Last updated: April 23, 2026
HVAC BTU & tonnage calculator
Pick your SD County climate zone and home profile. Get a calibrated BTU load estimate and AC/heat pump tonnage range — good enough to sanity-check a contractor quote.
Want a real Manual J + Manual S equipment selection? We run both before quoting.
Call (858) 808-6055How this works. Baseline BTU-per-sq-ft is calibrated per SD County climate zone from our own install data. Home age, ceiling height, and climate apply multiplicative adjustments. The result is a sanity-check estimate — an actual install quote starts with a full Manual J load calc per ACCA standards.
FAQ
Is this a real Manual J?
No. A full ACCA Manual J calculation factors in window orientation, shading, infiltration rate, duct losses, and dozens of other variables per ACCA HVAC Design Excellence. This calculator is a well-calibrated estimator — good enough to sanity-check a contractor quote, not good enough to order equipment from.
Why do coastal and inland numbers differ so much?
Coastal San Diego averages 68-72°F most days year-round, so the design cooling load is driven by humidity + solar gain more than raw sensible heat. East County and inland hot zones see 100°F+ for weeks, which is a pure sensible-heat load and drives BTU requirements up nearly 2x.
Does this work for heat pumps?
Yes — in SD County, a heat pump sized for cooling is almost always correct for heating too, because our heating loads are a fraction of cooling loads. Exception: backcountry at elevation (Julian, Pine Valley) where heating loads can rival cooling. We size those separately.
Do I need a Manual S equipment selection too?
Yes, if you're actually installing. Manual S takes the Manual J load and matches it to specific equipment (not just tonnage). For a cost estimate, tonnage + SEER2 rating is enough to get in the right price band.
What about two-story homes?
This calculator assumes single-story or uniform two-story. True two-zone systems — where you want independent upstairs/downstairs control — need separate load calcs per zone and different equipment selection.
Ready for HVAC service that actually answers the phone?
Call for a free quote. Same-day service on most repairs. Next-day install on most replacements.