A 30-second sanity check before you quote a swap. Type square footage and climate, get rough BTU/h heating and cooling. This is NOT a Manual J — for permit-grade sizing, run the full load calc.
Sq-ft-based sizing oversizes 30–50% of the time. For a real spec — windows by orientation, infiltration class, latent load — run the Manual J calculator. Both tools are free.
Run a real Manual J →Dispatch, jobs, estimates, invoicing, memberships, and AI diagnostics in one operating system built for HVAC service teams. Free plan, no credit card.