Heating and Cooling Load Calculations

If you aren’t familiar with the HVAC industry, this topic probably makes no sense to you. Well, I hope that by then end of this post you will understand what a Heating and Cooling Load Calculation is and why it is important.

In its most simple terms a Heating and Cooling Load Calculation is a process of determining how much heat a home gains in the summer and loses in the winter. This information is then used to correctly size the heating and air conditioning equipment for the home. Unfortunately, this type of calculation is like a foreign language to many in the HVAC industry.

One of the most common questions in our industry is “When do you need to do a Load Calculation?” And depending on who you ask, the answer will range from “every time” to “only if the customer asks”. Since I like to take a logical approach to things, I will answer the question this way, “It depends on the situation and what you will be doing.” So, what does that mean?

In theory you would do a complete Heating and Cooling Load Calculation for every job, but that just isn’t practical. It isn’t practical for several reasons. The customer may not have the time available. You may only be replacing one part of an existing system that has performed to the customer’s satisfaction until it broke. You may be replacing a complete system, and the previous system met the customer’s needs without problems.

Okay, so when is it imperative that you do a Heating and Cooling Load Calculation? Well, there are a number of such situations. If the customer is requesting to increase the size of the equipment. If the customer is installing a geothermal system. If the customer has complained of problems maintaining desired temperatures and the current system appears to be sized correctly. If the customer has made significant modifications to their home to improve its energy efficiency – such as insulated windows or extra insulation.

Why is it important to do a Heating and Cooling Load Calculation? The most important reason is to assure that the new system will meet the heating and cooling needs of the home. At the same time, a system that is too large will not run long enough to provide proper filtration, humidity control and air movement for even temperatures. It also costs money to install new equipment, and customers should only be asked to invest in a system large enough to meet their needs, but not too large – thus spending extra money to purchase larger equipment.

So, what is involved in a Heating and Cooling Load Calculation? To conduct a proper Load Calculation the entire floorplan of the home must be mapped and measured. This provides the exact amount of square footage to be heated and cooled. Additionally, all of the windows and doors must be measured, and their type of construction must be noted. The type and amount of wall and roof insulation is recorded, as well as the thickness of the outside walls and the exterior construction materials. Roofing materials and attic ventilation is also noted. Flooring and foundation type also plays a role in the calculation. The direction the home faces and a number of other factors are also recorded.

All of this information is then used to recreate the home, usually in a software program, where the actual Heating and Cooling Load Calculation is performed. Once all of the information has been entered, the exact heating and cooling needs of the home are available. This information is used to determine the proper equipment size for the home. This information can also be used to provide estimated annually utility costs for heating and cooling.

With all of this said, I think you can see why so many people in the HVAC industry don’t, or won’t, take the time to perform a Load Calculation. At the same time, you can also see why some people just don’t have the time. The good news is that an experienced professional can obtain all of the necessary information fairly quickly, and they can return at another convenient time to present the results, if a Load Calculation is needed.

I hope I haven’t confused you, too much with this information. If you have any additional questions, I would be glad to help. Just drop me an e-mail, or give me a call.

THANKS!