Options for removing garage humidity

[JasonF]

My situation is that I have a very well insulated 32x48 shop, scissor trussed with 12' sidewalls. Here in Michigan in the winter it holds heat well enough that it never gets below freezing even without running the furnace for weeks at a time. In the summer it's just opposite, it could be 90f outside but inside it won't get much above 70 if I keep the doors closed. My problem is that in the summer, even though it's a nice temperature inside the humidity is just too high. To the point I get fuzz on things like snowmobile covers, tackle bags and some tool handles.
Now I know opening the barn up and circulating air more would help but I would rather keep the hot air out and the cool working conditions inside. I then considered a dehumidifier but for the size I need I'm pretty sure it would heat the place up too much. The last option I've considered would be a window style air conditioner that has a dehumidify setting, I just don't know if this is best cause I don't need cooling on too many days.
I already run a couple large ceiling fans 24/7, these help some.
Are there any options that I'm just not considering?

 

[gizardlizard]

I live in Wisconsin and had the same issue. I ended up installing a cheap, ductless mini split. Best decision ever.

 

[Barnabas]

I run a dehumidifier in my garage. It sits on top of our full-sized freezer and the hose drips into a laundry room sink. There is no more heat coming off the back of the dehumidifier than would come off a refrigerator.

 

[bb29510]

open the door

 

[Metal-Marc]

ductless mini split

 

[toolmiser]

My parents had a garage that the floor would "sweat". It was insulated fairly well. They discovered in the summer to leave the hatch open to the attic and it would keep real dry. They made a screen for the hatch in case a bird got into the garage.

 

[charbar]

A smaller window A/C will act the same as a dehumidifier.

 

[JasonF]

So it looks like if I want to keep the place closed up I need to be looking at a mini-split, a dehumidifier or a window air conditioner. Hindsight being 20/20 I probably should have just done the mini-split from the start, instead of the hanging furnace, and I could have both seasons covered.

I run a dehumidifier in my garage. It sits on top of our full-sized freezer and the hose drips into a laundry room sink. There is no more heat coming off the back of the dehumidifier than would come off a refrigerator.

Interesting, I had a small one in my basement and although it was a older unit, it put out a ton of heat. I'll have to check into this more.

 

[finn]

Mini split, and run it in the dehumidify mode.

Your problem is that the inside temperature is below the dew point. Opening the doors will let more warm moist air in, and you’ll have high humidity and condensation until mid summer.

i have the same issue, except in the shop where I have heated floors. The insulated slab never gets cold enough to cause the spring humidity problem my other garage has. Thinking about it, a thick, high mass unheated, uninsulated slab is probably worse than an insulated 4” slab too.

 

[JasonF]

Thanks for all the replies. Any idea what size mini split I should be looking at for my barn which is well insulated at 1536sqft with 12' sidewalls and scissor trusses (so ~14.5'h at the peak)? From doing a little digging on older posts here it looks like it's more critical to make sure the unit is not oversized.

 

[OX1]

Is moisture coming through your slab?

Concrete Moisture Problems - Concrete Network

Information on the problems that excess moisture in concrete can create.

www.concretenetwork.com

I wasn't sure if it really happened or not, but I spent big money on a "pool liner" thickness barrier
that was compatible with concrete, just in case. I know you can't do this now, but for others in the future.
But you might be able to do some coating to restrict it, if you don't have anything now.

I've had an early bronco on my 2 post just sitting for 6-7 years now, it has some sanded areas that were
never primed and they are still shiny. I have a 3 way remote temp/humidity guage setup with sensors outside,
in pole barn, and up in trusses of pole barn. Don't think barn has ever been over 68%, and that is only when
it 100% outside. Usually it is the mid-high 50's.

I do have 2" sprayed insulation now, but it does not do as good a job as you describe controlling temps.
I did it more to keep the steel panels from "moisture welting".....

 

[JasonF]

Is moisture coming through your slab?

Don't think that's the case, similiar to you before my pour I laid a solid sheet of Stego liner, 10mil I think.

 

[OX1]

Don't think that's the case, similiar to you before my pour I laid a solid sheet of Stego liner, 10mil I think.

Good deal, didn't even know they make them solid.

Would a more industrial "leaning" dehumidifier use less power than an AC system, since you don't really need temp control?

 

[beemerphile]

Good deal, didn't even know they make them solid.

Would a more industrial "leaning" dehumidifier use less power than an AC system, since you don't really need temp control?

Minisplits can operate in a "dry" or "dehumidify" mode and are very energy efficient. You add the benefit of being able to temper the temperature up or down if the odd day comes that you need it. Even without dry mode, you don't have to worry about oversizing quite as much with a mini split as you do with regular units because they have better turndown ratios.

 

[CraigStu]

Be sure to check the dehumidify function of any ac you install. I put a window unit in a hole I cut in the wall in my garage. What I realized later was there is no drain hole in the outside of the unit. I have no idea how it works but assume there is some system like a frig or freezer has to get rid of condensate.

 

[racecougar]

Be sure to check the dehumidify function of any ac you install. I put a window unit in a hole I cut in the wall in my garage. What I realized later was there is no drain hole in the outside of the unit. I have no idea how it works but assume there is some system like a frig or freezer has to get rid of condensate.

A lot of window units use a "slinger ring" on the fan to throw the water from the drain pan onto the condenser.

 

[BombShelter]

Old thread but these keep popping up on the bottom. Please do not open doors and windows, that's how the warm moisture-laiden air gets inside and condenses on the colder tools and floor. Ideally it's buttoned up really well so there's very little air transfer from the inside and outside. I've got a slab on grade home north of there that the caretaker loves to "open" up with spring. When I visit, everything is coated with moisture, no amount of reasoning will change their mind about their approach.

You can try to reach temperature equalibrium by using fans and heat but most people like the shop colder if they're doing a lot of work. Personally I use a dehumidifier and it pulls a ****-load of water out of the air, I can tell when it's done working, when the floor doesn't look dark and wet.

For future slab on grade builders reading this, I'd use CETCO Voltex, it can be rolled under the concrete before pouring. It has an outer layer of plastic, then a cottony fabric holding bentonite powder with parts of the fabric sticking up. When the concrete is poured, the fibers bond with it. No water will ever move through this barrier if installed correctly.

VOLTEX Waterproofing Membranes | Minerals Technologies Inc.

VOLTEX waterproofing membranes combine the power of sodium bentonite within a durable geomembrane to provide waterproofing protection for any cast-in-place, below-grade concrete construction.

www.mineralstech.com

 

[smackey05]

Minisplit, rolling AC, or window AC unit to remove the humidity.

I'm running the rolling AC as a solution for the summers only. I'd do the mini split, but there isn't a place to add it that wouldn't make the exterior of my house look ugly...

 

[MovingAlong]

Unlike a mini-split or window ac, a dehumidifier doesn't always get ducted to the outside. In a basement that would be tough, in the garage it might take a bit of sheetmetal work but doable.

You'd be amazed at the difference a $100 window ac rated for 100sf can make in 500sf! Yes, it will run it's little heart out but I've had them still last for many years. (I know, nobody sells a $100 unit anymore. Concept still applies...)

 

[MovingAlong]

Minisplit, rolling AC, or window AC unit to remove the humidity.

I'm running the rolling AC as a solution for the summers only. I'd do the mini split, but there isn't a place to add it that wouldn't make the exterior of my house look ugly...

A cooled garage would never look ugly to me!

 

[Sumboodie]

HRV unit.

 

[Kpaige]

A big thing is how well is your slab insulated? Is there a vapor barrier under the slab?
I recently had my old garage lifted it’s old enough never had any insulation etc under slab now with all the spray foam the air does not condensate in the garage.

 

[crazylunker]

Be sure to check the dehumidify function of any ac you install. I put a window unit in a hole I cut in the wall in my garage. What I realized later was there is no drain hole in the outside of the unit. I have no idea how it works but assume there is some system like a frig or freezer has to get rid of condensate.

the newer thruwall/window units don't have drains like the old ones, they have a well below the condenser fan with the thought that it helps cool the the condenser coil aiding in efficiency. I drill a hole in the bottom of the units just below the outside fanblade to let it drain. Every since doing that the room feels much drier (not a fan of humidity) and it shows on my humidistat as well. I haven't noticed an increase in electrical use either.

 

[CraigStu]

crazylunker, thank you, I will look at mine to figure where to drill a hole.

 

[finn]

Don't think that's the case, similiar to you before my pour I laid a solid sheet of Stego liner, 10mil I think.

I had a floor poured in the unheated lean to off my shop a few years ago, and fully enclosed it by adding a garage door on the previously opened end.

I didn’t add a vapor barrier, and see no signs of moisture or any other ill effects. The site is well drained, and very sandy, and the room is not heated or insulated, except the 60’ wall adjoining the shop and the 16’ wall adjoining the office / bathroom. Most importantly, the door is mostly closed in the spring, when I would get significant condensation on a different garage.

I am pretty sure a vapor barrier must be installed by code for a heated building, but not for an unheated building.

I hear talk about moisture coming through the slab, but I don’t see it happening if drainage is proper. I get more moisture from the stupid leaky metal roof after a rainstorm than anything else. Might be a different story if the door was open in spring, but intrusion by squirrels and chipmunk necessitates keeping the door shut whenever possible.

 

[Imatk]

As many have posted. Get a mini split. That's my favorite... FAVORITE thing in my garage.