What is a Heating Load?

Mary McMahon
Mary McMahon

A heating load is a measurement of how much heat is required per hour to heat a given space, and to maintain a desired temperature. A number of factors go into the calculation of this measurement, and there are several software programs which allow people to input variables for the software to run through a calculation which will determine heating load. People can also do the math by hand, a skill which is often taught to people who install heating systems, contractors, engineers, and people in similar industries.

A radiator, a common means of heating.
A radiator, a common means of heating.

Heating load is usually expressed in British Thermal Units (BTUs) per hour, using a familiar unit of energy to ensure that people instantly understand what the measurement means. It is calculated before installing a heating and cooling system, to determine which size would be most appropriate, and it is also calculated during the design of a structure, for the purpose of implementing changes which will make the structure more efficient.

Obviously, the size of a space is a key factor in the heating load. It takes less energy to heat a smaller space than it does a large one. The layout of the space can also play a role, with factors like ceiling height, number of rooms in a structure, and so forth influencing the load. The potential for heat loss through doors, windows, and other openings is another area of concern, as is the energy required to heat air from the outside, if it is being used for ventilation. Things like insulation can decrease the heating load by reducing heat loss.

Understanding the heating load is important. When installing a heater, if the heater is too small for the space, it will struggle to heat it, and use a lot of energy in the process. On the other hand, if the heater is too large for the space, it will not operate efficiently, generating wasted energy which adds to the lifetime cost associated with the structure. Heating load can also be an important factor when evaluating sustainability or thinking about changes which could be made to make a structure more sustainable.

When a heating and cooling consultant arrives at a structure to assess the needs, measurements of the space will be taken and a number of observations will be noted down. This information will be used to calculate the heating requirements so that an appropriate recommendation for a system can be made.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@David09 - I think that those programs are good if you want something full featured. But if you just need a quick snapshot of your load requirements you can find free heat load calculator applications online.

You just enter in the room dimensions, number of walls, and information about insulation and types of windows. Instantly you’ll get your heat load calcs and have a good idea of how much heating and cooling you'll need for your house.


@NathanG - I’ve used those units as well and I agree that they work.

If you need a contractor to do any heating and cooling, however, you’ll eventually need to calculate heating and cooling load at some point if you want to compare your estimates with those of the contractors.

The good news is that you don’t need to do these calculations yourself. There are a number of heat load software programs you can get off the Internet which will make the job easier.

They will let you build projects where you tell the software the rooms you will be heating, the size and location of the walls, floors, etc., and it will calculate the heat load or cooling load, whatever the case may be.

I’d recommend that you look into these tools if you ever need contracting work done, and want a ballpark figure of what your load requirements should be.


At night during the winter I sometimes use a small space heater in my room for heating the room. It’s a practical and effective heating and air solution for one room; I then don’t have to heat the entire house and I can save money.

I don’t know how much heating load is needed for the room, but the space heater seems to do the job quite well. Energy bills in the winter can be really expensive if you try to heat the whole house and you don’t use a fireplace.

The space heater is an inexpensive unit and has two settings so that I can adjust it as needed.

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