Unlike central air conditioners, which are sized to cool an entire home, ductless ACs are sized to cool only one room/area.
But here's the deal: Without a technician looking at the room you want to cool, it's impossible to know exactly which size ductless mini split system you need.
You see, a professional need to perform a load calculation to determine mini split AC size. A load calculation takes into account many factors like:
But you still probably have lots of questions about ductless mini split size.
In this article, we'll explain:
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Ductless units are sized according to how much heat they can remove from a room in an hour. This amount of heat is measured in British Thermal Units (BTUs). One BTU is roughly equivalent to the amount of heat produced by burning through one match.
So, you’ll often see ductless units referred to by their BTU output (i.e., a 15,000 BTU output ductless unit). Ductless BTU outputs can range anywhere from 9,000 to 48,000 BTU.
Now, before we talk about how you can determine the BTU output you need, let’s answer the question we get all the time from Denver homeowners: Is it really that bad if I get a unit that’s too big or too small?
Yes. An undersized or oversized ductless mini split means lower comfort and lots of money wasted.
...will run non-stop trying to cool a room that’s too big for the unit to handle.
And a unit that runs non-stop will:
...will cool the room quickly then shut off.
This quick ON/OFF pattern (called short cycling) will cause:
So now that we know correct size matters, let’s look at how a professional load calculation works and how it ensures that you get the precise ductless size you need.
To determine the ductless AC size you need, a professional should always perform a load calculation instead of only looking at the square footage of your room.
During this load calculation, a professional will measure the amount of heat that enters a room based on factors like:
This precise calculation allows a professional to determine the exact BTU output you need from your ductless mini split—no more, no less.
Most quality professionals will include a load calculation in the initial installation estimate.
That said, if you’re in the middle of choosing a professional to install your ductless unit, stay away from any tech that sizes your ductless unit over the phone (using only square footage). Only looking at square footage often results in the wrong ductless AC size.
Let’s say that you have a 900-square-foot room.
If you were to only use square footage to size your ductless unit, you’d end up with a unit that has a 16,000 to 17,000 BTU output, right?
Now let’s take a closer look at that 900-square-foot room. Let’s say that the ceilings are 10 feet high and about 90% of the east-facing wall is covered in poorly insulated windows.
After taking into account those additional factors, a professional would likely increase the needed BTU-output by about 50%, which leaves you with a unit that has a 24,000 to 25,000 BTU output.
That’s a big difference.
We offer FREE load calculations and upfront, honest pricing.
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