HVAC Tools

Free HVAC and air-conditioning calculators that run entirely in your browser — AC tonnage and BTU load, BTU↔tons, CFM from tonnage and air changes, duct sizing, delta-T, SEER running cost, dehumidifier and ventilation sizing, furnace AFUE and superheat/subcooling. Estimates only, nothing uploaded.

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AC Tonnage / Cooling Load Calculator

Estimate the cooling BTU/hr and air-conditioner size in tons for a room or home from floor area, climate, occupants, sun exposure and kitchen load.

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Furnace / Heating BTU Size Calculator

Estimate the heating BTU/hr output needed and the required furnace input rating from floor area, U.S. climate zone, insulation quality and AFUE.

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BTU ⇄ Tons of Cooling Converter

Convert cooling capacity between BTU/hr, tons of refrigeration and kilowatts using the 12,000 BTU/ton HVAC standard, with a handy equivalents table.

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CFM per Ton Airflow Calculator

Find required airflow (CFM) from cooling tonnage using the standard 400 CFM/ton rule, with dry and humid climate adjustments, plus a reverse mode.

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CFM from Air Changes per Hour (ACH)

Convert a target ventilation rate (air changes per hour) into required airflow in CFM for a room of given size, or find the ACH a known CFM delivers.

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Duct Size Calculator (Round & Rectangular)

Find the round duct diameter or rectangular dimensions to carry a given CFM at a target velocity, plus the ASHRAE equivalent-round of a rectangular duct.

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HVAC Delta-T (Supply/Return Split) Health Check

Check your AC or furnace by the temperature split between return and supply air. Flags whether cooling delta-T (16–22°F) or heating rise is in range.

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SEER / SEER2 Cooling Cost & Savings Calculator

Estimate annual AC electricity cost from SEER or SEER2, tonnage, runtime, and your kWh rate — and see the yearly savings and payback of a higher-efficiency upgrade.

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Dehumidifier Size Calculator (Pints/Day)

Find the dehumidifier size in pints per day for any room from its square footage and how damp it feels, mapped to the nearest 20/30/50/70-pint unit class.

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Whole-House Ventilation Calculator (ASHRAE 62.2)

Calculate the continuous mechanical ventilation airflow (CFM) a home needs for indoor air quality per ASHRAE 62.2: 0.03 × floor area + 7.5 × (bedrooms + 1).

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Furnace AFUE Efficiency & Fuel Cost Calculator

Convert furnace input BTU to usable output at a given AFUE and compare annual fuel cost and savings between two efficiency levels for gas, propane, or oil.

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Superheat & Subcooling Refrigerant Charge Calculator

Calculate actual superheat and subcooling from line temps and pressures for R-410A, R-22, R-32, or R-134a, and compare to targets to check the refrigerant charge.

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