Hvac planning tool
Use this as a homeowner planning estimate and sanity-check, not Manual J or equipment selection. Enter low and high design-load densities from a qualified assessment or source; this tool supplies no density default or local requirement.
User-supplied load planning
Homeowner planning and sanity-check estimate only. This is not Manual J and not equipment selection. Insulation, windows, climate, and air leakage all affect heating and cooling loads, so the density values must come from a qualified source. This tool does not recommend a load density, delivered capacity, catalog size, or equipment.
Plan responsibly
This project may be subject to local permit, zoning, site, or structural requirements.
General guidance only: This does not establish adopted local law. It is user-entered arithmetic, not a load calculation, equipment selection, or duct design.
Not Manual J: This does not replace a project load calculation.
Not equipment selection: Nominal tons are a unit conversion only, not equipment selection.
Local requirements may differ. No project-specific model-code reference is asserted here.
Methodology
Inputs are limited to hundredth increments. Multiply conditioned area by each user-entered density, add each labeled known load once to both endpoints, and divide by one minus the optional user-entered derating percentage using exact scaled-BigInt arithmetic. Known, source, planning, and derating-effect outputs round half up to whole Btu/h. Each nominal-ton conversion is independently calculated from the exact ratio and rounded half up to 0.001 nominal ton; these public number scales are proven safe throughout the accepted input bounds.
Insulation slows heat loss and heat gain. Windows can add heat gain in summer and heat loss in winter. Climate affects how much heating and cooling the home needs, while air leakage adds load by letting outdoor air in. Because those details are project-specific, Advanced density values must come from a qualified source.
Enter only labeled loads that are not already represented in the source density range. A single entered Btu/h value is added once to both endpoints.
A 10% entry means nominal capacity is treated as delivering 90% of nominal. The tool does not infer derating from altitude, climate, fuel, voltage, equipment, or model number.
Orientation, envelope, infiltration, ventilation, occupant and internal gains, ducts, sensible and latent load, climate design conditions, actual equipment performance, electrical/fuel scope, code, permit, and inspection require qualified local analysis.
Worked examples
At user-entered densities of 20–28 Btu/h/ft², the source and planning range is 28,000–39,200 whole Btu/h; the exact-ratio 12,000 conversion rounds independently to 2.333–3.267 nominal tons.
For the worked input, the pre-derating range is 35400–46200 Btu/h and the planning range is 39333–51333 Btu/h.
Common questions
No. It is user-supplied planning arithmetic and does not calculate the project-specific inputs required for Manual J.
No. It is a unit conversion only using exactly 12,000 Btu/h per nominal refrigeration ton; it is not delivered capacity, a catalog increment, or a recommendation.
You must enter both values from a qualified assessment or source and acknowledge that provenance. The tool provides no default and does not validate the source.
It is an optional percentage you supply. The source load is divided by the remaining-capacity fraction; no climate, altitude, model, or site adjustment is inferred.
No. Occupant and internal gains require qualified project-specific load analysis; this tool only combines values you enter.
Sources
Last reviewed: 2026-08-24
