Load Calculation, A Guide To Proper Equipment Sizing
A load calculation is the process of determining the proper size of a furnace
and/or air conditioner for a home.
In the early days of the industry, hvac companies made an educated guess to
determine the heat gain and loss for the home. The guess was based almost exclusively on the square
footage of the home and was not even close to being accurate. The main concern of the hvac company was
to make sure the unit was big enough so they would not be sued. Therefore, they usually installed a unit
that was much bigger than required.
Later, an organization called the Air Conditioning Contractors Of America
(ACCA) was formed. They developed standards and a method to more accurately find the home's heat gain
and loss. It involved many complex mathematical equations and required a lot of time to perform.
Therefore, most contractors did not use the system.
With the age of computers, this process has become even more accurate and
requires less time. The computer software takes into account every detail of the construction of the
home and how it affects the heat gain and loss. The software is pretty expensive and therefore many
contractors still guess and hope for the best.
One of the basic laws of thermodynamics is that heat moves from a warmer area
to a colder area. When it is colder outside than inside the home, heat travels to the outside. The heat
that travels to the outside is called heat loss. At the same time, heat is added to the home constantly
by things such as appliances, the sun shining in a window, or people. If the heat being added by those
sources is less than the heat escaping, then heat from another source must be added to maintain a
desired temperature. The amount of heat that must be added is called the heat load.
When it is hotter outside than inside, the heat from the outside travels to the
inside of the home. That heat plus the heat from the internal sources mentioned above is referred to as
the homes heat gain. To maintain a given temperature, this heat that is gained must be removed. The
amount that must be removed is called the cooling load.
A load calculation is the method used to find these heating and cooling