HVAC tonnage calculator

Non-positive conditioned area is rejected with a clear invalid_input error instead of inventing a load from zero or negative square footage.

How whole-home AC tonnage is estimated from area and climate

When you already know a custom climate factor from a local code table or a prior load sheet, send climate_factor directly and it overrides the zone table. The response reports cooling_btu as area times the factor, tons as cooling_btu divided by twelve thousand, recommended_tons as that value rounded up to the next half-ton equipment step so you can match common two-ton, two-and-a-half-ton, three-ton, and larger nominal sizes, and sqft_per_ton as twelve thousand divided by the factor so you can sanity-check against contractor rules of thumb such as one ton per five hundred to six hundred square feet. This is shopping and planning guidance, not a Manual J calculation with insulation R-values, window SHGC, duct leakage, infiltration, or design dry-bulb temperatures; treat the output as a transparent starting point and let a licensed load study or manufacturer software refine the final equipment selection.

How to call the API and what comes back

Prefer sending numbers rather than pre-formatted strings when you control the client; when you must send strings, avoid unit suffixes or thousand separators that would fail the finite-number pattern. Send a JSON body with required sqft in conditioned square feet (aliases area, conditioned_sqft, square_feet, floor_area, conditioned_area) and optional climate_zone as an integer from one to eight (aliases zone, iecc_zone, climate; default four for a mixed climate when neither zone nor factor is given) or optional climate_factor as a positive BTU-per-square-foot intensity (aliases btu_per_sqft, factor, load_factor, btu_factor). When climate_factor is present it wins; climate_zone is still echoed if you send both so audits can record the zone you had in mind. Square footage must be a finite positive number within the published absolute range so intermediate products remain finite in IEEE double precision on the Worker and in the browser. Non-positive sqft is the primary hard error this capability advertises: zero or negative conditioned area cannot define a whole-home cooling load and returns invalid_input. Climate zone must be a whole number in one through eight; climate_factor must be positive and within absolute limits. On success the response echoes rounded sqft and climate_factor, publishes factor_source as climate_zone or climate_factor, climate_zone and climate_label when a zone is known, cooling_btu and btu (same total), tons, recommended_tons, sqft_per_ton, btu_per_ton as twelve thousand, unit as tons, formula as the human-readable equation string, message as a short English summary, and steps as an ordered array of substitution lines. Failed validation—missing sqft, non-finite numbers, non-positive area, invalid zones, or values outside absolute limits—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item.

Practical tips, limits, and related searches

Measure conditioned floor area as the sum of finished spaces that the central system cools—exclude unconditioned garages, porches, and unfinished basements unless those volumes are on the same supply air path. Convert square metres first by multiplying by about ten point seven six before calling if your plans are metric. Keep dimensions inside the published absolute range so products cannot overflow into non-finite results the solver must reject. Prefer this capability when you already know conditioned area and climate intensity and only need transparent tonnage with a half-ton equipment step; if your source is a multi-zone Manual J, trust the engineered loads over this rule of thumb. Pick the climate zone from an IECC map or local energy code for your site, or paste a custom climate_factor when a contractor or prior Manual J already quotes BTU per square foot. When teaching or writing tests, pair a default zone-four two-thousand-square-foot house with a hot-zone and a custom-factor case, and include a deliberate zero or negative sqft to prove the invalid_input path. This landing targets people searching for an HVAC tonnage calculator, air conditioner tons by square feet, climate zone cooling load, or whole-home AC size online; it is not a room window-unit BTU tool (use the room air conditioner BTU calculator for that intent), not a pure unit converter among tons and kilowatts, not a heat-pump heating sizer, and not a duct or SEER cost estimator. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when you deliberately send sqft zero to verify error handling. Round-trip checks are easy: recompute sqft times the published climate_factor, divide by twelve thousand, ceil to the next half ton, and confirm the published tons and recommended_tons match within the same twelve-decimal rounding used for all numeric fields.