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I read so many contradicting things online: Some recommend dehumidiers (if so, which?), some advice against. Some recommend fans (which, how many, how/where to install?), some advice against. Some advice so seal the vents, some advice against. And yet others recommend to seal all vents but one.

I assume the reason is it highly depends on location (climate), vented vs unvented, dirt vs non-dirt.

I am located in the Bay Area (California), so for most time of the year the humidity outside is low so vented crawl space seems to be OK (I have been told).

However, I am impacted by this atmospheric river which made water seep into the crawl space (and unfinished basements): The concrete perimeter foundation and sill plates are soaked and in the part with the unfinished basement the floor is wet (little bit of standing water). I see fungus growing.

  • Current measured humidity is 76.4%
  • Total crawl space size: ~1100 sqft
  • 4 vents (each corner)
  • Crawl space has two parts:
    • a small unfinished basement (small standing water, fungus growing on the floor, see attached picture)
    • A larger crawl space (concrete perimeter, sill plates and wood is wet throughout the perimeter, see attached picture)

What is the most effective and quick way to dry this out as soon as possible?

Crawl Space

Unfinished Basement

divB
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4 Answers4

7

Fastest, without tearing the house apart:

4 fans sized to your 4 vents - two blow in, two blow out. Less fans will probably work fast enough, but 4 would fit "fastest" as requested. If you have prevailing winds, agreeing with them rather than fighting them will increase effectiveness when choosing fan directions.

Type of fan, judging by the (apparently) fairly small visible vent in one picture: In-line duct booster fan or similar. "Mixed flow axial" might be best. Depends how much you care about efficiency - you presumably won't be running them 24/7/365, just until you get the basement dry. I like the air movement .vs. power of the more efficient "radon fans" or the ones that have flooded the market to serve "indoor plant enthusiasts" which can be had with similar airflow/pressure/power ratings while not being restricted to vertical mounting as most radon fans are. But I was solving a radon issue and then looking at a heat balancing issue with long-term running in mind. The "plant ventilation" ones were something I stumbled across while looking for something else. That may be what I get for the heat balancing job, as they are like half the price without going to direct Asian import junque.

Additionally, any other fan you have handy to stir around the air inside the basement/crawlspace. If you somehow don't have other fans, they do sell "drying fans" specifically, which are a sort of plastic-cased squirrel-cage fan, typically, with an outlet right at floor level, but whether any will be in stock where you can get them is debatable. A plain old box fan or oscillating fan you probably already own will do what you actually need on that front well enough for no extra investment.

Ecnerwal
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4

For standing/very wet surfaces fans will be the best(besides mopping/sponging/pumping).

You want a good breeze blowing in from one end and out the other.

Amount of fans will depend on area.

crip659
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3

In a pinch a portable or window air conditioner may be some help. Just haul it in there and let it run so that the hot and cold side are both there in the crawlspace. It's not a purpose-built humidifier, but it could:

  • warm the air under the crawl space, increasing its capacity to carry moisture
  • if the evaporator coil can get cold enough it'll actually de-humidify the air. Leave a pan or bucket or something to catch the liquid water coming off the air conditioner before it drips back into the soil.

I wouldn't be so confident in this approach as to go out and buy a new air conditioner, but if I already owned, could easily borrow, or could inexpensively buy a used one, I'd give it a shot.

Greg Hill
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-1

Natural ventilation is totally preferable, if your local atmosferic conditions are favourable. Forced ventilation might help, but it won't do a magic.

Good dehumidifiers can definetely resolve the problem (or bridge period of time), if ventilation doesn't help. You want hi-performance unit, one with integrated heat pump. Some 30 to 50L/day (~10 gallons/day) would definitely help quickly. They require about 600W at full power, when you need to remove humidity agressively. They're not cheap, starting around $400 I guess, but in many places they can also be rented.

Based on your description, I assume you're in building process and you will eventually take care about the source of the problem - which should be the ultimate aim. Simply put, humid warm air gets to colder surfaces, causing condensations and this has to be prevented.

Oak_3260548
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