Dehumidifer in the garage

[QwikKota]

A few years back I insulated my garage walls and installed a window for a small air conditioner. It was nice for all of a month or 2 until the cost per kW/hr went up quite a bit and I replace the A/C with a basic box fan. This blows in humid air and makes for swampy conditions while working on vehicles or fabricating things. A friend recommended a dehumidifier and I eventually found one with integrated ports for ducts. It is intended for a hydroponics tent but I'm not into that sort of thing. Seems like a nice unit though.

My Wife gave me a window block off plate with port from her lab for the hot exhaust side and I let it run during the work day. It was a little drier in there when I got home but I was shocked how hot it was compared to outside. The garage is detached and the ceiling is only plywood, no insulation. The temp delta was at least 10 degrees. Humidity was around 65% to 70%, outside it was 85% or so.

I drilled and tapped a few holes in some aluminum plate after work and was still sweating but not quite as bad. I had a fan going but when I stepped back outside it felt a lot cooler. I don't want to return the dehumidifier (I can use it inside the house) but was curious if the is any benefit to using it in conjunction with the fan in the window? Most likely it would be overwhelmed as the fan flow rate is a good bit higher than the unit can keep up with.

 

[DogLover]

Is the dehumidifier bringing outside air in, dehumidifying it and exhausting it into the garage? Why not let it pull the air inside the garage and dehumidify it? No matter what, it is going to be hot without an AC. And a good AC would lower the humidity. But, as you noted, your electric bill will increase.

 

[JavierH19]

What btu's was the window AC and did you run it in low. Also you do know that dehumidifiers at least the ones that aren't junk are secretly window AC's under the skin except that they don't usually blow the hot air out but blow it inside so it consumes the same amount of electricity if not more than a window AC while also raising the temperature a lot which in turn makes the humidity worse since warmer air holds more moisture in the air than colder air which holds less moisture even when the percentage for both is the same.

Dehumidifiers with a duct to expel heat still aren't good since the condenser and motor generate heat and that heat dissipates into the air inside and not out the exhaust duct so they still raise the temp just not as badly as ones without an exhaust duct. Window AC's have the hot parts outside so their heat doesn't dissipate into the inside. Window ac's at least the undersized units or ones that can run slower than most are better at dehumidifying than dehumidifiers given that raising the temperature raises the amount of water the air can hold but cooling it lowers the water that can be held in the air.

 

[QwikKota]

The duct blows hot air outside. The intake is the air inside the garage.

I believe the window unit was around 8k btu. I think it pulled over 700 watts but I would have to verify. The dehumidifier is not moving much air and only pulls 240 watts. I had the window unit set to auto but it is an older unit and took a while to start cooling. It was given to me by my Father and we use it in emergencies after hurricanes when the power is out, hooked up to a generator.

 

[SC Maintenance]

A dehumidifier is beneficial but there is no free lunch. If you drop the humidity your still going to be less sticky but still just as hot, likely more because the dehumidifier gives off more heat.

Adding a fan will just bring the outside humidity back in. No point in having a dehumidifier in that case.

AC both cools and dehumidifies.

I have a portable AC in the garage runs at about 1000 watts. Electricity here is 14 cents kWh. 14 cents an hour to stay cool sounds good to me. How much is your electricity? I thought Texas was cheap?

 

[GaryMX5]

My limited experience with dehumidifiers (basement use) is that they are not really designed to move air like a fan or an AC unit. Venting the attic with a solar vent fan could help reduce heat build up in the garage.

 

[dbias]

A dehumidifier is beneficial but there is no free lunch. If you drop the humidity your still going to be less sticky but still just as hot, likely more because the dehumidifier gives off more heat.

AC both cools and dehumidifies.

I have a portable AC in the garage runs at about 1000 watts. Electricity here is 14 cents kWh. 14 cents an hour to stay cool sounds good to me. How much is your electricity? I thought Texas was cheap?

This^^^. My garage is attached to the house with three ducts feeding in from the main hvac from the house AND I have window unit to boost the cooling if needed. I want to be comfortable when I’m working on my cars no matter what. The money my DIY mechanically has saved me over 45 years certainly justifies being comfortable.

 

[Tdbo]

I'd say that if you are going to burn the electric to run a dehumidifier, you may as well run an A/C and get cool air along with the dehumidification.
How large is the A/C you have? How old is it? You may want to shop and see if you can get a more efficient unit.

 

[JavierH19]

The duct blows hot air outside. The intake is the air inside the garage.

I believe the window unit was around 8k btu. I think it pulled over 700 watts but I would have to verify. The dehumidifier is not moving much air and only pulls 240 watts. I had the window unit set to auto but it is an older unit and took a while to start cooling. It was given to me by my Father and we use it in emergencies after hurricanes when the power is out, hooked up to a generator.

Yeah the older units are not very efficient I believe my really old 5000 BTU I have in mexico is rated to draw 700 watts on the tag but that old built like a tank GE is nearing 20 years old by now and it's still going strong so I don't feel like retiring it. When I go there and turn it on she gets the cooling fast and stays on high until I leave for Texas which can be up to three days straight running on high with the thermostat at the cooling a room twice its rated size very well.

The inside is almost a hundres when I arrive during the summer days and it will bring it under 70 and maintain it during the summer afternoons down there. The home walls are made out of cinder blocks and the roofs are made out of concrete and rebar. They're literally just concrete boxes and rectangles but I believe it's a pretty decent insulator. I do check the window and door seals for air leaks regularly. I was told by the builder it's the most important thing for keeping cool and I believe it. Those doors and windows are a little bit hard to close because there's such a thick seal around them. But when they're closed i cannot feel a crack of cold air around any of the edges outside.

I remember reading somewhere that frigidair makes the most efficient 5000 BTU AC which draws around 300-350 watts. If we could relax some of these ridiculous regulations and could put R290 into these little window ACs the power draw would to drop by around 10-15% because of how efficient R290 is. But a lot of local codes don't allow for any A3-rated refrigerant in homes even if it's a teeny tiny little window ac system that would only 1-4oz depending on the btu size while you are fully allowed to have up to twenty 240oz/15lb of essentially unpurified r290 commonly known as propane tanks in many jurisdictions outside your home without a problem.

 

[QwikKota]

As mentioned, the hot air from the dehy is going outside. The heat is from the sun and ambient. Garage is detached so no shared insulated/cooled walls to take advantage of. The energy used by the dehy is less than half of a traditional window a/c unit. It's extremely quite and the air flow is very low. No lights dim when it comes on like my window unit.

I have an old furnace blower in the garage attic eves that helps but it's not on an automatic circuit and pulls in humid air from around the garage door.

I will look in to some of the newer, efficient window units as I already have a stout window sill I added and a 20 amp circuit I installed nearby.

 

[SC Maintenance]

As mentioned, the hot air from the dehy is going outside. The heat is from the sun and ambient. Garage is detached so no shared insulated/cooled walls to take advantage of. The energy used by the dehy is less than half of a traditional window a/c unit. It's extremely quite and the air flow is very low. No lights dim when it comes on like my window unit.

I have an old furnace blower in the garage attic eves that helps but it's not on an automatic circuit and pulls in humid air from around the garage door.

I will look in to some of the newer, efficient window units as I already have a stout window sill I added and a 20 amp circuit I installed nearby.

Honestly, how much are you possibly going to save buying a new AC unit? How much is your electricity kwh? How many watts does your AC pull? Its pulling the lights down due to motor surge at start - which for an AC can easily be double its actually running current.

You said it pulled 700W. I am actually guessing its closer to 1000W. If you ran it 10 hours that is 10kwH and if your energy is 20 cents kwh then you spent $2. If you ran it for 100 days thats $200.

If you buy a more efficient one that burns 800W, then your at $1.60 per day so over 100 days you save $40. A new AC is how much? ROI never pans out.

Stick your AC in the window. Keep working. $200 a summer isn't that much money.

 

[QwikKota]

We used to have quite affordable energy rates but they went up a few years ago. Currently paying 12.5 cents/kWh. That might sound cheap to some but it's all relative. It used to be closer to 10 cents. If I had 2 windows I could alternate between the open window with the fan and still have one dedicated to the a/c. It is a bit of a pain to swap out. Old unit is heavy even though 110v. I can check the current draw with my meter with the unit on low and see what it's actually doing.

 

[gfh77665]

I live in Baytown so I know. Window units are much more efficient than a generation ago. I would just run one and be comfortable.

 

[2010Civic]

First thing I would do is insulate the ceiling.

 

[QwikKota]

There was a vinyl enclosed insulation I had lined up but never pulled the trigger. It was white and would reflect light nicely while containing any fibers. The attic is already covered in OSB and I don't want to add any more weight on the underside. I need to check pricing again as it had a built in nailing flange to make install easier in the rafter bays. Same insulation used in a pole barns.