A British Thermal Unit, or BTU, is an international energy measurement. By definition, a British Thermal Unit is the amount of heat needed to raise one pound of water, 1° Fahrenheit. Why is this important? Knowing the amount of energy, measured in BTU’s, is necessary to keep your home comfortable in the both heating and cooling seasons.

Most people think the term “air conditioning” implies cooling the air inside a building.To many industry professionals, “air conditioning” means altering the environment within a building to make it more comfortable. This could mean cooling the air in the hot weather or heating the air in colder temperatures. It could mean reducing humidity levels. Or in more pleasant weather conditions, simply exchanging the inside air with fresh, outdoor air.

It’s all about the amount of energy required to “condition” the air.  And it’s all about the BTU’s needed to get the job done. While air conditioning during hot weather, BTU’s measure the amount of heat a system can remove from your home each hour.  Usually a British Thermal Unit or BTU, is thought of in the heating sense of the definition. That is, how much energy to make the indoor air temperature more comfortable.

There are several online resources with estimated BTU calculators. For your convenience, your WE LOVE FIRE expert has included three for your consideration. The first two are merely “rules of thumb” that are often handy during our conversations with customers.

The first technique is to simply figure the square footage of the space you want to heat. In warmer climates, multiply this number by 10 – 15. In more moderate climates, multiply by 20 – 30. And in cold climates multiply the square foot number by 30 – 40. For example, if you’re trying to heat 1000 square feet in a cold climate, 30,000 – 40,000 BTU’s will add significant warm air to your home when heating with a gas appliance. 60,000 – 80,000 when heating with a wood appliance.

Another quick and easy way to estimate the number of BTU’s required is with this helpful chart:


APPROXIMATE SQUARE FOOTAGE Up to 200 Up to 400 Up to 600 Up to 800 Up to 1000 CALCULATE THE BTU YOU NEED HERE!
RECOMMENDED INSULATION 4,000 BTU 8,000 BTU 12,000 BTU 16,000 BTU 20,000 BTU
MODERATE INSULATION 6,000 BTU 12,000 BTU 18,000 BTU 24,000 BTU 30,000 BTU
POOR INSULATION 9,000 BTU 18,000 BTU 27,000 BTU 36,000 BTU 45,000 BTU


This chart is based on a ceiling height of 9 feet or less. Obviously, there are several other variables that are difficult to quantify when estimating the energy required to heat your space. Understand that these are rough estimates only and that actual BTU’s will depend on several factors: the number of windows, the climate, the age of the building, orientation to the south, the type and amount of insulation, construction techniques, etc.

By design, the third BTU calculator is much more detailed and takes many of these variables into consideration. Calculate how many BTUs you need to heat a room or even a house with a wood-burning, pellet or gas fireplace, insert or stove. This BTU Calculator will determine what hearth product size is required with only a few steps and information such as square footage (sq ft). Most of the other online calculators relate to central heating and/or air conditioning systems. Our BTU calculator is the best there is for fireplaces, stoves and inserts. It’s been developed by fireplace industry experts.

Another point worth mentioning, when calculating BTU’s required for an entire home, the calculation must include the “worst case scenario”. For example, the coldest temperatures of the year might be -30° F. Maybe it gets that cold only once or twice a year. Perhaps, only once every five years. But the primary heating system must have the ability to warm the house from -30° F to 70°F to keep your family comfortable. That’s a 100°F temperature swing!

If a fireplace, stove or insert is normally used as a supplement heat source or used to zone heat the house, the temperature difference might only be 15°F – 25°F.

These variables are the main reason that manufacturers make equipment that is versatile and easy to use. For instance, adjustable gas valves and remote controls for fireplaces, inserts and stoves. These controls easily vary the amount of natural or LP gas that’s burned, or the energy in BTU’s delivered to the room. Less gas means less heat. And less gas means less energy in BTU’s.

Similarly, secondary combustion technology and easy to use air controls are used to regulate the amount of energy delivered with today’s wood burning equipment.

So, click on our calculator above and see what the needs are for your home. Your WE LOVE FIRE expert would love to continue this conversation with you! We’ll look forward to providing you with worthwhile information and great service . . .  above and beyond your expectations!