Is the size of my air conditioner right for my home?

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March 29, 2016
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April 5, 2016

Is the size of my air conditioner right for my home?

Whether you are buying an air conditioner for the first time or you are replacing an old unit, once of the most important features is the size of the unit. As a matter of fact, a disproportionate A/C (both bigger and smaller) will not only have a negative effect in the cooling of your home: it will drive your electricity bill up the wall. So if you suspect you’re A/C isn’t the proper size, you may want to think about replacing it even if it work fine.

So what sizes are there?

The first question to ask is: what sizes do air conditioners come in?What you need to know is that A/C use “tons” as measure, but they are not the regular tons we use for measuring weight. What this one actually means is the A/C’s ability to cool its surroundings.

If we get technical, a ton is defined as the A/C’s ability to cool 12,000 BTUs, which stands for British Thermal Unit (fun fact: the British don’t use this unit at all) and means the energy needed to heat or cool a pound of water by 1°Fahrenheit per hour. For residential places, air conditioners come from 1-ton to 5-ton. So if 1-ton cools 12,000 BTUs, 2-ton would be able to cool 24,000, 3-ton 36,000 BTUs, and so on.  

Bigger is not necessarily better

An important myth to debunk here is that getting a bigger air conditioner than your house needs would work better, just because. This is untrue. Actually, getting the wrong size would only beproblematic one way or another, unless you have an A/C from the 1980’s. (Hint: if you do, you should be replacing anyway).

Air conditioners run in cycles. They work slowly (unlike old air conditions, that lowered temperature very rapidly) but steadily, keeping your home nice and cool and running the cycles efficiently enough that your electrical bill will benefit from it.

We already stated what the consequence for too big or too small A/Cs is, but not the reason for it. When you have a too big air conditioner, it will cool your house rapidly, but as it senses that the job is done, it will shut-off soon after and not complete the cycle is was designed for. When the heat sneaks back in, it will turn on again, but this turning on-and-off problem will show itself later in your bill.

If the A/C is too small, however, it will never turn off. It will never reach the temperature it is intended to, therefore it will keep running in an attempt to catch up. Unless the A/C is unreasonably small in comparison to your house the cool will probably be good enough, but again, the constant running of the system will be reflected on your bill.

In short, bigger or smaller than necessary air conditioners would still do the job, but they won’t do it efficiently.

I still don’t know what size I should get

Sorry about that. But truthfully, this is one of the A/C issues you definitely have to leave to a licensed HVAC professional. It is not only about the size of the house, there are many factors that influence the actual heating and cooling loads in it. For example, your contractor will need to determine insulation R-values, analyze how the shapes of your windows affect all of it, air-flow orientation, infiltration rate, ducts state and leakage, among others