Free HVAC load calculator -- estimate cooling and heating BTU
Ballpark cooling tonnage and heating BTU for a customer conversation in under a minute. No signup, no server, no data leaves the device.
HVAC Load Estimator -- enter your job details below. Results update instantly.
Cooling load
--
-- tons
Recommended size: --
Heating load
--
Furnace output: --
This estimate is directional. A full ASHRAE Manual J calculation is required before ordering equipment or pulling permits.
Oversizing alert: a result above 4 tons for a space under 2,400 sq ft often signals an oversized unit. Oversizing by more than 15% causes short-cycling, poor dehumidification, and premature equipment failure. Double-check the inputs and run a Manual J before specifying equipment.
What this HVAC load estimator accounts for
Conditioned square footage -- the total floor area that needs heating and cooling, the single biggest factor in the estimate
Climate zone -- whether the building is in a hot, mixed, or cold climate, since design temperatures drive the load more than square footage alone
Ceiling height -- 8-foot ceilings are the baseline; vaulted ceilings and second-floor additions add meaningful volume to condition
Window area and orientation -- windows gain heat in summer and lose it in winter; south-facing glass in a hot climate can double the cooling load of a small room
Insulation level -- poor insulation (old attic, uninsulated walls) increases load by 20-40%; modern code-built homes run efficient
Occupancy -- each person generates about 400 BTU/hr of internal heat, relevant for small offices or densely occupied spaces
Local design temperatures -- the 1% summer dry-bulb and 99% winter dry-bulb from ASHRAE tables, which define the peak conditions the system must handle
Safety factor and oversizing guidance -- why oversizing by more than 15% causes short-cycling, poor dehumidification, and premature equipment failure
Win HVAC bids faster with Claver
Claver stores the load estimate against the customer record so the first site visit becomes the proposal conversation instead of a callback. When the job closes, the equipment specs and the scope flow into the work order with the same tonnage and model already filled in, and the tech never has to re-enter what was already quoted.
How do I estimate HVAC tonnage without a Manual J?
A rule-of-thumb starting point is 400 to 600 square feet per ton for a well-insulated home in a moderate climate. Adjust up in hot humid climates, down in cold climates with excellent insulation, and always add 15 to 25 percent for high ceilings, large window areas, or south-facing glass. A full Manual J is required for permits and final equipment selection.
Is this calculator really free?
Yes, the HVAC load calculator is free with no signup, no credit card, and no data sent to a server, so the customer and job details stay on the device.
How accurate is this compared to a Manual J?
This calculator gives a directional estimate within 10 to 20 percent of a full Manual J for typical residential construction. It should not be used as the sole basis for equipment selection -- use it for the initial customer conversation and ballpark quote, then run a proper load calculation before sizing and ordering equipment.
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