My Garage Humidity Saga...

[longshanks]

Hello from Northern Canada eh!

I've already done a bunch of searching and reading on this site, and although I have some ideas on what I might do next to reduce my garage humidity, I thought I'd post some details and see if any of you are able to help.

The attached garage is 20x20 with a floating concrete slab. We bought the house a year ago so I can't tell you if the slab has vapour barrier under it or not. There are insulated concrete form walls surrounding the garage, with a gap of about 1/2" between the edges of the slab and the ICFs. The ceiling is covered with at least 18" of blown in insulation, and the house has 2x6 walls, well insulated. Both the main door and the man door are reasonably well insulated.

When we bought the house, there were creepy dark mold stains in the corner of the garage on the gyproc, and my humidistat tells me that the garage is at about 75% humidity on average. The car and snowblower live in there, unless I'm taking on a woodworking project. If you think you can talk mrs. into parking her car outside, you have an open invitation. I'll put on the popcorn

I just sunk a fair amount of $$ into a vented 45K BTU natural gas heater, and I have it set to keep the garage temperature above 5 degrees celsius or so. Winter temperatures here probably average around -8 degrees celsius. The forced air heater has a fan that comes on when the thing cycles. I had to cut a 4" vent through my wall for intake air. This heater warms the place up quickly, but I'm concerned about the cost of running it constantly.

Any ideas on what I should be doing next? Right now I'm guessing the potential solutions are to either

a) stop being so cheap and turn up the heater
b) try sealing the slab with some sort of a silicate deep sealer
c) buy a de-humidifier
d) put my foot down and tell mrs. to park her car in the snow bank

standing by...

cheers

 

[Photo]

longshanks,

Where abouts in 'Northern Canada'?

Here in Alberta, we're normally pretty dry and have to add water to the house in the winter, not worry about removing it!

A dehumidifier may be your answer, but do you have any place to run the drain line (or will have to keep emptying it constantly)?

Personally, I would turn the heat up a little (~ 10* C) and run the dehumidifier.

Lane

 

[rwhite692]

+1 for getting a Dehumidifier and run a drain line outside.

 

[longshanks]

I'm in northern BC. It is generally a humid area, but winter temperatures often go to 30 below.
I don't mind trying a humidifier, but I'd ideally like to do what I can to prevent the problem, and then rely on my heater and potentially other powered devices only if needed. If I have to get a humidifier, I could run the drain line to the garage drain, no problems there.

Having read a bunch on here already, I suspect that the main garage door is a large part of the problem. Even though it's insulated and tightly weather stripped, it freezes along the cracks and is constantly wet on the inside through the winter. But why seal it up any tighter when there is a 4" vent in the adjacent wall?

Thing is, why do some other people in this area not have this problem?

 

[erda]

A friend in Edmonton has a similar problem, although his is brought on by the melting of snow & ice off his car. His solution is to install an exhaust fan at floor level in the opposite corner from his heater. IIRC he keeps the temperature at 5*C also.
I don't have the same issue as we don't get as much snow, and I usually try to "kick" it off before I park in the garage. Also have a floor drain, if that makes a difference.

 

[bucs012]

It's mentioned above to install a hose to drain and run it outside. Are there any of you that do that and live in a cold climate area? I live in Iowa and the winter has been snow, ice and cold...minus 15 to +20 on a good day!

What would be the best way to run a tube outside and protect it so that it does NOT freeze?

At first thought, I would be best to run the dehumidifier UP on a work bench to elevate it so the drainage would run DOWN and outside a small hole in the side of the garage?

My garage does not have a floor drain.

 

[diogenes]

It's mentioned above to install a hose to drain and run it outside. Are there any of you that do that and live in a cold climate area? I live in Iowa and the winter has been snow, ice and cold...minus 15 to +20 on a good day!

What would be the best way to run a tube outside and protect it so that it does NOT freeze?

At first thought, I would be best to run the dehumidifier UP on a work bench to elevate it so the drainage would run DOWN and outside a small hole in the side of the garage?

My garage does not have a floor drain.

Two options, the first as you suggest: Plumb it so that any water in the line drains completely out by gravity, the end of the line elevated above the ground a couple of inches. Use black line outside to take advantage of the suns heat to keep the pipe from getting cold enough to freeze the water on its way down the line. The down side would be that a trickle of water coming out of the humidifier could get cold enough to freeze and build up to a blockage.

A second choice, that may be best if it is really cold, put a bucket in the heated space for the water to drain into and then use a small sump pump to empty the bucket when it fills. That would allow you to have sudden flushes through the line and it would not have a chance to get cold enough to freeze the line as the water trickles out... Use black hose, natural drain, etc.

 

[RossABQ]

At least in the states, a floor drain in a garage is not allowed, because of the potential for oil/etc to go to sanitary sewer. It used to be OK so there are a lot of older ones that have it.

It sounds like slushy cars parked in the garage are the source of water into the garage? If so, I hate to say it but you would be better off letting the garage go cold (just below freezing), so it doesn't melt. Warmer temps also allow salt to do its nasty deed.

About the only other practical alternative is to use an air-to-air heat exchanger to bring in cold, dry outside air to flush moist air out, without running up a big energy bill. These recover the energy in the inside air, transfer it to the fresh air, but don't transfer the moisture. You would need to move more air than a 4" vent will handle.

 

[longshanks]

hmm... some interesting ideas. It seems that most of your suggestions so far are directed at handling the symptoms of the problem, as opposed to the source of the problem. Having spent far too much time already thinking about this, my theory is that the humidity is coming from either a) moisture under the slab, which the slab is wicking into the garage, or b) wife's car and the dripping snowblower. The garage has a floor drain that is working, although the grade of the slab is not perfect, and some water escapes around the edges of the slab and goes to the ground...

As my wife would point out, the garage humidity problem existed before she started bringing her car in there. No argument that the snowy car isn't contributing to the problem, but it sure isn't helping.

I have turned the thermostat up to 10 degrees celsius and we'll see if it makes a difference. Was at 72% RH this morning. One observation is that it is very stagnant in there. No air circulation until the forced air fan comes on and blows the air around a bit.

The exhaust fan is an interesting idea. Is it hooked up to a humidistat? I'm wondering if even running a cheap room fan might move the air around enough to dry it out.

 

[RossABQ]

I think you are misunderstanding the concept of relative humidity. Warm air holds more water than cold. Making the room warmer without removing any moisture doesn't do a thing, although it does lower the RELATIVE humidity when you get up to 20+ deg C. You want to lower the ABSOLUTE humidity (lbs of water per lb of air). Exhausting would definitely help, but your energy costs will skyrocket unless you do heat recovery. Yes, you could hook it to a humidistat but they generally work at room temps, not so well at 5 deg C. Might be better to just cycle the system, based on how much moisture is coming off the car, snowblower, etc.

If the problem is mostly underslab moisture, ventilation will help deal with it, but getting to the source would be better ($$$$$$$$$$$)

 

[longshanks]

Ross, what do you mean when you say 'cycle the system'? I take this to mean keep running the heater. When it runs it uses mostly indoor (humid) air for combustion, and then vents outdoors.

If I understand what you are saying, getting to the source of the humidity would be pretty expensive? I am considering having a concrete company come and give me an estimate on sealing the concrete, and also providing an opinion about whether it would be worth it.

 

[trainer]

Another solution would be to install an air exchanger

 

[RossABQ]

Ross, what do you mean when you say 'cycle the system'? I take this to mean keep running the heater. When it runs it uses mostly indoor (humid) air for combustion, and then vents outdoors.

If I understand what you are saying, getting to the source of the humidity would be pretty expensive? I am considering having a concrete company come and give me an estimate on sealing the concrete, and also providing an opinion about whether it would be worth it.

I meant cycle an exhaust fan with heat exchanger, get rid of moist air and replace it with dry air. This would inevitably cause the heater to cycle as the heat exchanger is not 100% efficient, the garage would gradually lose heat, but much less than if you exhausted without an exchanger.

If the moisture is coming up from below, sealing won't stick.

Another solution would be to install an air exchanger

That's what I mean by an air-to-air heat exchanger. Warm moist air leaving the garage transfers its heat (but not moisture) to the incoming air. They are like a plate-and-frame heat exchanger.

Here's a good enough explanation: http://en.wikipedia.org/wiki/Heat_recovery_ventilation

 

[Titus]

It seems that most of your suggestions so far are directed at handling the symptoms of the problem, as opposed to the source of the problem.

I spent countless hours thinking about the cause of my humidity issue in my shop, followed by time and money buying and installing seals for the doors that had no affect. $100 and another hour more time and I had a dehumidifier with an outside drain purchased and installed, and I have not looked back in a year. Sometimes dealing with the symptoms of the problem is quicker and cheaper than finding and fixing the source.

 

[RossABQ]

......... Sometimes dealing with the symptoms of the problem is quicker and cheaper than finding and fixing the source.

Exactly (unfortunately) true, but there are some other things to consider. Do you have gutters on the garage, so that rain/melting snow coming off the roof is not going straight down along the edge of the slab? Is drainage on the site directing surface rain away from buildings? Water can't percolate up underneath the slab if there isn't any water to begin with (unless your water table is just under the slab). A drain system (gravel and french drains) around the perimeter may be useful.

 

[longshanks]

great ideas guys. Looks like I have some more light reading to do...

The garage has eaves on both sides and little moisture is getting under the slab, as far as I can see. There may be some drainage of water around the edges of the slab but short of digging it all up, I can't prevent that. It is built on top of very porous soil. Where the humidity is coming from is somewhat of a mystery to me.

So... a couple hundred for a humidifier -- I can live with that, but what would the cost of heat recovery ventilation for this structure be?


thanks to all for your input.

 

[djjsr]

So... a couple hundred for a humidifier -- I can live with that

Not a humidifier, a de-humidifier.

 

[bucs012]

Lots of good info here. Also keep in mind you may have to go to great lengths to deal with your issue depending upon the above factors AND if you are in a warm climate or cold climate.

 

[StingRay]

My garage gets very wet when we bring the vehicles in. We squeegee the water out and turn the the heat up to about 70 overnight with the dehumidifier running. That generally dries things up quite well. It takes longer when it's colder as the floor is colder and will not evaporate off very well. When necessary I add a fan to the problem areas and they will then dry up alot faster.

 

[longshanks]

thanks again all. I think I'll try adding a de-humidifier to the mix.

cheers

 

[Fubeca]

If the outside temp is significantly colder than the inside temp, just open all the doors for a few minutes and let all of the warm humid air out. Then heat the cold air from outside. The cold air has low humidity compared to the inside air and your inside air humidity will go down as the air heats up.

The energy cost re-heating the air is not at bad as you would think as the air has a very low specific heat and the slab and other interior components of the garage hold most of their heat.

This would at least let you know if an air exchanger would be beneficial. I do this periodically in the winter with my home as the HVAC system was poorly designed for ventilation.

 

[bucs012]

My garage is only heated when I spend a lot of time out there. She runs about 75-80 percent humidity this long winter! As I warm the air up when I am out there, the humidity level goes down to about 60.

 

[jamesemery728]

Have the same problem in the summer. High Georgia humidity in a basement. A dehumidifier is the way to go. I run mine all summer and it works like a charm.

 

[Phuckin' Jim]

I leave ours un-heated unless I'm in there. Also, I squeegee any water out. Humidity stays fairly high, but it hasn't been a problem. Sometimes if it gets too humid, I leave the big door open for 10 minutes or so, that dries it out pretty good.
24 x 24 garage, near Winnipeg.
I try to keep it @ -2C and the humidity seems to stay @ about 80%

 

[Daniel Dudley]

Go to the Radonseal website and check them out. Read the testimonys and see if any of it applies to your situation.

I sealed my floor, and since it was already prepped, I painted it. Also, bleach the mold on the walls or replace the rock. Reprime and paint with an anti mold paint like bathroom paint.

Also, the test for concrete is to tape down a 2'x2' sheet of plastic with duct tape all around the edge. If moisture forms under the sheet, there's your problem.

 

[peicraig]

I was having bad humidity problems in my garage the past winter. *backstory, newly built a 22'x26' attached garage in Dec.09 -- infloor heat and drain in the floor*

It's was terrible timing to build something in PEI, Canada as the temps were dropping, and I was trying to keep the heat up a bit to dry out the concrete walls and floor, so very high humidity resulted.

I installed a Whizzvent and it worked wonders. It's apparently the same power usage as keeping a 60w light bulb on (while the fan is running).http://www.wizzvent.com/

Within a week or 2 of install in Jan.2010, my moisture problems were gone. Now I can keep my garage at a steady 7deg celcuis, and have no moisture problems at all. snowy cars and all.

 

[dumper]

Also, the test for concrete is to tape down a 2'x2' sheet of plastic with duct tape all around the edge. If moisture forms under the sheet, there's your problem.

Bingo! Odds are you already know this is probably the problem. Do you have a high water table in your neighborhood? Any septic or leachfield issues? Stream in your backyard? I mention these things because I owned a house with all of the above, and the house had a curtain drain system set up to divert as much water away from the foundation as possible.