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How Many BTU Do I Need to Heat A House?

Asking yourself ‘how many BTU do I need to heat?’. There are a few things that you would have to consider.

To heat up 1.500 square feet, you are going to need between 45.000 and 90.000 BTUs. The exact number depends on the climate zone you live in, the insulation, the height of your ceilings, and even the material the building is made out of.

What do these BTUs even mean? What formulas can you use to calculate the number of BTUs needed and what factors you should pay extra attention to?

Below we tried to answer all the questions that you might have.

What Are BTUs?

First things first, what does this mysterious acronym actually mean?

BTUs stand for British Thermal Units. Don’t worry, even though the term literally has ‘British’ in it, BTUs are used in the United States as well.

Basically, the British thermal unit refers to the amount of energy needed to increase the temperature of a single pound of water by one degree Fahrenheit at sea level.

When it comes to cooling or heating systems, BTUs are used to express how much heat the unit can add or remove to the room per hour.

In a nutshell, the higher the number, the more powerful your heating or cooling unit is.

Fun fact: total US primary energy consumption per person was around 282 million BTUs in 2020.

Why a Higher Number of BTUs Is Not Always a Good Idea?

You might now think that it is worth going for a unit with the highest possible BTU level. But such a device is not the right answer for everyone.

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If your room is too small for such a powerful air conditioner or heater, the unit would end up heating or cooling the room too fast. This means that the system will be turning on and off too often.

In such a case, your energy bills are going to skyrocket and the actual system is going to wear out much faster.

So, in this particular case, going big is not always beneficial. 

Read: What Size Heat Pump Do I Need?

How Many BTUs Do I Need to Heat My House?

Fortunately, you can easily find quite a few convenient calculators online that can count how many BTUs you are going to need.

However, you can always choose to do the math yourself. For that, you would have to take the following factors into consideration:

  • The total square footage of your house

You need to measure the place that you will be heating. Whether that’s going to be a small room or a whole building – it’s all up to you.

  • The climate zone you live in

The US is divided into seven climate zones. Heating a house in Florida would require far less BTUs than increasing the temperature in a house located in Illinois.

You’ll find Miami, for example, in Climate Zone 2. This region typically requires around 35 BTUs of heat per square foot.

Chicago is located in Climate Zone 5. Houses in this region will require approximately 50 BTU of heat, and so on.

Climate ZoneBTU per Square Foot
Zones 1 and 2 (hot)30-35
Zone 335-40
Zone 445
Zone 550
Zone 655
Zone 7 (close to the Canadian border, very cold)60

Tip: if you are on the border between the climate zones, choose the zone that’s colder.

To make things a bit easier for you, let’s find the solutions to the examples below.

Read: What Is Heat Pump? Everything You Need To Know

How many BTUs do I need to heat 1500 square feet?

Answer: between 45.000 and 90.000 BTUs (simply multiply the recommended number of BTU per square foot and the size of the room/house).

The exact number would depend on the climate zone you live in. However, the majority of people live somewhere in between zones 1 and 7, so, in a lot of cases, you are going to need about 67.500 BTUs.

What size room will a 5000 BTU heater heat?

Answer: a room that’s between 83.33 and 166.66 square feet (we found that by dividing the size of the room by the recommended BTU per square foot).

Once again, the number is going to depend on the climate zone where the room is located.

If you live in an area with a cold climate, you are going to need a heater with the same BTU level, but for a much smaller room.

How many BTU do I need for a 12×12 room?

Answer: if the room is 12 feet long and 12 feet wide, then the square footage is 144. That means that you are going to need between 4.320 and 8.640 BTUs. 

A standard space heater provides around 5.100 BTUs, so that might be the right option for such a room, if it’s located in a zone with a mild climate.

What Factors Impact the Heating Needs?

All the formulas mentioned above and the numbers that you’ll find in the tables below can be used as a benchmark. 

Do bear in mind that it is extremely hard to determine the precise number of BTUs required to heat or cool a room or house as there are way too many factors that you have to consider.

·      Climate

We already know that the climate zone affects your heating needs. But weather can be unpredictable.

Some years might be warmer than the others. Moreover, the humidity levels determine how we perceive the outdoor and indoor temperature.

It is practically impossible to take all these nuances into consideration, but the climate zones and the corresponding BTU requirements are still a great place to start.

·      Square and cubic footage

A lot of BTU calculators ask you to provide only the square footage of your room or house. But the cubic footage matters as well.

The higher the ceilings, the more powerful the unit has to be.

Here is another formula that you can use to calculate how many BTUs you are going to need to heat up a room:

Desired temperature change x cubic (!) feet of space x 0.133 = British thermal units needed (per hour)

To find the desired temperature change simply find the difference between the outdoor and indoor temperatures.

Tip: if you don’t know the square and cubic footage of your house, you might find the necessary information on a house drawing. Or you can always measure the rectangles and the height of the ceilings in your house, multiply them, and then add the totals.

·      Quality and type of building material

It might come as a surprise, but the age of your house, as well as the type of building material, the location of the windows, and the layout of the rooms will affect how much heating and cooling the house needs.

·      Insulation

Two things matter – how well your house is sealed and how thick your insulation is.

Ideally, your place shouldn’t have any gaps around the doors and windows, and all the places where the pipes and ducts leave the house have to be well-sealed.

When it comes to the thickness of your insulation, there are certain levels recommended for each climate zone.

Taking care of these issues will help you save a fortune on energy bills. Moreover, you might be able to go for a less powerful unit, if your house is fully insulated. 

  • Sun exposure

Even the trees around your house should be considered when picking the right HVAC unit. 

The more tall trees there are, the more shade your house receives. That means that the rooms in your house might never get too hot.

However, do bear in mind that the level of sun exposure is a bit different in every climate zone. For example a ‘very sunny’ day in the extreme south might feel completely different to a ‘very sunny’ day in an area close to the Canadian border.

Read: Why Auxiliary Heat On But No Heat?

Heating BTUs Tables 

The tables below are provided for reference only.

But you can certainly use them as a starting point when picking a new heating and cooling unit.

Square FootagePoor InsulationModerate InsulationProper Insulation
200 9.000 BTU6.000 BTU4.000 BTU
40018.000 BTU12.000 BTU8.000 BTU
80036.000 BTU24.000 BTU16.000 BTU
100045.000 BTU30.000 BTU20.000 BTU
Square FootageVery Cold ClimateMild ClimateVery Hot Climate
50030.000 BTU22.500 BTU15.000 BTU
100060.000 BTU45.000 BTU30.000 BTU
150090.000 BTU67.500 BTU45.000 BTU
2000120.000 BTU90.000 BTU60.000 BTU

To Sum Up

The two most important factors that you have to take into consideration when choosing the BTU level of your heating or cooling unit are the square footage of the house and the climate zone you live in.

If you want to go the extra mile, you can pay attention to the sun exposure and the insulation of your building as well.

In any case, it is incredibly important to try and choose a unit with the most suitable BTU level as the efficiency of the whole system is going to depend on that.