Crawl space dehumidifiers, sized on pints per day

For the ordinary case — a crawl space somewhere between 1,000 and 2,000 square feet, a dirt or barrier floor, and no floor drain anywhere in it — the pick is the ALORAIR ALORAIR Wi-Fi 70 PPD Dehumidifier with Pump for Crawl Space and Basement. It is rated 70 pints per day on the modern scale, which is comfortably above the 26 pints per day a 2,000 sq ft wet crawl space works out at, and it has the condensate pump built in.

That last point is the one that decides it. The version of the same machine without the pump, the ALORAIR 70 Pints Energy Star Crawlspace Dehumidifier Up To 1000 Sq.Ft., is $31.62 cheaper — and a standalone condensate pump costs $56.04. Buying the pump separately to save $31.62 loses you money and gains you a second box to trip over in a space you have to crawl through.

Four situations, four different answers. Find yours and stop reading the other three.

The cheapest way to get a dehumidifier into a crawl space is to carry down the same household unit you would put in a laundry room. People do it constantly, and it works for about one season.

The reason it stops working is temperature, and it is exactly the same physics that forced the 2019 rating change. A refrigerant dehumidifier pulls water out of air by dropping that air below its dew point on a cold coil. The colder the incoming air, the colder the coil has to run to stay under the dew point, and the closer that coil gets to freezing. In a 60°F crawl space at 70% relative humidity the dew point is 50.2°F — the coil has to be colder than that to condense anything at all, and a household unit’s coil in those conditions spends a large part of its cycle iced over.

A frosted coil does not remove water. It removes airflow. The fan keeps running, the compressor keeps running, the power meter keeps turning, and the bucket stays empty — which is precisely why the usual verdict is “the dehumidifier broke” rather than “the dehumidifier was the wrong machine.”

Units sold specifically for crawl spaces are built around this: a defrost cycle that reverses or bypasses the coil before ice builds, a coil and fan sized for continuous low-temperature duty rather than for a hot laundry room, and a sealed case that survives being left on a damp floor for a decade. We cannot verify a minimum operating temperature for any unit from listing data — nobody publishes it in a form we can compare, so treat that as the one specification worth pulling off the manufacturer’s own sheet before you buy, whichever model you land on.

The same dew point arithmetic is also the reason the target is a band and not a floor. Pull that 60°F crawl space down to 50% RH and the dew point drops to 41.3°F. Every duct, pipe and joist down there is now above the dew point, so nothing sweats — which is the actual goal. Chasing a much lower number buys nothing and costs electricity.

Our sizing function takes a crawl space flag, and when it is set it multiplies the duty by 1.4. We want to be plain about what that number is: it is a practitioner rule of thumb, not a standard, and we use it and say so rather than presenting it as a published figure. There is no AHAM crawl space table. What there is, is broad agreement among people who install these things that an unconditioned space taking moisture up through soil needs meaningfully more capacity than a living space of the same floor area, and +40% is where that agreement sits.

Here is what it does to the numbers, for a crawl space in the “wet” band — visible beads of moisture on the plastic, a floor that is damp to the touch.

Two things fall out of that table that are worth saying out loud. The first is that the crawl space modern-label column and the plain old-scale living-space number are almost the same figure, because 1.4 × 0.71 = 0.99 — the crawl-space uplift and the DOE derating very nearly cancel. That is a coincidence of two unrelated numbers, not a rule, and it stops being true the moment either one is revised. We mention it only because it explains why a lot of old contractor advice still lands in roughly the right place despite being on the wrong scale.

The second is that these duties are small. A 2,500 sq ft wet crawl space works out at 30 pints per day, and our pick is rated 70. Capacity is not why you buy a crawl space unit. You buy it for low-temperature operation, defrost, drainage and the ability to run continuously for years — and the pint headroom is what pays for the fact that the machine will be working at 55–60°F rather than the 65°F it was rated at.

Every one of these listings advertises a coverage area, and it is the figure most buyers actually shop on. It is also the one number in the category with no standard behind it. Here is our whole corpus of units tested at 70 pints per day — the same tested capacity, 6 different machines — with the coverage each manufacturer prints on its own listing.

Identical tested capacity. Claims spanning 1,000 to 4,500 square feet, a factor of 4.5. Nothing about the machines changed between those rows — only the marketing department did. That is why COVERAGE_CLAIMS_COMPARABLE is false in our source, and why every recommendation on this site is made on pints per day, which is tested against a written procedure, and never on square feet, which is not.

Read the low claims as a hint about intended use rather than a limit: the units claiming a thousand square feet are the ones built for crawl spaces, and their makers are describing a sealed, unconditioned space rather than an open floor plan. That is useful context. It is not a specification.

In a basement you can get away with a bucket for a while, because someone walks past the machine every day. Nobody walks past a crawl space. A bucket-only unit in a crawl space is a machine that runs for two days and then stops on a full-tank sensor for the rest of the summer, and you will not find out until you next go down there.

So the water has to leave continuously, and there are exactly two ways it can: gravity or a pump. Gravity is better when it exists — no moving parts, no power, nothing to fail. It requires a continuous downhill run from the machine’s drain port to somewhere the water is allowed to go: a sump pit, a french drain, or daylight if the grade falls away from the house. If you have that, use it, and buy the unit without the pump.

Most crawl spaces do not have it. A crawl space is by definition close to grade, often below it, and it almost never has a floor drain. That is why a condensate pump is not an upgrade in this category, it is the default, and why we prefer the version of the pick that ships with one integrated.

If you are pumping into an existing waste line rather than out to daylight, check your local code first — many jurisdictions require an air gap or trap and some prohibit the connection entirely. That is a genuinely local question and we are not going to pretend otherwise.

A standalone unit sits on the barrier, pulls air in one side and pushes it out the other. It works when the crawl space is one connected volume that air can circulate through. In a rectangular space under 2,000 square feet with no interior foundation walls, that is usually the case, and a standalone unit is the right answer.

Ducting earns its cost in one specific situation: a crawl space chopped into bays by interior piers or block walls, where one leg is effectively a separate room the machine can never see. Air does not migrate through a masonry wall. A unit with ductable supply or return lets you take the dry air to that far bay and pull the damp air back, which no amount of extra capacity in the main space will achieve.

For that, and for spaces past roughly 2,000 square feet, the ALORAIR ALORAIR 113 Pints Crawlspace Dehumidifier for Commercial, Sentinel HD55 is the pick — 113 pints per day tested, 1,193 reviews, and duct collars as standard. Note that it does not have an integrated pump, so budget the $56.04 condensate pump alongside it unless you have a gravity route.

The honest caveat on ducting is that it is the part most likely to be done badly. Flex duct crushed under a joist, or a supply run with no return path, will do less for you than the same machine sitting unducted in the middle of the floor. If you are not going to run it properly, do not run it at all.

If the floor of your crawl space is bare soil, yes, and it is not close.

The reason is the shape of the load. In a living space, moisture arrives in bursts — someone showers, someone cooks, laundry dries. In a crawl space over bare earth it arrives continuously, all day, every day, from a source that does not run out. Soil evaporation is not a moisture event the dehumidifier has to catch up with; it is a permanent supply the dehumidifier has to match forever.

A vapour barrier does not remove water. It removes the supply. Ten mil polyethylene across the soil, lapped and taped at the seams and run up the foundation wall, converts an unbounded moisture source into a bounded one — after which a modest dehumidifier holds the space easily, and before which a large one runs continuously and still loses.

The full commercial version — reinforced barrier, sealed vents, insulated walls, conditioned air — is a multi-thousand-dollar job and often worth it. The version that does most of the work is a roll of barrier and a roll of seam tape, and it is the single highest-return thing you can do down there. Do that first, run a hygrometer for a month, and size the dehumidifier against what is left.

And the case where the answer is to buy nothing at all: if the barrier is already down, the vents are managed, and a cheap hygrometer reads under 50% relative humidity through the worst weeks of August, you do not need a dehumidifier. Adding one would cost you a few hundred dollars up front and a running cost every month to hold a number you are already holding. Keep the hygrometer, check it after heavy rain, and revisit the question if it climbs past 60%.

How any of these units perform at 50°F. That is the number that would actually decide this category, and no listing in our corpus publishes capacity at a second temperature. We are not going to model it, because a modelled derating curve presented next to tested figures would read as though it were measured.

How loud they are. Several listings advertise a decibel figure in the title. None of them state the distance or the load it was measured at, which makes the numbers uncomparable, and a crawl space unit sits under a floor rather than under a bedroom, so it matters less here than it does in a basement.

How long they last. Amazon review counts tell you how many people bought a listing, not how many units survived five summers. We show review counts as screening data, with the date they were captured, and they are Amazon’s numbers and not ours.

For anything that turns on your specific foundation, grade or local code, a crawl space contractor who will physically look at it beats every page on the internet including this one. We do not earn anything from sending you there and we are saying it anyway.

If you want to run the arithmetic on your own numbers rather than ours, the calculators take a floor area and a dampness band and return the duty on both rating scales. If you want the background on why there are two scales at all, that is in the guides.