How to reduce humidity in sealed concrete cellar

3 years ago

Hi,

We have a safe room in our basement that we've converted into a storage area and cellar. The room is solid concrete- floors, walls, ceiling and has one door. You access the safe room behind a trick bookshelf in our basement. I've ran into a moisture problem this winter. The temperature in the fall and winter months is a pretty consistent 50 degrees, but the humidity is fluctuating between 88-98%. Consequently, there is a musty smell and we've had a bit of mildew on some storage containers in there. In the 2 corners of the ceiling that are against the outside (as in they don't share a wall with the house), there was some visible condensation. I'm trying to figure out the most efficient and economical route to address this issue.

There is one vent in the room that has a pipe attached to it and the pipe sticks up outside the back of the house. The original owner had attached some ducting to a small dekstop fan and attached that to the vent hole. I recently stuck a box fan in the room to circulate some air, and replaced the small desk fan with a small ventilation fan used for grow tents to suck air from the safe room to the outside via that vent. It has a much higher cfm than the desk fan, but I have not noticed any significant change in the humidity levels doing this. Both fans have been running continuous for a week. The condensation on the ceiling corners are much improved though.

I have a standard dehumidifier coming in the next week to try out and I'll drain that straight into the floor drain in the room. Does anyone have any other suggestions on how to reduce the humidity levels in a room like this econimically? The room is roughly 1500cu/ft (14x14x7.5) I stained and sealed the concrete floors when we purchased the house, and I was curious about whether using a product like DryLok on the walls and ceiling would offer any help? I've ready using DryLok can sometimes make a humidity issue worse and I certainly don't want that in an already compromised room.

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worthy

3 years ago

We've been using dehumidifiers in our basements for nearly 4 decades and the electrical costs are negligible when weighed against the benefits.

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Comments (6)

sktn77a
3 years ago
"I've ready using DryLok can sometimes make a humidity issue worse and I certainly don't want that in an already compromised room."

Only if the moisture is getting in from some other source.

If the dehumidifier draining into the floor drain doesn't work, you may want to consider blocking it off and installing a condensate pump and drain hose out of that vent to the outside in the ceiling (and seal any gaps there).
Tyson T
Original Author
3 years ago
There's also a utility sink and toilet in that room. Would draining into the sink be any better?
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sktn77a
3 years ago
Possibly. They key is to keep the condensate from evaporating back into the space.
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Charles Ross Homes
3 years ago
Hi, Tyson,

Since you're using the space as a storage room and not it's intended purpose as a "safe" room, you need to control the conditions in the space to meet the requirements of whatever you are storing in it. If you're storing plastic toys, the requirements will be different from those required to store books and papers or fine wood furniture.

For your health and that of your home, you should get the relative humidity below a level that will sustain mold growth. I believe the general consensus is that keeping the relative humidity around 50% will do that. If the relative humidity without conditioning the space is around 90% at 50F you could lower it to 50% +/- by simply heating it to 70F or you could run a dehumidifier to lower the humidity or some combination of the two. Concrete is great at storing and transporting moisture. You'll need to do something to reduce moisture migration through the walls, and possibly the floor, too or you'll be paying a lot for dehumidifying the air and continual moisture removal from the concrete.
Tyson T
Original Author
3 years ago
Hi all, thank you for your responses. I wanted to give a quick update from this weekend. I did purchase a standard condenser type dehumidifier and put it in the cellar. The humidity was at 85% when I started it and dropped to about 55% in 36 hours in continuous mode. May have dropped more, but it shut off when the tank got full. After emptying approximately 2 gallons and 48 hours later I've got the humidity down to 50% and the temperature raised to 55 degrees. I've got it plugged into a meter which tells me its using 240w in continuous mode on high. I'll be putting a hose on it to drain into the floor drain soon and am curious to see the total energy used going forward to keep it between 45-50%. I also noticed there is no moisture in the ceiling corners near the exterior side of the room and the concrete is no longer dark in those areas. I'm wondering now if water wasn't actually seeping through the ceiling in those corners, but rather condensing there.

If I can keep this under control for a couple KW/day I'll be happy with this setup. We had solar installed at the end of summer to provide 110% of our calculated electrical consumption, so I'm hoping this won't make a difference with scaling up our solar.