation, thermal bridges, slab edge, ducts, and adjacent spaces control real heat loss.
Questions specific to this calculation
What does the heat-loss factor represent?
It is a combined screening assumption in BTU/h per square foot. Because it bundles climate and building performance into one number, changing it can move the result substantially.
What information is missing from this simplified heat-loss model?
The tool does not separately calculate walls, roofs, floors, windows, doors, infiltration, ventilation, ducts, or indoor and outdoor design temperatures. Use a recognized load method for design.
For a component-based residential heat-loss calculation, use a method such as ANSI/ACCA Manual J; the area-factor model on this page is only a screen.