HVAC Terminology You Should Know: BTU

When shopping for a new HVAC (heating ventilation & air conditioning) unit, you will probably come across the term “BTU”. This commonly used abbreviation for British Thermal Unit is an important factor in your choice of a new furnace or air conditioning unit, but many do not know what BTU means, or its implications. Read on to learn more about what is a BTU, and why BTUs matter when shopping for a new heating or cooling unit.


What Does BTU Mean?

An HVAC system’s capacity is measured in BTUs, indicating how powerful the unit is. The higher the BTU rating, the more powerful it is. This is not to be confused with energy efficiency, which is measured differently.

In technical terms, a BTU is a measure of heat. It is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. One BTU equals about 1,055 of heat.

In more practical terms, a BTU or British Thermal Unit lets you know how much heat (or energy) your unit is capable of producing. The higher the number, the more heat it can produce.

In a furnace or a heat pump, the number of BTUs refers to the heat output of the particular unit. In an air conditioner, the BTU number refers to the amount of heat removed from the air. Essentially, if you have a larger home, you will require air systems with a higher number of BTUs to heat or cool it effectively and efficiently.


How Does the Number of BTUs Matter When Shopping for a Heating or Cooling System?

When choosing a new HVAC system for your home, it must be sized correctly. When shopping for a new heating and cooling system, you need to find a unit capable of generating the correct number of BTUs for your space. By having the wrong size (number of BTUs) HVAC system installed in your home, you could face frequent repairs, mold issues, and more, all on top of a poorly heated or cooled home.

You want an HVAC system that can produce enough heated air or cooling for the size of its space. If your unit has too few BTUs, not only will your home be cold in the winter, but your unit will be forced to run longer and harder than it ought to, negating any high efficiencies, creating strain on the system, and inviting breakdowns. You’ll also consume more energy than necessary and subsequently pay more each month in energy bills.

If your heating & cooling system is too large or has too many BTUs for your space, its temperature controls will cause the system to shut off too soon, placing great stress on your furnace, dramatically shortening its lifespan.

Because your air conditioning system removes moisture from the air, a system that turns off too quickly will not have the opportunity to remove enough moisture. This will not only leave you feeling sticky in the summer but also create an opportunity for that moisture to create mold in your home.


How Many BTU’s Do I Need?

There is no one-size-fits-all approach to determining how many BTU per square foot your home requires. In general, if you multiply your home’s square footage by 40, you can arrive at a ballpark for the number of BTUs you should be looking for. However, several variables will affect the final size of the unit.

  • Typically, housing square footage numbers do not include the basement, but you should include this area too.

  • If you’ve renovated your attic and are using it as living space.

  • The number of floors in your home.

  • The type and quality of insulation in your home – if your home is not well insulated, it will lose its heated or cooled air more quickly.

  • The age of your home. For example, an older, double-bricked home may have no insulation at all.

  • The size and quality of windows in your house.

  • How your home's floorplan is laid out; it is easier to maintain the temperature in smaller rooms than in an open-concept style of home.

  • Where your home is located; are temperatures extreme or moderate?

  • The height of your home’s ceilings.

These will all impact the size of the furnace or air conditioner you need and the BTU rating of the unit.


A professional HVAC technician or salesperson has the expertise to guide you through this decision and can be a great help in determining the correct size of the HVAC System required for your home.