Hvac planning tool

HVAC Size Planning Calculator

Planning estimate only — not Manual J and not equipment selection. Enter low/high design-load densities from a qualified assessment or source; this tool supplies no density default or local requirement.

User-supplied load planning

Plan an HVAC load range

Planning estimate only — not Manual J and not equipment selection. This arithmetic does not recommend a load density, delivered capacity, catalog size, or equipment.

Conditioned area (sq ft)Total conditioned floor area in square feet from your project scope.

User-supplied low design-load density (Btu/h/ft²)Enter the low density from your qualified assessment or identified source. This tool provides no recommended value.

User-supplied high design-load density (Btu/h/ft²)Enter the high density from the same qualified assessment or identified source; it cannot be lower than the low value.

I acknowledge that both density values came from my identified qualified assessment or source.Required provenance control. The tool does not supply, recommend, or verify these values.

Known additional loads

Add only separately known Btu/h loads not already represented in your density range, so they are not double counted.

Optional; up to 20 labeled loads.

User-supplied equipment derating (%) — optionalOptional arithmetic only, up to 90%. The source load is divided by (1 − derating/100): for example, 10% means divide by 0.90. Results use whole Btu/h and independently rounded 0.001 nominal-ton outputs; no equipment or site derating is inferred.

Plan responsibly

Before You Build

This project may be subject to local permit, zoning, site, or structural requirements.

Require qualified load analysisVerify project-specific load inputs through qualified local analysis.
Require equipment reviewVerify equipment performance, controls, utilities, venting, and installation separately.
Verify local requirementsConfirm adopted code, amendments, permits, inspections, and manufacturer requirements locally.

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

How we calculate this

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.

planning Btu/h = (area × entered density + Σ separately known loads) ÷ (1 − entered derating/100); nominal tons = planning Btu/h ÷ 12,000

Do not double count known loads

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.

Treat derating as user-supplied arithmetic

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.

Get qualified local design

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

HVAC Size Planning Calculator examples

1,400 sq ft with no additions

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.

Known load and 10% user-entered derating

For the worked input, the pre-derating range is 35400–46200 Btu/h and the planning range is 39333–51333 Btu/h.

Common questions

HVAC Size Planning Calculator FAQ

Is this a Manual J calculator?

No. It is user-supplied planning arithmetic and does not calculate the project-specific inputs required for Manual J.

Does equivalent nominal tonnage select equipment?

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.

Where do the density values come from?

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.

What does equipment derating mean here?

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.

Does this account for occupants and internal gains?

No. Occupant and internal gains require qualified project-specific load analysis; this tool only combines values you enter.

Sources

Assumptions and references

NIST Guide to the SI, Appendix B.9: Primary conversion reference defining one ton of refrigeration as 12,000 Btu (IT) per hour. Last checked 2026-08-24.
ACCA — Manual J Residential Load Calculation: Primary boundary source showing that residential load calculation is a detailed procedure, not area-times-density planning arithmetic. Last checked 2026-08-24.
ACCA — Manual S Residential Equipment Selection: Primary boundary source separating equipment selection, manufacturer performance data, and design conditions from this arithmetic. Last checked 2026-08-24.
U.S. DOE Building America — Accurate Heating and Cooling Load Calculations: Primary guidance describing project-specific load inputs and the separate HVAC design sequence. Last checked 2026-08-24.

Last reviewed: 2026-08-24