CFM stands for cubic feet per minute, the volume of air moved per minute by a fan, duct or diffuser. It determines how much conditioned air reaches a room and is central to ventilation, cooling and comfort. In metric design the equivalent is cubic metres per hour or litres per second, where one CFM equals about 1.699 cubic metres per hour. Getting the CFM right ensures a space receives enough fresh and conditioned air.

Important HVAC Terms Explained + Free HVAC Unit Converter (MEP Guide)

Q: What is a ton of refrigeration (TR) in HVAC?

A ton of refrigeration, written TR, is a unit of cooling capacity equal to 12,000 BTU per hour or about 3.517 kilowatts. It originally represented the cooling produced by melting one ton of ice over 24 hours. MEP consultants use it as the standard way to state the size of air conditioners and chillers, so a building might be described as needing, for example, 100 TR of cooling. Converting between TR, kilowatts and BTU per hour is one of the most common calculations in HVAC design.

Q: What is static pressure in HVAC?

Static pressure is the resistance that a fan must overcome to push air through the duct system, including the ducts, bends, filters and diffusers. It is measured in inches of water gauge in imperial units or in pascals in metric units, where one inch of water gauge equals about 249 pascals. Higher static pressure means the fan needs more power, so controlling it keeps energy use and noise down while still delivering the required airflow.

Q: Why do project owners need to understand HVAC terms?

Understanding basic HVAC terms helps project owners, architects and other stakeholders follow what MEP consultants propose, review designs, and make informed decisions about cost, comfort and energy use. When an owner knows what a ton of refrigeration, CFM or static pressure means, discussions about system sizing, running cost and efficiency become much clearer, and it is easier to compare options and avoid over or under sized systems.

Q: How do I convert TR to kW?

To convert a ton of refrigeration to kilowatts, multiply the number of tons by about 3.517, because one ton of refrigeration equals 3.517 kilowatts of cooling. For example, a 50 ton chiller provides about 175.8 kilowatts of cooling. To go the other way, divide the kilowatts by 3.517 to get tons. The HVAC unit converter on this page does this instantly, along with airflow, pressure, temperature, velocity and power conversions.

Q: What units do MEP consultants convert most often?

MEP consultants most often convert cooling capacity between tons of refrigeration, kilowatts and BTU per hour, airflow between CFM, cubic metres per hour and litres per second, pressure between inches of water gauge and pascals, temperature between Celsius and Fahrenheit, air velocity between metres per second and feet per minute, and power between horsepower and kilowatts. These conversions come up constantly when working across imperial and metric drawings and equipment data, which is why a quick converter is so useful.

Ever sat in a project meeting where the HVAC consultant rattles off "we need 120 TR, 40,000 CFM at 2 inches static" — and half the room quietly nods without a clue? HVAC is full of jargon that MEP consultants use daily but owners, architects and clients rarely understand. This guide fixes that: a plain-English glossary of the most important HVAC terms so everyone can follow the conversation — plus a free HVAC Unit Converter for the conversions consultants do constantly (TR ↔ kW, CFM ↔ m³/hr, inWG ↔ Pa, and more).

The HVAC Unit Converter
Why These Terms Matter
Cooling Capacity Terms
Airflow & Pressure Terms
Equipment Terms (AHU, FCU, VAV…)
Efficiency & Heat Terms
Quick Conversion Table
FAQ

The HVAC Unit Converter

Pick a category, type a value, and get the converted result instantly. Built for the imperial↔metric conversions MEP consultants use every day.

 HVAC Unit Converter

Cooling · airflow · pressure · temperature · velocity · power

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Validation note: the converter uses standard HVAC factors — 1 TR = 12,000 BTU/hr = 3.517 kW; 1 CFM = 1.699 m³/hr = 0.472 L/s; 1 inWG = 249.09 Pa; 1 m/s = 196.85 fpm; 1 HP = 0.746 kW — all matching engineering references.

Why These Terms Matter to Everyone on a Project

MEP (Mechanical, Electrical, Plumbing) consultants design the HVAC that keeps a building comfortable and healthy. But their language — TR, CFM, static pressure, AHU, VAV — can leave owners and architects guessing. Understanding these terms helps you review designs, compare options, question over-sizing, and grasp running costs. You don't need to be an engineer — just to know what the key words mean.

Cooling Capacity Terms

Ton of Refrigeration (TR)

The standard measure of cooling capacity — how much heat a system can remove. 1 TR = 12,000 BTU/hr ≈ 3.517 kW. A building might need "120 TR." Convert: TR ↔ kW ↔ BTU/hr above.

BTU/hr

British Thermal Units per hour — a heat-flow unit for heating/cooling capacity. 12,000 BTU/hr = 1 TR. Common on equipment data sheets.

Cooling Load

The total heat that must be removed to hold a room at its design temperature — from weather, people, lights, equipment and the building fabric. It sets the required TR. Estimate it with our HVAC AC load calculator.

Chiller / Chilled-Water System

A central plant where a chiller cools water that's pumped to AHUs and FCUs around the building to absorb heat. Sized in TR — see the chiller tonnage calculator.

Airflow & Pressure Terms

CFM (Cubic Feet per Minute)

The volume of air a fan, duct or diffuser moves per minute — how much conditioned air a room gets. Metric: m³/hr or L/s (1 CFM ≈ 1.699 m³/hr). Size it with the CFM calculator.

Static Pressure

The resistance the fan must overcome to push air through ducts, bends, filters and diffusers. Measured in inches of water gauge (inWG) or pascals (1 inWG ≈ 249 Pa). Higher static = more fan power.

Air Velocity

How fast air moves in a duct or from a diffuser (m/s or fpm). Too high = noise and draughts; too low = poor throw. 1 m/s ≈ 196.85 fpm.

Pressure Drop

The static-pressure lost as air flows through the system — the fan must make it up. Managing it keeps energy and noise low. The same idea applies to pipes in the pressure drop calculator.

Equipment Terms

AHU — Air Handling Unit

A large box with fans, coils, filters and dampers that conditions and circulates air for a zone or building. The workhorse of central HVAC.

FCU — Fan Coil Unit

A smaller local unit (fan + coil) that heats/cools one room or zone — common in hotels and offices.

VAV — Variable Air Volume

An energy-saving system that varies the amount of air to each space with its changing load (instead of changing air temperature). Saves fan energy at part load.

Ductwork & Diffusers

Ducts carry air; diffusers/grilles deliver it into the room in the right direction and quantity. Their sizing controls comfort, velocity and noise.

Efficiency & Heat Terms

Sensible & Latent Heat

Sensible heat changes air temperature (what a thermometer reads); latent heat changes air moisture. HVAC handles both — explore this in the psychrometric calculator.

COP & EER

Efficiency measures: Coefficient of Performance and Energy Efficiency Ratio — how much cooling you get per unit of electricity. Higher = cheaper to run.

U-value / R-value

How much heat the building envelope lets through (U-value) or resists (R-value) — a big driver of cooling load. Check the U-value / R-value calculator.

Quick Conversion Table

Quantity	Imperial	Metric
Cooling capacity	1 TR = 12,000 BTU/hr	3.517 kW
Airflow	1 CFM	1.699 m³/hr = 0.472 L/s
Static pressure	1 inWG	249.09 Pa
Air velocity	1 m/s	196.85 fpm
Power	1 HP	0.746 kW
Temperature	°F = °C×9/5 + 32	K = °C + 273.15

Authoritative external reference: ASHRAE (HVAC standards and terminology).

Frequently Asked Questions

What is a ton of refrigeration (TR) in HVAC?

A unit of cooling capacity: 1 TR = 12,000 BTU/hr ≈ 3.517 kW. It's the standard way MEP consultants size air conditioners and chillers.

What is CFM in HVAC?

Cubic Feet per Minute — the air volume a fan/duct/diffuser moves per minute. 1 CFM ≈ 1.699 m³/hr. It sets how much conditioned air a room receives.

What is static pressure in HVAC?

The resistance a fan must overcome to push air through ducts, filters and diffusers, in inWG or Pa (1 inWG ≈ 249 Pa). Higher static = more fan power.

Why do project owners need to understand HVAC terms?

So they can follow consultants' proposals, review designs, judge cost and efficiency, and avoid over- or under-sized systems — without being engineers.

How do I convert TR to kW?

Multiply TR by 3.517 (1 TR = 3.517 kW). A 50 TR chiller ≈ 175.8 kW. The converter above does it instantly.

What units do MEP consultants convert most often?

Cooling (TR/kW/BTU-hr), airflow (CFM/m³-hr/L-s), pressure (inWG/Pa), temperature (°C/°F), velocity (m/s/fpm) and power (HP/kW).

Conclusion

HVAC doesn't have to be a foreign language. Once you know that TR is cooling size, CFM is airflow, and static pressure is what the fan fights, MEP design discussions suddenly make sense — and better decisions follow. Bookmark the HVAC unit converter above for the daily TR↔kW, CFM↔m³/hr and inWG↔Pa conversions, and share this glossary with anyone on your project who needs to speak the language.

For more HVAC, building energy and simulation tutorials plus free engineering calculators, explore Free CFD Tutorial. If this helped, please share it with your project team and fellow consultants.

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