May. 02, 2018
If you’re searching for this answer online, you’ll likely come across generic AC-sizing suggestions, like this:
- 1,000–1,200 sq/ft= 21,000 BTUs
- 1,200–1,400 sq/ft= 23,000 BTUs
- 1,400–1,500 sq/ft= 24,000 BTUs
- 1,500–2,000 sq/ft= 30,000 BTUs
- 2,000–2,500 sq/ft= 34,000 BTUs
- 2,500–3,000+ sq/ft= 42,000–60,000 BTUs
You see, sizing an AC using vague rule-of-thumbs (i.e. only looking at square footage) is like purchasing new clothes for someone—knowing only their age/gender: you’ll likely end up with the wrong size and lots of money wasted.
So how do you determine the AC size you need? By having a qualified professional perform a “cooling load calculation”.
In this article, we’ll explain:
Just contact us.
Air conditioners are sized according to much heat they can remove from your home in an hour—this is measured in BTUs (British Thermal Unit—a measurement of heat).
How are air conditioners sized in the first place?
Typical New Jersey homes need air conditioners that have BTU outputs ranging from 18,000 to 60,000.
Note: For context, one BTU approximately equals the amount of energy needed to heat 1 pound of water by 1 degree—or roughly the same amount of heat produced by burning one match.
Now, don’t get confused if some resources/sites size ACs by “tonnage” instead of “BTU output.” AC tonnage is simply another way to tell you the unit’s BTU output.
For example, one AC “ton” is equal to 12,000 BTUs.
Fun fact: 12,000 BTUs is the amount of heat required to completely melt one ton of ice (hence the use of “tons” when it comes to AC sizing).
To help you quickly determine an AC’s tonnage or BTU output, use the information below:
- 1 ton = 12,000 BTUs
- 1.5 tons = 18,000 BTUs
- 2 tons = 24,000 BTUs
- 2.5 tons = 30,000 BTUs
- 3 tons = 36,000 BTUs
- 3.5 tons = 42,000 BTUs
- 4 tons = 48,000 BTUs
- 4.5 tons = 54,000 BTUs
- 5 tons = 60,000 BTUs
And that’s where a professional “cooling load calculation” comes into play.
Let’s take a closer look at what this calculation entails…
When a HVAC contractor determines the AC size you need, they should never give you an answer until they’ve performed a “cooling load calculation”.
What is a “cooling load calculation” and why do I need one?
A cooling load calculation determines how much heat needs to be removed from your home in an hour in order to maintain a constant comfortable temperature.
In other words, a cooling load calculation tells you the BTU output you need from an AC.
When done properly, a cooling load calculation takes into account over 10 different factors, including:
- Your geographical location (New Jersey homes shouldn’t use the same sizing guidelines as Florida homes, for example)
- The orientation of your home (is it facing Westward, Eastward, etc.)
- How many windows your home has (and what kind of windows)
- How many doors your home has
- Whether your home has carpet or wood flooring
- How many people live in the home
- Your home’s insulation levels
- Whether your ductwork is located inside or outside
- And much more…
But of course, this brings up another important question: Is it really that big of a deal to have an air conditioner that’s over/undersized?
That’s a fair question—let’s explore it more in depth below…
Yes—when it comes to air conditioners, size matters.
Does proper AC size really matter?
Let’s look at why both oversized and undersized air conditioners cause problems.
...it cools your home too quickly.
When an AC is oversized…
That may sound weird to the average homeowner but, yes, cooling your home too quickly can be a bad thing. That’s because the longer an air conditioner runs, the more moisture it can absorb from your home’s air. But if your AC comes on, quickly cools off your home then shuts off, it doesn’t dehumidify your home well. Which is a New Jersey homeowner’s worst nightmare, right?
An oversized AC also consumes a lot more energy. That’s because an air conditioner actually eats up more energy as it starts up versus when it’s running steadily. And, because an oversized AC quickly heats your home then shuts off, its “start up” time is a greater fraction of its overall runtime (i.e. much higher energy bills). Plus, an AC that’s constantly turning ON/OFF (called “short cycling”) puts strain on internal motors/components, resulting in frequent repairs and a lowered lifespan.
...it runs non-stop and still struggles to keep your comfortable.
When an AC is undersized…
Even though undersizing is less common than oversizing, undersized ACs still cause just as many problems. You see, if an air conditioner is undersized, that simply means the unit can’t remove heat as fast as it’s coming into your home. This means your AC will have very long run times—it may even run non-stop—which means very high energy bills.
But even when they run non-stop, undersized ACs still can’t keep you comfortable. Plus, they quickly become overworked, which means more repairs and (you guessed it) lowered lifespans.
Just contact us.
Have questions? Need a cooling load calculation?
We can help with all your air conditioning needs. We also offer FREE cooling load calculations when you contact us for an AC install estimate.