What is a Load Calculation? And Why is this Number so Important?

November 13, 2016 Todd Hoffman

Think of two scenarios. In the first scenario, imagine a room lined with thick metal on every surface, then with wood, then with thick blankets and more wood. This room has no windows or doors or any openings. If an AC were to blow cold air into this room until a perfect temperature were achieved, the cold temperature would last a long time because so little cold air would be able to escape and because so little air would be able to infiltrate.


A homes exfiltration and infiltration rate are important. When your home’s HVAC system is punching air out of the vents, it is also trying to create a positive pressure situation in your house by shoving out all the air in your home and ‘pushing’ and exerting it out through the cracks in windows walls, doors etc. No home is truly sealed, as this would create too much moisture and need very expensive systems to perfectly balance the humidity (think BioTech labs, etc.). When we talk about air in the room being pushed out or sucked in, we are talking about Air Changes. A home will need certain Air Changes per hour in order to adequately cycle the air. You cannot be left with just the same air in the room; it must be exchanged.


In a second scenario, imagine going camping during hot weather and bringing an AC unit with you. You set up your tent and notice a few holes in the tent. But you set up the air conditioning unit anyway. Though the AC runs and runs, your tent barely gets cold. Cold air is escaping through the holes in your tents and leaking out through the thin tent material. Within minutes of turning off the AC unit, your tent is hot again. This would be the equivalent to a house that has too many air leaks. If those items are not going to be fixed, then the system will need to be sized perfectly so that you don’t have short cycles and equipment failure.

Each of these scenarios represent two different load calculations. Now, if you really wanted to get a cold tent, we would need to patch up the holes, possibly insulate the tent better, and then figure out what size system would be able to keep your tent cold. With a strong enough system and better insulation, we could even get a tent to stay cold.


This is the simplest way to understand load calculations.


When we determine a load calculation on your home, we will take into account the size of your home, the openings, the insulation, and other factors. Based on this calculation, we can determine what needs to be done to get you the best system for your situation. We can also make recommendations that will make your current system be able to perform the way you need it to perform, whether you need AC or Heat.


Call Texas Discount Air @ 682-214-HVAC(4822) to see if you have Sick Building syndrome, adequate Air Changes per hour, and all the other items we just spoke about.