HVAC Load Calculator
Gives a rough cooling load estimate in BTU per hour and tons from floor area, number of occupants, and number of windows, using 25 BTU per square foot plus 400 BTU per occupant plus 1000 BTU per window. It is a simplified rule-of-thumb, not a full Manual J load calculation.
What this calculator does
The HVAC Load Calculator estimates your result instantly from the values you enter, using standard construction & home formulas. Gives a rough cooling load estimate in BTU per hour and tons from floor area, number of occupants, and number of windows, using 25 BTU per square foot plus 400 BTU per occupant plus 1000 BTU per window. It is a simplified rule-of-thumb, not a full Manual J load calculation. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.
Result
About HVAC Load Calculator
This HVAC load calculator gives a quick cooling load estimate. It adds 25 BTU per hour for each square foot of floor area, 400 BTU per occupant, and 1000 BTU per window, then converts the total to tons by dividing by 12,000 BTU per ton.
This is a simplified rule-of-thumb suitable for a ballpark figure. A true Manual J load calculation also weighs insulation, climate, orientation, and air sealing, which this tool does not.
Formula & Mathematical Calculation
Estimated Cooling Load (BTU/hr) = f(Area (ft²), Occupants, Windows)
Calculated according to standard construction formulas implemented in the calculator core.
Calculation Example
For a 2000 ft² home with 4 occupants and 10 windows:
- BTU/hr = 2000 × 25 + 4 × 400 + 10 × 1000 = 50,000 + 1,600 + 10,000 = 61,600 BTU/hr
- Tons = 61,600 ÷ 12,000 ≈ 5.13 tons
Key Benefits
- Gives a fast ballpark cooling load in both BTU per hour and tons
- Factors in occupants and windows, not just floor area
- Converts the BTU total to tons using 12,000 BTU per ton
- Useful as a sanity check before a detailed load calculation
How to Use this Calculator
-
Enter the area
Type the conditioned floor area in square feet into the Area (ft2) field, for example 2000. -
Enter the occupants
Type the number of people into the Occupants field, for example 4. -
Enter the windows
Type the number of windows into the Windows field, for example 10. -
Calculate
Press Calculate to see the estimated cooling load in BTU per hour and in tons.
Assumptions & Limitations
What the calculation assumes
- Every value you enter is treated as an exact, known amount.
- Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
- Results use standard published formulas and account only for the values entered above.
- Rounding is applied for display; the underlying calculation uses your full precision.
- Results are returned in the same units you enter, unless the tool states the output unit.
What it does not cover
- HVAC Load Calculator produces a calculated result for reference and learning, not a certified or official measurement.
- Real-world outcomes differ when tolerances, rounding rules or local standards apply.
- Definitions and standards vary by region and change over time; verify the convention that applies to your case.
- Figures are only as accurate as the inputs you supply — check them before acting on the result.
- For work where the result carries real consequences, confirm it against an authoritative source.
Frequently Asked Questions
Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.