HVAC Unit Converter

Every conversion routes through BTU/hr as the common base unit. The input is first converted to BTU/hr, then divided out to each target unit. Airflow is excluded because it needs a temperature or enthalpy difference. For sensible air-side heat transfer at standard density, Q = 1.08 × CFM × ΔT. Calculate that separately with the CFM calculator. If you are sizing a system rather than converting a known capacity, start from the tonnage calculator instead.

• Confusing thermal kW (capacity) with electrical kW (power draw) — their ratio depends on operating efficiency; one cannot be inferred from the other without that information
• Using 3,517 W/ton interchangeably with the converter's kW value — that figure is rounded; the exact divisor is 3,412.142 BTU/hr per kW
• Mixing kcalIT/hr and kW from different region spec sheets without converting both to a common base first
• Treating the CFM result as a final duct design — it is a 400 CFM/ton reference, not a Manual D airflow calculation
• Rounding tonnage during conversion — keep exact values for math, and select equipment from design-condition performance rather than a universal half-ton rounding rule
• Ignoring whether a heating rating is fuel input or delivered output: both convert with the same physical factors, but they describe different quantities

The cooling and heating world inherited its vocabulary from several centuries of engineering, and the units never converged on a single standard. In the United States the British thermal unit per hour (BTU/hr) remains the working currency: a BTU is a quantity of heat, approximately that needed to raise one pound of water one degree Fahrenheit; BTU/hr is the rate at which that energy is transferred. Equipment nameplates, AHRI certified ratings, and ACCA Manual J load reports all speak in BTU/hr, which is why this converter routes every input through it as the common base.

The "ton" is the most quietly historical unit on the dial. It does not measure weight — it measures the cooling effect of melting one short ton (2,000 lb) of ice over 24 hours. The latent heat of fusion of ice is about 144 BTU per pound, so 2,000 lb × 144 BTU ÷ 24 hours lands on the familiar 12,000 BTU/hr that defines one ton of refrigeration. That ice-house heritage is why a residential split system is sold as a 2-, 3-, or 5-ton unit rather than by a metric figure, and why tonnage maps cleanly onto the airflow rule of roughly 400 CFM per ton used throughout this site.

The kilowatt is the unit the rest of the world reaches for. Because 1 kW equals 3,412.142 BTU/hr, a nominal 1-ton system is about 3.517 kW of thermal capacity. The International Table kilocalorie per hour used here has a defined calorie convention. Other conventions differ slightly. Kilocalories per hour persist on spec sheets across parts of Europe, the Middle East, and Asia, where 1 kcalIT/hr equals 3.968321 BTU/hr — so a 12,000 BTU/hr machine is listed as roughly 3,024 kcalIT/hr. Knowing which dialect a given catalog uses is half the battle when comparing imported and domestic equipment.

The single most consequential distinction this tool cannot make for you is whether a kilowatt figure describes thermal capacity or electrical input. A heat pump rated at 10.5 kW of cooling does not draw 10.5 kW from the panel; it might draw 3 kW and move the rest by relocating heat, and that leverage is its coefficient of performance. US efficiency ratings — SEER2, EER2, HSPF2 for heat pumps, and AFUE for combustion furnaces — all encode that same input-versus-output relationship in different ways. When a European data sheet lists both a capacity in kW and a power consumption in kW, treat only the capacity figure as something to convert here, and feed the rest into an efficiency comparison instead.

Combustion heating adds a second trap. A furnace may advertise an input rating and an output rating; the difference is its AFUE. Converting an 80,000 BTU/hr input furnace as though it delivered 80,000 BTU/hr would label 80,000 as delivered heat when an illustrative 80% conversion gives 64,000 BTU/hr. AFUE is a seasonal fuel efficiency; use rated output for design selection rather than treating AFUE as exact peak performance. Always confirm whether a heating BTU number is gross input or net output before converting it to tons or kW.

• US residential and light commercial: tons and BTU/hr dominate, anchored by AHRI ratings and ACCA Manual J/S
• International and chiller markets: kW of thermal capacity, often alongside electrical kW input
• Legacy and some regional catalogs: kcalIT/hr, especially older boiler and packaged-unit literature
• Airflow context: CFM in the US, m³/h or L/s under SI conventions referenced in ASHRAE 62.1 and 62.2 ventilation rates

Converting units is a clerical step, not a sizing decision. The numbers you convert should originate from a defensible load calculation — for homes, an ACCA Manual J heat-gain and heat-loss analysis that accounts for envelope U-values and R-values, infiltration, internal gains, and your IECC climate zone. The ASHRAE Handbook of Fundamentals supplies the underlying thermal property data, while ASHRAE 62.2 sets the residential ventilation rates that drive much of the outdoor airflow a system must condition. Only after that work is done does converting the result into tons, kW, or kcalIT/hr help you shop a catalog.

The 400 CFM per ton figure deserves the same caution. It is a planning shorthand, useful for sanity-checking a blower, but real duct design follows ACCA Manual D and may call for 350 CFM per ton in high-latent climates depending on latent requirements and manufacturer airflow limits; high efficiency alone does not prescribe lower airflow. Once you have a converted tonnage you trust, walk it back through the tonnage calculator to confirm the size against your actual load, and use the CFM calculator for airflow based on a stated temperature difference; final duct design needs its own pressure and distribution analysis. For a deeper tour of how these units relate to one another, the guide to heat load calculation units works through the same conversions with worked examples and the rationale behind each constant.

Treat this converter as the bilingual interpreter between a US tons-and-BTU world and an international kW-and-kcal world. It will tell you that 5 tons, 60,000 BTU/hr, 17.59 kW, and roughly 15,120 kcalIT/hr all describe the same machine — but it will not tell you whether that machine is the right one for your building. Pair the conversion with a proper Manual J load and a verified airflow plan, and the units stop being a source of confusion and become exactly what they should be: a precise, interchangeable description of the same physical capacity.

Using these inputs, with BTU/h selected, the results are heat flow: 36,000 BTU/h; refrigeration capacity: 3 tons; thermal power: 10.551 kW; international table kilocalories: 9,071.847 kcalIT/h. Defaults are example assumptions, not universal design conditions.

• Do not drop the per-hour term when comparing heat-flow capacity.
• A nominal 400 CFM per ton is an assumption, not a unit conversion.
• Use rated capacity at your design conditions for equipment selection; conversion alone cannot verify performance.

Continue with the related calculator for a separate part of the design.

ASHRAE Handbook - Fundamentals provides heat-transfer, air-property and load-calculation background. Example inputs are stated scenarios, not prescribed handbook values.

For residential design, ACCA Manual J, S and D address load calculation, equipment selection and duct design. This calculator does not certify a complete design or code compliance.