How to Know If Your Crawl Space Dehumidifier Is the Right Size
Introduction
Dehumidifier Sizing Done Right
WHY SIZE, PLACEMENT, AND SETUP ALL MATTER
This is something I deal with all the time on inspections.
A homeowner calls because they're having moisture problems, humidity issues, maybe even structural damage.
They already had crawl space work done.
They already paid for an encapsulation. But something still isn't right.
I was in one yesterday.
Over 2200 square feet, and the dehumidifier was an E70 sitting six feet from the door, shoved up against the wall.
The unit was completely clogged. Never been serviced.
And there was no moisture sensor, so they had no idea their crawl space was still holding humidity.
Meanwhile, they're dealing with structural issues and don't realize it's all connected.
That's what happens when the details get skipped.
The job looks done, but it's not actually protecting the home.
So let's talk about what proper dehumidifier sizing looks like, why placement matters just as much, and how you can check this stuff yourself before you pay anyone a dime.
How Dehumidifier Sizing Works
Dehumidifier sizing is based on square footage. It's not complicated, but it does matter.
Here's the breakdown I use:
- E50 – Up to 1600 square feet. I don't use these often unless the crawl space access is too tight to fit a larger unit.
- E70 – Up to 2200 square feet. This is the standard I install on most jobs.
- E80 – Up to 2600 square feet.
- E100 – Up to 3200 square feet. I use these on larger crawl spaces, and I don't upcharge for it. It's just part of doing the job right.
If you have more than one crawl space and the access between them is blocked or too small, you're probably going to need two units. One dehumidifier won't dry out two separate spaces. It doesn't work that way.
The point is, the unit needs to match the space. An undersized dehumidifier running all day isn't going to solve your moisture problem. It's just going to run up your electric bill while your crawl space stays damp.
Why Placement Matters Just as Much as Size
Here's something a lot of people don't realize. Dehumidifiers work by radius. They pull moisture from the air around them, not from the entire crawl space all at once.
That means placement matters. You want your unit in the center of the crawl space, or as close to center as possible. If there's ductwork or something in the way, you work around it. But the goal is always to get that unit where it can reach the whole space.
What I saw yesterday was the opposite. The dehumidifier was six feet from the door, pushed up against the wall. It wasn't reaching the rest of the crawl space. The far corners were still damp, still holding humidity, and the homeowner had no idea because there was no moisture sensor telling them anything was wrong.
If your dehumidifier is sitting right next to the access door, that's a red flag. That's a sign someone wanted to get in and out fast. These units aren't hard to move. You put them on a cart with wheels and roll them to the center. It takes a few extra minutes. But those few minutes are the difference between a system that works and one that doesn't.
Other Red Flags to Watch For
While we're on the subject, here are a few more things I see that shouldn't be happening.
Extension cords. If your dehumidifier is plugged into an extension cord, that's a fire hazard. It should never be set up that way. You need a dedicated circuit ran from your breaker box and a GFCI protected outlet in the crawl space. That's the proper way to do it.
No moisture sensor. If you don't have a way to monitor humidity levels, you won't know when something's wrong. The homeowner I visited yesterday had no sensor. Their unit was clogged and barely running, and they had no clue until the structural problems started showing up.
Unit never serviced. Dehumidifiers need maintenance. Filters get clogged. Parts wear out. If the unit has been running for years and no one has touched it, there's a good chance it's not doing its job anymore.
These aren't small things. These are the details that separate a crawl space that's actually protected from one that just looks like it is.
How to Check Your Square Footage
Here's something you can do yourself before you ever call a contractor.
Look up your crawl space square footage. It's easy.
Google "Tennessee property data." Find your county. Type in your address. You'll see your first floor square footage right there. That number tells you what size dehumidifier your crawl space actually needs.
If a contractor quotes you an E50 and your crawl space is 2000 square feet, that's not going to cut it. If they're putting in an E70 for a 3000 square foot space, same problem.
Know your numbers before anyone gives you a quote. It takes two minutes and it helps you ask the right questions.
How We Handle Dehumidifier Sizing
At Crawl Logic, the E70 is our standard. It covers most crawl spaces we work on, and it gives homeowners solid performance without overdoing it.
If the access way is tight, I'll use an E50. If it's really tight, I'll do two E50s to make sure we're getting proper coverage. For larger crawl spaces over 2000 square feet, I go with an E100. And I don't upcharge for that. It's just what the space needs, so that's what we install.
When there are two separate crawl spaces with a blocked or narrow access between them, we put in two units. One dehumidifier isn't going to dry out two spaces. That's not how it works.
Every unit gets placed in the center or as close to center as we can get it. Every unit gets a dedicated circuit and a GFCI protected outlet. And every job includes a moisture sensor so you actually know what's happening down there after we leave.
That's not extra. That's just how it should be done.
What to Ask Your Contractor
If you're getting quotes for crawl space work, here are a few questions worth asking:
- What size dehumidifier are you installing, and why?
- Where in the crawl space will it be placed?
- Is it going to be on a dedicated circuit?
- Will I have a moisture sensor to monitor humidity after the job is done?
These aren't trick questions. Any contractor who knows what they're doing should be able to answer them without hesitation. If they can't, or if they brush you off, that tells you something.
The goal isn't to become an expert on dehumidifiers. The goal is to know enough to protect yourself from a sloppy job.
Ready to Get Your Crawl Space Right?
If you have questions about dehumidifiers, sizing, placement, or anything else going on in your crawl space, reach out. I'm happy to walk you through it.
We offer free inspections for homeowners in the Nashville area and surrounding counties. I do all the inspections myself. No salespeople, no pressure, no gimmicks.
Just an honest look at what's going on under your house and a straightforward conversation about what you actually need.
You can call or text me directly. I'll answer your questions, show you exactly what we're seeing, and let you decide what makes sense for your home.
That's how we do things at Crawl Logic.
