120V Radiant Floor-Warming Mat in a crawlspace

[Stumpy]

I've got a moisture problem in a large crawl space area. There is efflorescence on the soil and nearby concrete foundation. It is a well ventilated space, but the ground just has a lot of water. Instead of installing a forced air heater which would just blow much energy out the vents, I thought about burying an electric radiant floor heating mat in the loose soil in the lowest, wettest spot. This one only uses 180 watts though $150 for the mat, and $70 for the thermostat seems a little steep.

Do you think the mat would work OK covered with loose, sandy soil in a completely unoccupied area? Maybe staked out with markers so some future handyman doesn't get a surprise?

[trader_4]

Couple of problems. One is, I doubt 180W is going to heat 180 sq ft of soil much. Second is, even if it does, that may just make things worse, ie making more water evaporate and enter the air. Third, it probably will run most of the time, and every 5.5 hours you're using

1 Kwh of electricity. Around here, that would be about 50 cents a day. Isn't the more typical aproach to put down plastic sheeting to keep the moisture down?

[Stumpy]

The way the white crystalline stuff comes out of the concrete, I think if I put plastic over the soil, it might come up in the wall instead.

There are many vents so I'm not so worried about the vapor finding its way out.

I'm not really sure this is going to happen. Just wondering if the mat could take the environment.

[bob haller]

Well how about a interior french drain around the permiter, drained outside, then cover everything with heavy mill plastic, taping the seams. put iinsulation on the walls, seal all the vents, then add a little heat.

this should do the job, and help the room above to be warmer too

[trader_4]

I take it the portion of the wall where the efflorescence is appearing is below grade? I doubt putting moisture barrier on the bottom of the crawlspace is going to affect most of the wall area. Maybe close to the bottom, only, if at all. What water is higher up in the ground is there regardless. What's the situation outside, ie with gutters, downspouts, grading? Been out there in a heavy rain to see where water is really going, despite where you think it goes?

Unless a proper, modern water barrier is installed correctly around the foundation on the outside, some amount of efflorescence is probably inevitable in many block type foundations in areas with enough moisture.

It's sure not intended for that application. It can withstand water, at least temporarily, since it's intended to be embeded in concrete. But long term, it's anyone's guess. But I think it's a bad idea for all the other reasons regardless and I doubt it would have much, if any benefit.

[Stumpy]

That's a lot of work. If I seal the vents, then the vapor will just hang around and grow some mold or something. The water is not actually pooling, just growing those hairy crystals.

[Stumpy]

This became much more noticeable when the neighbor (~3' higher yard w/ retaining wall) put in an irrigation system. I assume that the water is hydraulicing under my house. He reduced the duration of his program but my problem persists.

Just exploring options. The mat would be easy to install.

[trader_4]

I guess that could be a factor, but I would think it would take a hell of a lot of irrigating. With the typical home irrigation system, you have to run it for more than an hour per zone to put down even 1/2" of water. If you put out some empty tuna cans, it's surprising how long it takes to get a decent amount of water. Of course it depends on the flow rate, how ofter he's watering, etc, but I'd be surprised if that water is making it's way to your crawlspace.

[Tony Hwang]

Hi, My cabin's crawl space floor is pretty dry year round. I have one hot air duct run into the space from furnace installed their. And good vent to outside. Never have moisture build up problem over 15 years.

[clare]

I'd insulate the floor and apply a good vapour barrier, then force ventilate the crawl space. Spray goam on the bottom of the floor would provide insulation and vapour barrier in one. Insulate the heating pipes as well and make sure all water pipes, if any, are on the warm side.. If there is still a problem, dig a trench between your foundation and the neighbour's retaining wall and install a perforated drain pipe with soil filter sock and drain it out to a low spot or a sump pit where you can pump the accumulated water out. Much better to prevent the water from getting into the foundation than to draw the water through the foundation using an "internal french drain". )What did the french ever provide in the engineering world that was worth emulating??)