Air Conditioning System Sizing

Size does matter, and bigger isn’t better when it comes an AC’s cooling capacity.

You’d think that given your AC’s purpose in life is to remove heat from your home, having a bigger AC should be better, as it can remove more heat, and that’s what it’s there to do, but that actually isn’t the case.  An AC that’s too big will cool the air in the home too quickly, and yes that is a thing.  The notion behind cooling a home with an AC is that we’re not so much trying to cool the air itself, rather we’re trying to use the air as a delivery vehicle to remove heat from the dense material in the home; the walls, floors, ceiling, furniture, etcetera.  The air can’t hold much heat, the dense material in the home can, so the air is fairly quick and easy to cool, and the rest of the home is not, which is precisely why an oversized AC is a bad thing.

An oversized AC will cool the air too rapidly, lowering the air temperature quickly, satisfying the thermostat before the heat in the dense material within the home has a chance to get soaked up by the cool air in the home, then once the AC shuts off, the dense material in the home will heat the air back up nearly as quickly as the AC cooled it, the thermostat brings the AC back on, and the cycle continues.  This causes the AC to turn on and off more frequently than it was designed to, and is referred to as “short-cycling”.  As all mechanical systems and their components are designed for X many actions, X many “opens and closes” of their switches, X many “ons and offs” of their motors, short-cycling wears out furnace components much quicker than they were designed to. Short-cycling also causes a wave-like rise and fall of household temperatures, with the temperature falling rapidly when the AC is on, and raising rapidly when it’s off.

An oversized AC will also be louder, as it’s trying to operate in pressures outside of its designed parameters, will cost more to purchase and operate, as there’s more to, and in some situations, may be perpetually problematic for its owner, with it unable to run for long before it freezes solid, leaving the home without any cooling whatsoever until it’s thawed out.  An AC system needs the heat in the home’s air to keep its operating pressures within its design parameters, and without sufficient heat in the home for it to remove, its pressures will drop which brings its temperature below freezing, and then all the moisture that precipitates out of the home’s air onto the indoor portion of the AC system, the portion of the AC system that’s actually removing heat from the home, freezes to it quickly turning it into a solid cube of ice sitting on top of your furnace, leaving the home without any cooling, and setting the stage for that approximately 2’ cube of ice to eventually melt, with a lot of that melt water dropping into the furnace, expediting the degradation of many furnace components, sometimes destroying them outright.

Bigger isn’t better when it comes to air conditioning systems.