HVAC Unit Conversions

🌡️ Temperature

Fahrenheit (°F)

°F

Celsius (°C)

°C

Kelvin (K)

K

Rankine (°R)

°R

💨 Airflow

CFM (ft³/min)

CFM

CFS (ft³/sec)

CFS

L/s (liters/sec)

L/s

m³/h

m³/s

💧 Water Flow

GPM (US gal/min)

GPM

GPH (US gal/hr)

GPH

L/min

m³/h

ft³/min

🌣 Pressure

in. w.c. (in H₂O)

in. w.c.

Pa (Pascals)

Pa

psi

ft H₂O

kPa

bar

⚡ Energy

BTU

kWh

Wh

Joules (J)

J

Therms

therms

ton-hours

ton-hr

💡 Power / Heat Rate

BTU/hr

MBH (1,000 BTU/hr)

MBH

Tons of Refrigeration

tons

Watts (W)

W

kW

Horsepower (HP)

HP

📚 Key HVAC Conversion Factors

Relationship	Conversion
1 ton refrigeration	= 12,000 BTU/hr = 3.517 kW = 3,517 W
1 MBH	= 1,000 BTU/hr = 0.2931 kW = 0.08333 tons
1 HP (mechanical)	= 2,545 BTU/hr = 0.7457 kW = 745.7 W
1 therm	= 100,000 BTU = 29.307 kWh = 8.33 ton-hr
1 in. w.c.	= 249.1 Pa = 0.0361 psi = 0.0833 ft H₂O
1 GPM water	= 500 BTU/hr per °F ΔT (sensible factor)
1 CFM air (sensible)	= 1.08 BTU/hr per °F ΔT (sea level)
1 CFM air (latent)	= 0.68 BTU/hr per gr/lb Δω (sea level)

ℹ️ About This Tool

This is a live, bidirectional unit converter for the quantities that come up every day in mechanical design: temperature, airflow, water flow, pressure, energy, and power. Pick a category tab, type a value into any field, and every other field in that category updates instantly. There is no from/to selection to fiddle with.

It is built for moving between inch-pound and SI documentation — reading a European fan curve in Pa and m³/h, checking a chiller rating in kW against a US schedule in tons, or translating a pump duty from L/s to GPM — without hunting for conversion factors.

🔬 Formula & Method

Each category converts through a single base unit. The tool divides your input by its factor to reach the base, then multiplies the base by every other unit’s factor. Temperature is the exception — it uses offset formulas rather than simple ratios.

Temperature	°C = (°F − 32) × 5 ÷ 9 · K = °C + 273.15 · °R = °F + 459.67
Power base	1 ton = 12,000 BTU/hr · 1 kW = 3,412 BTU/hr · 1 HP ≈ 2,545 BTU/hr
Pressure base	1 in. w.c. ≈ 249.1 Pa · 1 psi ≈ 6,895 Pa
Energy base	1 kWh = 3,412 BTU · 1 therm = 100,000 BTU

Conversion factors follow standard ASHRAE Fundamentals unit relations and SI definitions. The sensible factor 1.08 and latent factor 0.68 in the reference table above are sea-level air values and decrease at altitude as air density falls.

❓ Frequently Asked Questions

Which units does this converter handle?

Six categories of HVAC units convert live: temperature (Fahrenheit, Celsius, Kelvin, Rankine), airflow (CFM, CFS, L/s, m3/h, m3/s), water flow (GPM, GPH, L/min, m3/h, ft3/min), pressure (in. w.c., Pa, psi, ft H2O, kPa, bar), energy (BTU, kWh, Wh, joules, therms, ton-hours), and power or heat rate (BTU/hr, MBH, tons, watts, kW, horsepower). Edit any field and the others in that category update at once.

What is 1 inch of water column in Pascals and psi?

One inch of water column equals about 249.1 Pa and 0.0361 psi. Inch-water-column is the standard unit for fan static pressure and duct pressure drop in inch-pound practice. The pressure tab converts it directly to Pa, psi, ft of water, kPa, and bar using a common Pascal base.

How is 1 ton of refrigeration related to kW and BTU/hr?

One ton of refrigeration equals 12,000 BTU/hr, which is 3.517 kW or 3,517 watts. One horsepower equals about 2,545 BTU/hr or 0.7457 kW. The power tab converts BTU/hr, MBH, tons, watts, kW, and horsepower against a shared BTU/hr base so all six stay consistent.

Why is the converter bidirectional?

Each category converts through a single base unit, so editing any field recomputes every other field in that category from that base. This means you never have to pick a from-unit and a to-unit separately. Values display to about seven significant figures to keep round-trip conversions accurate.