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.
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.