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Old 11-16-2009, 02:05 PM   #1
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Need to dry out my garage


Need your help guys!

I have a 20' x 20' attached garage that is extremely high in humidity. It is on the north side of my house, on a concrete slab, with insulated concrete form perimeters. Both the walls and ceiling are well insulated, and the only thing bringing house air into it is the central vacuum exhaust. My wife parks her car in the garage, and I recently installed a small natural gas radiant heater (25,000BTU) to melt the snow from the car. Works great, aside from the stink. The garage has a good drain in the floor. I'm aware that the car is bringing a fair bit of moisture into the garage, but we best not go there... As she points out, we had moisture issues there before she parked in it.

Here is a link to the heater I've installed. Local building codes do not require external venting for a heater of this size, although the mfr. specifies an open 8" hole in the wall for fresh air. I haven't done this yet.

http://www.mrheater.com/ProductFamily.aspx?catid=50

The garage is presently sitting at 78% humidity, while the house is around 45%. Outside temperatures are around freezing, but it typically sits around 10 degrees (Celsuis) below zero here in northern Canada. My window is dripping, as are the door hinges, and the garage door door. A bit of black mold starting in the corners too... yuck.

Any suggestions on where I should start? I'd prefer to try and reduce/eliminate the source(s) of humidity before I throw any power (dehumidifier, power vent, etc) at it.

thanks for your help. This is a great forum....

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Old 11-16-2009, 02:14 PM   #2
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Need to dry out my garage


A. Drywall the ceiling(less heat needed, heater won't run as long).
B. Get rid of that heater, and get a vented one(unvented heaters add moisture to the air).
C. Increase the temp in the garage(warmer air can hold more moisture, and have a lower RH).

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Old 11-16-2009, 02:48 PM   #3
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Need to dry out my garage


beenthere:

the ceiling is drywalled, and has 18" of insulation above it. Not much heat needed to warm this space.

I've just installed the heater, and I think the garage is probably still adjusting to the higher temperatures. Getting rid of it really isn't an option I'd like to pursue right now, but I could punch a vent hole through the wall if I thought it would help.

I'm wondering if the concrete slab is wicking moisture? Should I be sealing it?
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Old 11-16-2009, 05:08 PM   #4
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Need to dry out my garage


Won't hurt to seal the concrete.

But, non vented heaters, always add humidity to the room they are heating.
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Old 11-16-2009, 09:54 PM   #5
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Need to dry out my garage


As stated, non-vented heaters add moisture to the air--period! Most non-vent heaters have an option to add a vent, your's may. One option for you would be to get a de-humidifier and run a line from the drain to a floor drain or outside, to prevent having to empty the bucket so often.
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Old 11-25-2009, 06:41 PM   #6
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Need to dry out my garage


Hey longshanks - What area of town are you in? I'm in Malaspina Ridge (College Heights). I've built 2 of my own homes now... one in Abbotsford and one here, so I have decent experience with both moisture (the coast) and cold & snow (here). My garage is nice and dry, and with reference to your skylight issues in other posts, I also have 5 skylights in my home here in PG, and I've had no problems with them - I'm sure I can impart some experienced wisdom to you on both topics, but a face-to-face discussion is where you'd probably best start. What's your schedule look like? Want to meet up for a Timmys double-double?
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Old 02-04-2010, 03:09 PM   #7
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Need to dry out my garage


thought I'd follow up with this in case the information is useful to others.

In short - the unvented unit went straight back to the store after I tried it out. As many of you posted, it shot the garage humidity up to around 90%, and reeked like crazy. I replaced it with a vented heater, and although humidity levels are still high (around 65%) they are better than before. Next step will be to seal the slab and see if that makes a difference.

Thank you to all who responded, including Mr. PG who was very helpful.
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Old 02-04-2010, 09:35 PM   #8
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Need to dry out my garage


Get a dehumidifier as well and maybe an industrial fan to make sure there's lot of air flow. Will help move the heat around too.

Also not sure how an unvented heater would work given the CO / CO2 needs to go somewhere, and the combustion also creates an acidic substance that would normally need to go somewhere. I'm guessing it's going in the air which is causing the high humidity and smell. I would definably get something vented, even an electric heater (which does not require any vents, which can lose heat), but gas will probably be cheaper to run.

Last edited by Red Squirrel; 02-04-2010 at 09:37 PM.
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Old 02-04-2010, 09:49 PM   #9
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Need to dry out my garage


You probably have no vapor barrier (6 or 10 mil) under the slab, so moisture is available.. Not much that can done about that mistake, but it could help in minimizing the the effects and making it more usable.

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Old 02-07-2010, 11:29 AM   #10
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Need to dry out my garage


I've put a vented forced air NG heater in there, and it's much more comfortable to work in, but although humidity dropped about 20%, it's still hovering around 65% on average at this time of the year.

I also suspect there wasn't a vapour barrier put under the slab. Would a silicate sealer solve this problem?

thanks for the feedback.

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