How Do I Know What Size Ductless System I Need (Video)

In this video, Mike Cappuccio from Jones Services talks about how to determine which size of ductless system you need. He explains the factors that affect system capacity and talks about why you cannot just consider square footage.

Hello, I’m Mike Cappuccio from Jones Services, and today I’m here to talk to you about, “How do I know what size ductless system I need for my home?” This is a very common question that I get asked a lot, “What size system do I put in my home? My room is 20 by 20. It’s 400 square feet. What size air conditioner do I put in there?”

Well, there’s a lot of factors that go into that space or even that home. One of the biggest problems I see when I go out to homes is that the air conditioning system is too big. People buy too big of an air conditioning system, and they think bigger is better. Well, that is not the case with air conditioning. the bigger-is-better mentality is definitely not a good thing.

With clients who want a ductless system, we come out to the home, we sit down, we have a conversation, and we look at everything. For example, say you’ve done a lot of improvements on your home, such as, “I’ve put new windows in my home that were leaky. I’ve replaced those windows that don’t leak. They have a high tolerance to sunlight outside. The sun doesn’t come in as strong anymore. I might have even put blinds on my windows, that even reduces an air conditioning load as well.”

The other thing is insulation. What type of weatherization have you done to your home? Now, I want you to think of those few things that I just mentioned and think of your home when you made those changes and your home before you did those changes. So, if you replaced the windows and reduced your heating load in your home.

Now, you’re not using as much energy to heat your home. Well, it’s the same thing with cooling now. If you’re having a conversation with a comfort consultant, and we’re out at your home, they need to know these improvements that have been made in the home. Now, we go back to the home, and we run a quick manual J load calculation on the home, and we determine what size air conditioning system is good for the home because bigger is not better.

When an air conditioning system is too big, it will cool the home. It’ll definitely cool the home. It’ll run and bring the temperature right down to where it needs to be, to 72 degrees. Let’s say, that’s where you had the thermostat set. And, it ran for five minutes, brought the room down to 72 degrees and then, it shuts off. Well, 72 is good, but you could have 72 with 80% relative humidity in the room. So, what do you end up with, with an air conditioning system that’s too big for a room. You end up with cold, clammy rooms, very humid and cold. It’s almost like a very damp day in a walk-in cooler, I would say at that point. It’s very cold and clammy.

What happens when we have a lot of moisture inside our homes? Now, we start to develop mold inside the home because the air conditioning system is not removing the humidity that’s in the space. Here’s an example, when you look at your car and your car’s running in your driveway, and it’s a 90 degree day, and you see all that water on the ground. Well, that’s the humidity that’s being removed from the space inside of your car, keeping your car comfortable, same thing with your home. You want to get that water that’s inside the air in the home, outside.

The way you do that is by letting your air conditioning system run 60, 70, 80% of the time. If it only runs 10% of the time and shuts off, it’s never going to remove that humidity from the home, so bigger is not better with air conditioning.

You need to make sure that the system is sized properly by a professional. How does a professional do that? We do what’s called a manual J load calculation on your home. It’s software and when we’re putting the parameters of your home into the software, we’re looking at the improvements that have been done to your home, insulation, windows, air ceiling, blinds. We’re also looking at which side the sun hits your home. Is it a northerly exposure? Is it a southerly exposure? Is it west, east? When does the sun shine into a big window? Is it in the afternoon, in the back of the home? These are all factors that play into your air conditioning system when we come out, and we size it in the home.

A lot of guys I know… I have been in the industry for a long time, I’ve been doing this for almost 40 years now. They size by rule of thumb, 400 square feet requires 12,000 BTUs. Well, you get into some homes today that are well insulated, and when you run your load calculation and you look at 400 square feet, it might be 8 BTUs a square foot, depending on how well this house is insulated because there’s no heat impact. The warm air and the cold air isn’t leaking outside from the heating and, or the cooling.

So, you’ve got to know from a weatherization standpoint or even what year your house was built. You look at a house built in the early 1900s with no insulation, and you look at a house that’s built in 2020, that’s obviously a lot different.

Air conditioning heating loads are a lot different today in newer homes than they were in older homes. You really can’t use a rule of thumb theory on just sizing air conditioning. Just some of the problems that can happen when you do that… you’ve got to really have a professional come out and look at this when you’re doing this, just keep that in mind when sizing and heating and cooling an air conditioning systems for your home.