When you’re deciding on installing a new central air conditioner the first question that comes to your mind is “how do I escape this heat?” Right now we are in the middle of another heat wave in Toronto, and the questions that we get asked most often at EcoLife at this time of year always involve keeping your home cool. Getting a new AC will cover that, but when deciding on what size of unit to get there are several technical aspects to consider. The size of the AC is one of the most important, but these questions can get pretty technical if you don’t have prior HVAC knowledge (keep in mind that size and type are very different things). So that you know what to ask for, here’s a quick guide of how to determine what size central air conditioner you need for your home.

How A/C Size is Measured

Central air conditioners come in a variety of sizes and are measured in “tons”. Contrary to what you might think, tonnage is not based on its weight but on the air conditioner’s ability to cool. 1 ton represents the cooling of 12,000 BTUs (British Thermal Units) per hour. BTUs measure the amount of energy required to heat or cool one pound of water by one degree Fahrenheit. That sounds complicated, but in other words, an air conditioner of 1 ton would be able to cool 12,000 pounds of water by one degree every hour. Plain and simple.

The tonnage of your home’s AC will usually range from 1 ton to 5 tons and increase in half-ton increments. If your home needs more cooling than 5 tons, HVAC professionals usually recommend installing several units in tandem because anything over 5 tons is considered a commercial HVAC unit. The reason for installing two systems would be that if one unit completely fails, another one will always still be running as back-up.

Getting the Right Size

It is very important to install the right size A/C in your home for a variety of reasons as units of the wrong size will cause energy bills to skyrocket and can compromise your comfort at home. Modern central air conditioners, on the other hand, function on high efficiency and run in cycles which slowly and steadily cool your home.

Air conditioners that are too big will turn on quickly, cool your home rapidly and then shut off. This will interrupt the cooling cycle that your unit was designed for and force your unit to turn on and off more rapidly, causing uneven temperature spikes. This constant on-off cycle will also defeat the purpose of its high-efficiency design and cause your electricity bill to skyrocket. Units that are too small on the other hand will run constantly to compensate for having too large a space to cool and will also cause your energy bill to increase.

A properly sized central air conditioning system will keep your house comfortable and run according to energy efficient cooling cycles. What this means is that a properly sized unit will use energy more effectively and will not only lower your energy bills, but keep your home at a more consistent temperature.

How To Get a Ballpark Estimate

Now that you know what sizes your AC can come in and why the right fit is important, let’s go over how to get a rough estimate of what size is right for your home. The equation goes as follows:

((House square footage x 25, ÷ 12,000) – 0.5) = required tons.

Here’s an example on a 1,500 square foot home:

  1. 1,500 X 25 = 37,500
  2. 37,500 / 12,000 = 3.1
  3. 1 – 0.5 = 2.6

So, for a 1,500 square foot house you would need a 2.5 or a 3-ton sized central air conditioning unit.

Now you’ve got an explanation as to why it’s important to get the right size AC, how they are measured and how to calculate how many tonnes you will need. Of course, there are many other factors in your home that will affect the size of air conditioner that you need such as the height of your ceilings, the type/ thickness of insulation etc. It is still important to trust an HVAC professional when installing the right A/C unit, but now you will know what to ask for!