Free tool · Whole-house block load
HVAC load calculator
Four quick steps: location, construction, windows and systems. Get heating and cooling BTUs, tonnage, a line-by-line breakdown and a one-page PDF.
Estimated cooling
0 Btuh · 0 sensible + 0 latent · SHR 0
0 sq ft per ton
Btuh breakdown
| Component | Sensible | Latent | Heating |
|---|
Change any input above and the numbers update instantly.
How this estimate works
It is a whole-house block load. Each part of the envelope is assigned a typical U-value for the construction you picked. Walls, doors and the ceiling use outdoor design temperatures plus a sun and attic allowance. Windows add conduction and solar gain based on which way each side faces and how shaded it is. Air leakage, fresh-air ventilation, people and appliances add sensible and latent heat, and ducts outside the conditioned space add losses.
A real ACCA Manual J does the same work room by room, from your actual plans, window specifications and local design weather. That precision is why building departments require it, and why it often lands well below the rule of thumb.
Questions
How accurate is this calculator?
It is a simplified whole-house estimate using typical design conditions for your climate zone. It is far closer than square-foot rules of thumb, but it is not a Manual J and it will not pass plan review.
Why is it lower than what my contractor quoted?
Most quotes are sized by square footage, often around one ton per 500 square feet. Newer, tighter homes usually need much less. That gap is oversizing, and it costs you comfort, humidity control and money.
Can I submit this for a permit?
No. Building departments that follow the IRC require equipment sized with ACCA Manual S from ACCA Manual J room-by-room loads. We prepare that report.
Does it calculate duct sizes?
No. Duct sizing needs room-by-room airflow from a Manual J. That is what Manual D is for.
Same-day quotes
Ready for the real number?
Drop in the plan set and pick your services. A designer replies with price and turnaround, usually within 30 minutes during business hours.