How to use this estimate
- Zone allocation by equal area is only a starting point; rooms rarely have identical loads.
- Check the outdoor unit’s minimum output so shoulder-season operation is not oversized.
- Long refrigerant runs, elevation changes, and branch boxes affect design.
Transparent method
We expose the planning formula so you can challenge it and replace assumptions with local evidence.
area × 24 BTU/h × climate factor × envelope factor, divided by zonesWhat this calculator cannot see
- Bedrooms, kitchens, glass-heavy rooms, and upper floors need room-by-room calculations.
- Multi-zone outdoor capacity is not always the simple sum of indoor-head labels.
Professional verification
Use this result to prepare questions and compare scenarios. Final equipment selection, electrical work, refrigerant work, combustion, duct design, and permitting should be handled by qualified professionals following local codes and manufacturer instructions.