Looking for advice... Hotlanta garage

[AirCooledTiger]

Hi, folks -

Been a member for a while and learned quite a bit from this forum.

I'm looking for some advice on how to address the miserable heat/humidity in my garage. I enjoy working on my cars and it is just miserable in July and August.

It's a basic 2-door, 2-car garage in the Atlanta area. Approximately 420 sq ft. 11' ceilings. Garage faces 9º N. There is a half-glass man door to the outside and a window -- both on the east side. There is a good bit of morning shade. North side is brick. East side is hardie board siding. Second story above garage is heated/cooled.

All the lighting in the garage is LED but I do have a refrigerator (the beer fridge) that is a heat source. Of course if the cars have been driven and parked they will be heat sources as well.

I took some measurements yesterday. The outside high was 88ºF and the low was 74ºF. Over that 24 hour period the high in the garage was 88º and the low was 81º. The high humidity was 65% and the low was 53%.

A couple of years ago I replaced the garage doors. The new ones seem to be much better insulated than the old ones -- I suspect they might be contributing to trapping heat inside. Last night when the low was 74º outside the outside face of the garage door was also 74º. The ambient air temp in the garage at the same time was 88º and the inside of the garage door was also 88º -- a 14º temp difference!

Even with the doors up in the evening and fans running it seems that the garage just stays heat soaked. I don't think I really understand which factors are contributing the most to the heat soak though.

Option 1: Window film

I've thought about having 3M Crystalline film applied to the glass in the garage. That would help reduce UV heat from coming in but I'm not sure how much that is really contributing to my problem.

Option 2: Vents & Suction Fans

I've seen where some people install suction vents & fans. I was thinking if I could install vents in one end and a wall mounted suction fan on the other that would help pull air through the garage.

Option 3: Split A/C or heat pump

I don't think I can get away with a window A/C unit. Wife and HoA would likely disapprove and plus the window is ground level so it might be a security risk. I might be able to install a window unit on the back wall though.

I've also looked at things like the Mr Cool DIY. That seems more do-able.

My question is with wife and kids coming/going all the time, won't I lose a lot of cooling from this type of approach with the garage door going up & down?

The pro of a heat pump type unit would be that it would make the garage more comfortable in some of the winter months.

Obviously the extra benefit of an A/C unit will be reducing humidity as well.

I have a sub-panel in the garage with a 30A breaker that could support either 110 or 220. My plan was to save it for a lift or air compressor one day. Maybe I could figure out a way to switch it where only one thing was active at a time.

Option 4: Dehumidifier

This might help in the summer months just to knock down the humidity.

Any other ideas? How are some of you solving this problem?

Opinions on which approach(es) will be the most effective bang for the buck?

I'd really appreciate any/all feedback.

 

[EdT]

No matter how you cool the space, when the door is opened all the cold air will "fall" out the bottom of the opening sucking in warm air behind it at the top of the opening so that air will have to be cooled and de humidified again. There are a lot of variables at play here, but is there any potential in tapping into the HVAC supply for the conditioned space above the garage preferably with some way to not do that when you're not working in the garage. I am guessing that the south and west walls are attached to the house. Any possibility in stealing some AC from the first floor?

 

[Shiftless]

No matter how you cool the space, when the door is opened all the cold air will "fall" out the bottom of the opening sucking in warm air behind it at the top of the opening so that air will have to be cooled and de humidified again. There are a lot of variables at play here, but is there any potential in tapping into the HVAC supply for the conditioned space above the garage preferably with some way to not do that when you're not working in the garage. I am guessing that the south and west walls are attached to the house. Any possibility in stealing some AC from the first floor?

I don't think fire codes will let you do that. Also, the return air to the house will bring in fumes from the garage.

 

[AirCooledTiger]

I don't think fire codes will let you do that. Also, the return air to the house will bring in fumes from the garage.

I think you're right about fire codes and fumes. Doubt I could get that to work anyway. Might be able to get a duct but there is no return.

 

[txst]

Please DO NOT tap int your main system for the house. That's against code for a reason - Your familys lives are at stake.

 

[AirCooledTiger]

Another data point. Right now it's a sunny day. At 1pm the weather outside is 84°. Inside the garage is 84° and the humidity is 56%. I've got a wall fan that has been running since this morning.

Would a vent mounted low to the ground on the end with the garage doors and a suction fan mounted high on the other end wall help? I'm thinking about the principle of how a whole house fan works.

 

[AirCooledTiger]

Please DO NOT tap int your main system for the house. That's against code for a reason - Your familys lives are at stake.

I think my wife would kill me the first time I sprayed brake cleaner in the garage and the smell was sucked into the house.

Not to worry. I won't go that route.

 

[Jinks]

Do the Mr. Cool DIY! I have a Mitsubishi 12K mini-split in my garage/shop of about the same footage. First, it'll cool & dehumidify your space all you'll need to make it comfortable to work in. Secondly, opening & closing the garage door doesn't make anywhere the difference people think. Parking a hot car in the garage makes some difference, but not enough to prevent working there.

I can sit in my garage & watch boat traffic on the intracoastal waterway. I have, when the humidity was bad enough, ran the A/C with the garage door open. It took less than a half hour to cool & dry the shop. On a normal day I'll use the mini-split while working in the shop, going in & out the garage door as needed but closing it each time. The shop stays cool. In the evenings when the outside temp reaches the mid 80's the wife & I take a couple of adult beverages into the shop. We turn off the mini-split, open the garage door, sit & watch the traffic. All in cool, dry comfort. We can count on at least an hour before the temperatures equalize, & longer before the humidity inside rises to outside levels.

When my 3 or 4 year old Mitsubishi dies I'm going to replace it with a MR. COOL DIY. I'll do a better installation then the "professionals" that did this one......

 

[DC73]

My question is with wife and kids coming/going all the time, won't I lose a lot of cooling from this type of approach with the garage door going up & down

It's not that bad as long as you don't leave the doors open for extended periods. Research the concept of "thermal mass". Basically, once you get all of the concrete, walls, etc to the set point temperature, they don't warm up very fast when the door is open so all you are having to do is re-cool what air escapes.

Go for it.

DC

 

[Shiftless]

Another data point. Right now it's a sunny day. At 1pm the weather outside is 84°. Inside the garage is 84° and the humidity is 56%. I've got a wall fan that has been running since this morning.

Would a vent mounted low to the ground on the end with the garage doors and a suction fan mounted high on the other end wall help? I'm thinking about the principle of how a whole house fan works.

I live in a much milder climate but I did install a whole house fan to pull in the cooler night air and flush out the overheated attic air.
Obviously with that you won't get the inside any cooler than the outside but with a breeze flowing though the house you will feel a bit more comfortable compared to sitting in still air
I have a 2000 sq. ft. house and my 2 speed fan pulls 8000cfm on high and about half of that set on low.
Make sure to install a high temperature kill switch or smoke detector or ??? if you go that route. If a fire gets started the whole house fan will greatly accelerate the spread.
I also wired mine with a timer switch so nobody can leave it on all night.

 

[Marctrees]

Why would you need a split AC or heat pump in Atlanta?

Get a 15k window AC, mount it throughwall, and be done for $500.

Read other current posts about this in this subforum, in fact right on the first page.

And of course when not running the AC, static or powered venting would be good, specially outside of worst summer heat. Marc

 

[mpire]

If you have a water heater in the garage then get a heat pump water heater instead of a dehumidifier.

It will save you money on hot water and it will do a great job of removing the humidity from the air.

Power companies are giving large incentives to go with a heat pump water heater.

 

[AirCooledTiger]

Appreciate the feedback.

The reason I have leaned towards the split and not a wall-mounted window unit has to do with space. Doubt I can put the window unit on the east side because it would be visible from the street. Wife/HoA. If I can figure out a way to hide it I might be able to go that route. Maybe strategically placed shrubs. It would have to go in the window -- no space on that wall. That's valuable tool & storage space.

The south wall only has about half the wall open to the outside. Need to take some measurements of window units and the Mr Cool unit to see what could fit. It would have to mount high on the wall above tool storage.

I found a window fan on Amazon for ~$50 that is reversible and has a temp setting. I thought it was worth a shot to do a little experiment to see if I raise the garage door an inch and get the fan sucking air through what kind of difference it will make. If it doesn't help I can always return it. Maybe it will buy me some time while I do some research on window units and splits.

 

[AirCooledTiger]

If you have a water heater in the garage then get a heat pump water heater instead of a dehumidifier.

It will save you money on hot water and it will do a great job of removing the humidity from the air.

Power companies are giving large incentives to go with a heat pump water heater.

Unfortunately my water heater is in the basement. I have never heard about a heat pump water heater. I have to run a dehumidifier in the basement so that would be great. Too bad I just replaced it a couple of years ago. That would've been good to know.

 

[mharris2007]

Do the Mr. Cool DIY! I have a Mitsubishi 12K mini-split in my garage/shop of about the same footage. First, it'll cool & dehumidify your space all you'll need to make it comfortable to work in. Secondly, opening & closing the garage door doesn't make anywhere the difference people think. Parking a hot car in the garage makes some difference, but not enough to prevent working there.

I can sit in my garage & watch boat traffic on the intracoastal waterway. I have, when the humidity was bad enough, ran the A/C with the garage door open. It took less than a half hour to cool & dry the shop. On a normal day I'll use the mini-split while working in the shop, going in & out the garage door as needed but closing it each time. The shop stays cool. In the evenings when the outside temp reaches the mid 80's the wife & I take a couple of adult beverages into the shop. We turn off the mini-split, open the garage door, sit & watch the traffic. All in cool, dry comfort. We can count on at least an hour before the temperatures equalize, & longer before the humidity inside rises to outside levels.

When my 3 or 4 year old Mitsubishi dies I'm going to replace it with a MR. COOL DIY. I'll do a better installation then the "professionals" that did this one......

I'm with Jinks. Mini split for sure. I have a 505 sq foot garage that faces east. The high at my house yesterday was 82 and the high in the garage gets to 88!! When I open the garage it doesn't heat the garage very much at all. Like another responder said, if the thermal mass is cool opening the garage does much less. I used a blue ridge mini split because I didn't want extra line set coiled up making an oil trap. Not sure if in real life that matters but I didn't want to be doing all this twice. I used a 15000 BTU version, but would recommend even bigger if you want it to cool fast and you have hot cars in there since the mini splits have an inverter. To me the hot cars are what heat the garage the most. I have a an E90 M3 and my wife drives an X5. Good luck.

 

[Theruse]

I find the dehumidifier makes a big difference.By bringing down the humidity from the high 80s -90s to 35% makes a big difference in comfort level.I will look at my dehumidifier and it will say 82 degrees and 35% humidity but feels more like 72 degrees. I try to limit leaving the garage door open. One issue with dehumidifier is that it is a heat source, so be mindful of that effect. In the summer, I leave the hot cars in the driveway until we go to bed, just so they cool down. I wish garage door makers offered the option for windows to be hinged with a screen, so you can have the protection of a garage door with the ventilation to let hot air out at night.

 

[Theruse]

I find the dehumidifier makes a big difference.By bringing down the humidity from the high 80s -90s to 35% makes a big difference in comfort level.I will look at my dehumidifier and it will say 82 degrees and 35% humidity but feels more like 72 degrees. I try to limit leaving the garage door open. One issue with dehumidifier is that it is a heat source, so be mindful of that effect. In the summer, I leave the hot cars in the driveway until we go to bed, just so they cool down. I wish garage door makers offered the option for windows to be hinged with a screen, so you can have the protection of a garage door with the ventilation to let hot air out at night.

 

[LS6 Tommy]

Option 5-
Move the garage North...

 

[Slednut]

I have an attached garage that's around 56x26, I have a window AC unit that does well but when the wife drives in the temp would go up a couple degrees. I installed a tarp that's suspended on a cable that I pull across between the work area and where the cars are parked. There's around 2 feet it doesn't cover but it still makes a big difference.

 

[lieutenant]

Slednut, that's a good idea. Nice garage too!

 

[Joe Reed]

I wonder why your garage stays so hot? Is it warm in the winter too?

Reason I ask is that my garage is the same size as yours, except with 9' ceilings. My door (insulated) faces west into the afternoon sun. the exterior north and south walls are brick (non-insulated). The east wall is attached to the house (insulated, of course) with a man door into the house. No man doors to the outside. Ceiling isn't insulated - and it's attic above.

You'd think mine would be hotter than yours with the uninsulated ceiling and west facing double door, but it's always a bit cooler inside than the outdoor temp, and a bit warmer in the winter. There is a freezer in there, but nothing else is powered up unless I'm working in there.

IMHO, a window unit (heat & cool) through the wall is the best bang for the buck in a typical subdivision garage like ours - in spite of the fact that I started a thread today about my unit quitting. Hopefully I can fix it for about $30. Regardless of the outside temp, I can turn it on high for 30 minutes and it gets comfortable enough to go out and start work. In an hour, I'm cutting it back to a lower setting.

I installed mine high on the wall...it was easier that way since I had to go through brick. It's on a side of the house where it doesn't cause any HOA problems. It cost about $600 plus a few bucks for outlet, breaker & wire. I installed it and did the wiring myself....the unit is only about 5 feet from the main breaker panel so it was simple.

Here's a couple of pics...

 

[AirCooledTiger]

Appreciate all the comments. I'll try to respond to all.

Joe, your question is exactly what has me puzzled. It's currently 8:40pm. Outside air temp is 79°. We had a brief shower so the humidity is up. It's 90° in the garage with 64% humidity.

Whatever heat is coming into the garage is staying. Heat soak. Something seems strange. Heat is becoming trapped. I do think the new garage doors are much better insulated. I think the winter garage temps are warmer than they used to be.

I'd like to figure out if there is something else contributing to the problem.

Some thoughts:

How much heat is the refrigerator giving off? Is it possible it is not running efficiently and giving off more heat? I don't know how to test this theory.

Cars. Only one car has moved today. I think it's been out 3 times. How would one begin to estimate it's contribution? No idea.

UV heat coming through the glass. My gut says this is not the problem but I suppose it could be.

 

[Joe Reed]

Unless the refrigerator compressor is running excessively, I don't think that would be an issue. My freezer doesn't create a problem....and my ceiling is 2' lower than yours, so fewer cubic feet of garage space.

Can you try covering the glass to see if that makes much of a difference? If you have much glass and the sun hits it directly, that'll certainly cause a lot of heat gain (think about your car in the sun with the windows up). That's one reason I ordered my garage door with no windows....instead of glass on the top row it's a fully insulated panel just like the others. The original garage door wasn't insulated and had the row of glass at the top....and the heat gain with the afternoon sun was huge.

 

[Joe Reed]

It's 86 here and humid (heat index is 95). It's 86 in the garage now as well, but the door was open for a bit...and my wife hasn't been home long, so her car is still pretty warm.

 

[AirCooledTiger]

Here's a pic of the garage. The door and window are covered with blinds and they are always closed.

You can see the window fan that came today. It got here this evening. Around 8pm I installed it. The temp in the garage was 90° and 60% humidity. It was 79° outside. I set the fans to intake to pull the cooler outside air inside.

About two hours later it was 88° inside and 66% humidity (probably because of some intermittent showers).

The unit has two 9" fans. CFM is not listed on any spec but I can't believe it's too high because they are pretty quiet. I also have an 18" wall fan running. I'm going to let them run overnight and see what, if any, difference there is in the morning.

I know this really isn't a long term solution. I'm just wondering if I can get the garage temps to at least equalize to outside ambient temps.

A good next step would be to cover the glass as you suggested and see what impact that has. If it does then the film might yield some benefit.

 

[AirCooledTiger]

Fans ran all night. At 8am this morning, the temp in the garage is 82° and the humidity is 70%. Outside temp is 74°. :-/

 

[Joe Reed]

80 degrees here - both outside and in the garage (I think the low last night was about 75). This is in a closed garage with no fans or other ventilation.

Try running your fans the other direction to exhaust the hot air, and maybe leave one door open an inch or two to allow a place for replacement air to come in.

 

[6768rogues]

In a warm climate, you can put a heat pump water heater in your garage. It will make hot water efficiently and the byproduct is cold air. The more hot water you use, the more cold air for the garage. The hotter the garage, the better the water heater works. Not huge quantities of cold air, but every bit helps and it is otherwise a wasted byproduct.

 

[cajunfirehawk]

FWIW, my house attached 2 car garage is similar to yours, maybe 18'w x 20'l, high ceilings, 2 windows that face the sun after noon, and the garage door is uninsulated, it too faces the sun in the afternoon. My ceilings and walls are sheetrocked but like most spec houses, neither the wall (afaik) or ceiling is insulated. I had my garage door tinted with limo tint to keep the sun out and my windows have blinds on them and one is blocked by a 6ft bush, that window has a small window a/c unit in it. I don't know the size of the a/c off hand but it was about $200 at the orange box store one summer on clearance. I leave it set on a setting that basically keeps the humidity down and the temp is set on 79 degrees and it cycles regularly. That setting keeps my garage in the 80's during the heat of our gulf coast days, but the humidity is about half of outside which in turn makes it feel much better. If I work on a car in there, I turn the a/c unit to high fan speed and that drops the temp some what, a small hi output fan helps the air circulate. It really is fine like this, but I am always trying to insulate my garage door and want to do my ceilings and I would imagine that would make a big difference. This garage is so much better to work in during the summer than my 30x40 uninsulated metal shop that it is no comparison, during the heat of the day, my closed up my metal building gets to 115!
YMMV, stay cool

 

[Joe Reed]

At 1:00 it's 93 degrees & sunny here and it's still 80 inside my garage, which has been closed all morning....so no heat gain at all halfway through the day. I'm sure it'll get warmer later in the afternoon after the sun beats on the garage door for a few hours.

I'm still baffled as to why your situation is worse than mine. You have air conditioned living space above your garage ceiling. I have no insulation and it must be 120 degrees in the attic above.

cajunfirehawk: If you haven't already put insulation on your door, you might try that Reflectix aluminum foil bubble wrap. It's cheap, easy to cut and install...and light enough that it won't be a problem for your opener & springs. Before I bought my insulated door I put that on my plain metal door. It made a significant difference. Before, the inside of the door was hot to the touch in the afternoon. After, the Reflectix wasn't even warm to the touch. Getting rid of that 16' x 7' radiant heater made a big difference!

 

[AirCooledTiger]

So the window fan was a miserable failure. Tried sucking in colder outside air and blowing out hot air. Tried opening the garage door an inch and the fan on exhaust. I don't think it had enough CFM to do much. I put it back in the box and will return it.

I went to HD and bought a 10k BTU portable where the exhaust port goes in the window. It's been running for about 4 hours. The garage is definitely more bearable. It's knocked the humidity down from the 60s to 49%. I've had cars coming and going and I plugged it in during the hottest part of the day so I'll see how it does overnight. If it can just keep it down to bearable I'll be happy.

Joe, I still do not understand it but my garage is like a greenhouse. Heat comes in and it never leaves. I think I'll start referring to it as Hotel California.

I may end up having to go to 12k or 15k BTU but this 10k LG was the largest BTU at the local store.

 

[rsanter]

It would help if you fans that would come on only when the outside air is cooler. That would economically remove head from that space most of the time.
Other times when you are working on there you can have an AC system that will cool the area for you to work

Bob

 

[Joe Reed]

I think the high here today was in the low 90s...it's 87 now. It's 81 in the garage.....so it only gained 1 degree all day...but it was partly cloudy this afternoon.

Is your garage situated over a volcanic magma chamber?

I had a cheap 10k portable in my garage for a year or so. When I planned to work in the garage, I'd sometimes let it run at night so the garage would be cool in the morning. If I let the garage get hot first it would help, but wouldn't get it really cool. It was certainly better than nothing. The biggest problem with it was that if I opened the double garage door to move cars in and out it wasn't very good at recovering. Hopefully you'll have better success with it. At least you have two doors, so maybe less loss of cold air when you do have to open one...

 

[d.swanson]

Have you tried experimenting with leaving the cars outside for a couple of days and see how much heat gain you have without the hot cars being parked inside?

 

[AirCooledTiger]

I think the high here today was in the low 90s...it's 87 now. It's 81 in the garage.....so it only gained 1 degree all day...but it was partly cloudy this afternoon.

Is your garage situated over a volcanic magma chamber?

I had a cheap 10k portable in my garage for a year or so. When I planned to work in the garage, I'd sometimes let it run at night so the garage would be cool in the morning. If I let the garage get hot first it would help, but wouldn't get it really cool. It was certainly better than nothing. The biggest problem with it was that if I opened the double garage door to move cars in and out it wasn't very good at recovering. Hopefully you'll have better success with it. At least you have two doors, so maybe less loss of cold air when you do have to open one...

While I have, on occasion, momentarily believed that I must be in hell, I don't think that is my problem. But who knows?

I got a cheap pyrometer. There were no obvious hot spots on the walls or ceilings. When I pointed it at the floor right at the base of the refrigerator I measured 95° temps. It has to be the refrigerator.

The 911 hasn't moved in days. I really don't think the other car is contributing that much. Rain came through tonight. It's now 72° outside at 11pm. I'm leaving the A/C unit running overnight. If it is not in the 70s in the morning then the refrigerator is the culprit.

 

[Joe Reed]

That certainly doesn't sound right. The floors next to my refrigerator in the house and the freezer in the garage aren't even warm....no discernible difference from the rest of the floor.

 

[Dragfluid]

Finally, after 2 pages of this, someone finally brought up something similar to what I was going to post, and that is:
CAN'T THE CARS BE PARKED OUTSIDE DURING THE DAY??

It really can't be that difficult for the wife to use the front door once in a while, can it? It's called cooperation. On the days that you're going to be out there for any length of time, park them outside and close the doors. Then fire up your mini-split that you have to have because the HOA's (long O) get their ******* in a twist over a window unit. Enjoy the cool, dry air.
Park the cars back inside at the end of the day.

Seem pretty simple.

 

[AirCooledTiger]

Finally, after 2 pages of this, someone finally brought up something similar to what I was going to post, and that is:
CAN'T THE CARS BE PARKED OUTSIDE DURING THE DAY??

It really can't be that difficult for the wife to use the front door once in a while, can it? It's called cooperation. On the days that you're going to be out there for any length of time, park them outside and close the doors. Then fire up your mini-split that you have to have because the HOA's (long O) get their ******* in a twist over a window unit. Enjoy the cool, dry air.
Park the cars back inside at the end of the day.

Seem pretty simple.

It's not the cars. Garage is hotter than outside even when the cars have not been driven.

10k unit is never cycling off. Don't think it's big enough. May have to go 15k.

The real heat source appears to be the fridge. Needs further investigation.

 

[d.swanson]

I think your garage is probably typical - For comparison, I’m in central NC (not quite as hot but probably just as humid) and my attached garage is 400-440 sf. The double door faces south. The adjoining wall is east, back wall north and the side wall is west. There is a finished bonus room above. The outside garage walls are R13 and the double door has one layer of ½” foam insulation with reflective surface facing out. Currently the garage is just automotive storage and the only appliance running out there is an old dehumidifier that pulls about a gallon a day and keeps the humidity around 50-55%. Yesterday our high outside was 92-93 and in the garage was 85 on wall adjoining the house and 87 on the west all. Overnight the low was 74 and in the garage was 81 on the adjoining wall and 83 on the west wall. Also, slab temperature was 81 (using a laser thermometer). If I was to open the garage door during the heat of the day or park hot cars inside, I would expect the temps to be much higher.

 

[James-W]

I have a window unit and it keeps my garage really nice in the Summer months. As far as security, if you have the window unit mounted right, it would be difficult to break in without making a lot of noise. I would have to say that unless you live in a "high crime" area you won't have an issue with a really well mounted window unit.