This BTU calculator determines the necessary heating or cooling capacity calculated in BTUs/h so you can choose the right radiator or air conditioning unit. Read more on this subject below the form and even how to determine the amount of energy you need to heat or cool your house.

Width: *
Length: *
Height: *
Room type: *
Other factors:
Width: *
Length: *
Is there a kitchen in the space? *
How many persons use the room? *
Other factors:

How does this BTU calculator work?

This home tool allows you to determine the necessary heating or cooling capacity calculated in BTUs/h so you can know exactly what radiator or air conditioning unit power works for your house. Calculating your house's heating requirements has never been easier.

The BTU calculator is a quick way to determine the heating or cooling requirement for a specific space and could be considered guidance in choosing the right equipment. In order to understand how the form really works we need to explain the definition of BTU and also how you could calculate it on your own, given the dimensions of the room you have.

What is a BTU?

A British Thermal Unit (BTU) is the measure of energy required to heat 1 pound of water 1 degree Fahrenheit. One is roughly equal to 1,055 Joules. 1BTU/hour is equal to 0.293 watt. This is the standard measurement of heat output needed to heat any structure, therefore can measure radiator power.

The amount of BTUs required depends on many variables including the dimensions of the room or space, the destination of that space, construction variables such as degree of insulation and even on climate factors. A simple use of the above tool can help you know the energy necessary for heating or cooling your home. As it already adjusts the basic BTU calculation depending on your answers regarding the factors influencing the efficiency of the system in question.

The capacity of furnaces and air conditioners is given in BTUs per hour. You need to establish the correct number of units for your house needed to either heat or cool it. The methods differ and are described below.

How many BTUs are needed to heat a room?

The BTU requirement will be for the whole room, so you need to calculate the total amount of space the room covers. To do that you need to measure the length, width and height of the room so you can then calculate the cubic footage of each room by multiplying the length, width and height of the room. 

L * l * h = cubic footage

To get a basic estimate of the heating requirement you then multiply the cubic feet by 3, 4 or 5 depending on the destination of the room starting with 3 for kitchens and common rooms, 4 for bedrooms and children rooms and 5 for dining and living rooms. The BTU requirement will then be adjusted accordingly to other factors that can influence the heating of the room. Poor home insulation, the existence of large windows, rooms with many exterior walls will determine a higher requirement so increase your calculation by 10%-20%.

On the other hand, a new, well insulated house with double glazed windows, and south facing rooms will lower the BTU heating requirement so don't forget to lower your  calculation by 10%-20%.

But how is the required amount of units to heat a room calculated if you want to increase the temperature in that room with a certain amount of degrees? You can easily determine the requirement in this case by multiplying the cubic footage by 0.133 and by the desired temperature increase. This will give you the final number of BTUs that you need to increase the temperature in your room by the desired number of degrees.

How to calculate how many BTUs are needed to cool a room?

First we need to understand what cooling capacity means. The cooling capacity of an air conditioning unit is measurable by BTU/h and represents the ability of that unit to remove heat from a certain space. Knowing the exact cooling capacity for your space helps you choose an appropriate air conditioning unit.

The first step to calculate the total units needed for home cooling is to measure the length and width of the space. Then use the obtained square footage to determine the BTU requirement by consulting a specialized chart on cooling energy. Here is one below:

Between Approximate BTU/h
Square footage ~ Min Square footage ~ Max
100 150 5,000
150 250 6,000
250 300 7,000
300 350 8,000
350 400 9,000
400 450 10,000
450 550 12,000
550 700 14,000
700 1000 18,000
1,000 1,200 21,000
1,200 1,400 23,000
1,400 1,500 24,000
1,500 2,000 30,000
2,000 2,500 34,000

Once you have the basic value for your space adjust this value according to the existence of a kitchen in the place (you need to add 4,000 BTU in this case). The Chart value is calculated for a space shared by two people. For each extra person add an extra 600 BTUs. You should also reduce the BTU cooling requirement by 10% if the space to be cooled is heavily shaded or add 10% to it if the place is very sunny. Knowing the required units for cooling your space can help you choose the right air conditioning unit.

Example of a result

  • Heating tab:

-for a room with a length of 16ft, width of 13ft and height of 8ft used as a bedroom that is north facing and has French windows and good insulation. Result is “The BTU requirement for heating a room with the details you entered is of 7,987 BTU/h, this is approximately 2.341 kW.”

  • Cooling tab:

-for a room with a length of 14ft, width of 13ft used as a kitchen by 5 persons plus it is placed in a sunny space. The result is “The BTU requirement for cooling a room with the details you entered is of 12,980 BTU/h, this is approximately 3.804 kW.”

18 Mar, 2015