When it comes to your home’s heating and air system, many vague or confusing terms might emerge on your visit with an in-home HVAC technician. Not to mention, if you have ever bought a portable heater or air conditioner, there are many numbers and abbreviations on the product spec sheet that seem like you’d need an electrical engineering degree to understand. While our technicians have excellent customer services skills and will always take the time to explain foreign topics to you, we also realize that many homeowners like to do their research. One, often confusing, piece of terminology that we get asked about quite frequently is regarding BTUs: what they are and how they affect the typical homeowner. The concept of BTUs is rooted in chemistry and is quite interesting. This article will cover then, in-depth, what are BTUs?

Definition: BTUs

BTU stands for British Thermal Unit. As you might have guessed from the use of the word thermal, a BTU is a standard unit of measurement for heat. Specifically, a British Thermal Unit is the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. Oddly enough, Americans are usually better acquainted with the BTUs metric counterpart: the calorie. For example, a heating unit with 10,000 BTUs produces 10,000 BTUs of energy in an hour. The correct measurement for central heating and air units is the BTU per an hour rating; however, most spec pages for HVAC units simply refer to this rating as BTUs.

BTU: Other Uses

BTUs are primarily used to define the energy content for natural gas, as well as a unit of power for HVAC systems. BTUs are also associated with cooling in refrigeration and air conditioning applications. Furthermore, BTUs describe thermal insulation performance and are also used to express the conversion efficiency of heat into electricity. So, you see, BTUs are a fairly widely used term when it comes to energy, but we want to know how they affect YOU and your HVAC unit directly.

BTUs and Air Conditioning

Your air conditioning unit works by removing heat from a room using a compressor system. Air compressors utilize chemical refrigerant to absorb the heat and blow it outside. When discussing air conditioning units, BTUs are used to describe the amount of heat an air conditioner can remove using its compressor.

BTUs and Heating Systems

The BTU is used to measure the overall heat output of your heating system. The higher the BTU of a heating system, the faster it can raise the temperature in your space over the span of an hour, or to heat a larger area.

BTUs: How Many Do I Need?

When purchasing a new HVAC unit or furnace (or even just a space heater or in-window air conditioning unit), one of the first decisions you’ll make is the BTU rating of your new heating and air unit. The number of BTUs you will need in your heating or cooling system derives from the size of the rooms you need to heat up or cool down. Below is an essential reference chart to help steer you towards the correct unit with just the right amount of BTUs.

BTU Calculator

Use this calculator to estimate the BTU ratings you need for a window air conditioner or central air conditioner

Room Length (in ft.)
Room Width (in ft.)
Room Height (in ft.)
Insulation Condition
Min. BTU’s Needed:

It’s important to understand that purchasing a new HVAC unit with more BTUs than you actually need is counterproductive and could be considered a waste of energy. The reason being, a higher BTU level than your square footage needs will tend to cycle on and off more often, which can also decrease the overall lifespan of your HVAC unit. If you buy a unit with a lower BTU rating than your square footage needs, it will run continuously, never reaching the desired temperature, and cause the unit to experience too much of a heat load. A lower BTU rating can burn out your unit far earlier than the manufacturer’s specifications.

Aside from the square footage of your house, other factors you want to take into consideration when determining the proper BTU level needed are the height of your ceilings, the typical climate where you live, the location of your HVAC unit in relation to the rooms it will service, the rating of your insulation, the energy efficiency of your windows, and your overall home shape.

Consult an HVAC Professional

Many factors go into choosing an HVAC unit with the correct amount of BTUs for your home. Contacting a Knoxville HVAC professional will not only help you select the perfect unit but can also remove an old HVAC unit install the new unit and provide preventative maintenance to ensure it lasts for years to come. City Heating and Air provides all heating and cooling services and repairs throughout Knox County. Contact us at (865) 938-1005 or by email at info@wordpress-587374-4313908.cloudwaysapps.com for assistance with your HVAC needs.