Stop Using Your AC To Dry The Basement or Crawl Space

Cold air can fool you. A basement can feel crisp at 60 degrees while humidity sneaks past 70% and turns prized gear into mold bait. We bring on Alex Hamilton from Aprilaire to demystify why HVAC systems are built to control temperature, not moisture, and how that gap leads to musty smells, surface mold, and ruined finishes in basements and crawl spaces.

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We start with the classic contractor mistake: finishing or encapsulating a space without adding a dehumidifier. Alex explains how added ductwork without resizing the system reduces coil contact time and causes short cycling, which means the AC removes less moisture even if the upstairs feels perfect. Then we dive into a real-world case of a stunning, brand-new basement with humidity near 80%—leather pockets and felt on the pool table blooming with mold—because the basement sat below the thermostat setpoint and the AC rarely ran.

From there, we break down how dedicated dehumidifiers prioritize relative humidity and dew point, measuring inlet and outlet conditions to condense water efficiently and reheat the air so comfort rises without overcooling. We cover ducted installs from a mechanical room, RH targets for healthy homes, and why sealed basements and crawl spaces need active drying year-round. You’ll learn how reducing moisture can help the AC run less, why the stack effect moves damp air through the whole house, and the simple metrics to watch so you never get blindsided by hidden humidity again.

If you care about indoor air quality, building durability, and true comfort, this conversation gives you the clear path: seal smart, dry proactively, and stop asking your AC to do a job it wasn’t designed to do. Subscribe, share this episode with a homeowner or contractor who needs it, and leave a review with your biggest humidity headache—we may tackle it next.

Chapters

• 0:00 Humidity Vs Temperature Basics
• 0:39 Introducing Alex From Aprilaire
• 1:08 The Basement Dehumidifier Gap
• 2:32 HVAC Sizing And Coil Surface
• 4:10 Encapsulation Without Drying Risks
• 6:15 The Moldy Pool Table Case
• 8:20 Why AC Won’t Dehumidify Basements

Transcript

SPEAKER_01: 0:00

The Dhumidifier is designed to control humidity. The HPEC system is designed to control temperature. You're listening to the Crawl Space Ninja Show where Healthy Homes begins from the ground up. I am Michael Church, the founder of Crawl Space Ninja, and your host today. And we've got a great show for you. Many years ago, when I got involved in doing crawl spaces and basement waterproofing, one of the biggest things that the HPC industry was trying to do is regulate humidity in crawl spaces and basements with HC equipment. And we found that was not a good plan and wound up causing a lot of mold problems. So I've got Alex Hamilton here with me from April Air, and we go over that with you so you understand if you're getting told to use your HC unit to regulate humidity. It's probably not a good idea, especially in that crawl space, but in other parts of your home as well, whether you have a finished or unfinished basement or even an attic. Also, make sure you check out our description of this video because we got some great information for you. Let's get started. Even in basements, I've even seen this. If you can touch a little bit on basements, I think this is one of the biggest overlooked things that basement waterproofing companies uh have is they will not install a dehumidifier when they uh when they waterproof a basement. And I think that's a huge mistake. And we've even had instances where you have you know the mechanical room, and you can install that uh that dehumidifier in the mechanical room and then duct it in a way to where you're blowing in and out of that mechanical room so it's not an eyesore in the middle of the basement. Tell us a little bit about that too, if you don't like.

SPEAKER_00: 1:40

Sure. So and just just over the last couple of years, I've I've run into that exact thing where you know they're they're going in, they're encapsulating everything looks really pretty. Like it looks, it looks efficient, but they're not adding a dehumidifier. And something that I think homeowners and contractors need to understand is if you're not an HVAC contractor, okay, and someone finishes a basement and then they add ducting to that, but not a larger air conditioning unit to the home, you're actually going to suffer in the fact that it's not gonna be able to return enough air to dehumidify it. So what happens is you need more coil space. That's that's essentially where we get into sizing issues and things of that nature. You need more coil surface area to remove that humidity. So to do that, the only thing you can do is add a larger air conditioning system, or the more efficient and more proactive way to do that would be to add a dehumidifier. So for those instances where it's not necessarily a finished basement, um, if you're leaving the space fully encapsulated without a dehumidifier, whether it be a basement, a crawl space, or anything like that, it's kind of like closing the doors and the windows on your car and not having the air conditioner on. You know, it's going to change the entire ecosystem inside that space. But you know, you you know, a lot of people will say, oh, we roll the window down, you get the fresh air and things of that nature. With the basement, when we encapsulate, we want sealed. With a crawl space, we want sealed. So the only way to introduce conditioned air into that space is with a dehumidifier. Um that is that's something that's heavily overlooked because with you know, stack effect and things of that nature, stack effect doesn't just affect crawl spaces, it's gonna affect the basement. Um and with most basements, you're gonna see a concrete floor, a block wall, uh, in some cases you'll see a dirt floor uh with a block wall. And when we're sealing that up, if we're not actually taking that humidity out, it's still gonna find a way to change that ecosystem as far as the humidity, the temperature, and things of that nature.

SPEAKER_01: 3:35

Well, and I want to just advance what you just said a little bit because I've personally had some experiences where you're talking about adding more coil, right? Uh I forget exactly how you phrase it, but that's a good way to say it. You're basically adding more coil surface by adding a dehumidifier to an HPEC system. But there's also a problem. I had a buddy, if I could tell a quick story, he's a he's a home builder and he built this beautiful home, finished basement, you know, just immaculate, right? I mean, uh it was it's the man cave, you know, there's a pool down there and a bar and all that kind of stuff. And he calls me up and he goes, Michael, I don't know what's going on. I got uh the homeowners got mold growing on their on their pool table. This house is less than a year old and they've got mold growing on it. So I, you know, he calls me up, I go over there, and uh, you know, the the thing that people don't understand is a lot of times a basement's temperature is lower than the set point of the AC. So, you know, I get over there and I'm in the house and it's immaculate. They've taken care of it, it's very nice. I open the basement door, and as soon as I open the door, I feel a chill as well as a humid air smack me in the face. And I kid around about when I tell this story, I could almost hear like monkeys screaming down there because it was so humid, right? Right. So, and and and so I walked down there and it was just ridiculous. It was almost 80% humidity. There was surface mold getting growing, and he had like the pool table, it had like the leather pockets, you know, that were really nice. That leather was growing mold, the felt was growing mold, all this other stuff. And the problem was is the step point or the temperature was so comfortable because of how well the basement was built that the AC never turned on to help dehumidify the basement, and that's where you need something like an A-layer dehumidifier, even if it comes on twice a year, you still need it, right? Could you could you kind of share that a little bit? It's not that it's it has to run constantly, it just needs to be there in case you need it as well.

SPEAKER_00: 5:42

Well, I think we get confused, like, you know, you can be you could have the temperature exactly where you want it, and we think that that's where comfortability lies is strictly temperature, and that's just not the case. Um with high humidity, obviously, if the air conditioner is going to run constantly in the summertime. I mean, we're in the southeast, I mean, we know how this works. Across the country, you want to be able to make sure that you're comfortable. I think that's priority one. Well, when you walk into a basement like that where it's very cold, but it's high humidity, what we have going on is it takes less um, what's the word to put cooling, I guess you would say, less BTUs to change the temperature of a basement than it would a main floor of a home or a, I guess, a second story of a home, even still. Uh but when you have a dehumidifier put in place, what we usually run into, this is what I see 99% of the time, is they will have an air conditioning system that's oversized for the entire space, which means that it's short cycles. And to your point, if there's not a need to cool, then the air conditioning system's not going to come on, which means that no humidity is going to get removed. Uh now, the dehumidifier, it's a little bit different. So if you've ever seen, and you can go to their website if you want to see it, on the front portion of all of our dehumidifiers, it's a standard that it has a user interface control that's going to read temperature, humidity, inlet and outlet temperature and humidity as it goes to that unit. So you're getting a full uh spectrum, I guess you would say, on what that room is actually doing. So where it would read, let's just say it was 60 degrees in that basement, you know, it's cold down there, but it's 80% humidity, we're gonna prioritize that humidity and we're gonna get that reduced. So, what it would do to acclimate for that is it will try to cool that air to the point where it's going to uh basically condense and then it's gonna heat that air and pull it back out. So it all happens in one in one setting, one spot, and it's calculating dew point. Whether we want to see RH or not on the front of that unit, we have to know the dew point in order to produce that. Most thermostats in homes do not do that. Uh, there are some in the market. I know we actually we manufacture a thermostat that can that can do both, um, but you're either going to run the air conditioner a lot longer, which means it's gonna make it a lot colder down there. Uh so that's not efficient and that's not comfortable. So that's where the dehumidifier is a that's the prize winner for that. Because, like to your point, it may only run one or two times a year just to acclimate the space. But once it's acclimated, we're we want to stay in the spectrum of how do we get this monitored and changed actively, not over the course of how long the air conditioner runs. Yeah, that's a good point.

SPEAKER_01: 8:20

I I appreciate you sharing that because uh, you know, even in the crawl spaces, there was this phenomenon for and it probably still goes on, but there was a lot of HVAC contractors that were, oh, we don't need to put a DHU down there. Let's duck, you know, uh a supply and a return in the crawl space. And again, it was the same thing. We'd go into these crawl spaces, and because the thermostat was in the living space, you know, either the DHU would short cycle or not cycle long enough to control humidity in the crawl space. You know, the dehumidifier is is designed to control humidity. The HBAC system is designed to control temperature. You know, they're two totally different things in a lot of ways, and they they can feed off each other a little bit. You know, the dehumidifier can help the AC run less if the humidity is lower and all that, but but they are two different mechanical devices that have two different purposes, right?

SPEAKER_00: 9:13

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