Metal Building AC Sizing 40x40 TX

[Mojaverider]

I'm working on a 40x40x14 metal building as a garage/car shop, and I'm looking for input on AC sizing. It is insulated with 2" of closed cell spray foam, has 6 windows, and is located in Central TX (hot, sunny, and humid). I've run some online calculators, and I'm getting results anywhere from 3.5 ton to nearly 5 ton. I was planning on a mini-split system, though 5 ton mini splits are few and far between, but I'm open to other systems as well.

I don't plan to run the system all the time, but to turn it on in the morning of days I expect to be out there all day.

Anything specific to pay attention to? Thanks!

 

[shade]

Multiple mini splits to achieve your desired load

 

[Mojaverider]

Multiple mini splits to achieve your desired load

Like 2 24k or 2 36k? Any particular reason to run multiple smaller units vs a bigger mini split vs a ducted unit?

 

[Yankeefarmer]

At 40x40 I’d be doing a central ducted split system. Just one thermostat for the big space, minimal ductwork to ensure good distribution, and, if it’s going to be a workspace, filter cleaning and maintenance will be simpler than cleaning multiple ductless heads.

 

[Mojaverider]

At 40x40 I’d be doing a central ducted split system. Just one thermostat for the big space, minimal ductwork to ensure good distribution, and, if it’s going to be a workspace, filter cleaning and maintenance will be simpler than cleaning multiple ductless heads.

I talked to one local HVAC contractor and they recommended a 3 ton central system, which seemed smaller that I would have guessed. Thanks for the input!

 

[karoc]

With your high ceilings I would go up, as I also do to figure an estimate on size is 1 ton per 600 sq ft. which is for 8' ceiling. It also being a metal bldg will also influence the size. But I agree I would consider a split household system instead of mini. I would suggest a package unit which mounted on walk which up at top cut in supply and lower you would cut in your return. Or you could run duct for your supply.

 

[Mojaverider]

With your high ceilings I would go up, as I also do to figure an estimate on size is 1 ton per 600 sq ft. which is for 8' ceiling. It also being a metal bldg will also influence the size. But I agree I would consider a split household system instead of mini. I would suggest a package unit which mounted on walk which up at top cut in supply and lower you would cut in your return. Or you could run duct for your supply.

First HVAC contractor I talked to quoted me a 3 ton unit, but stepping up to a 3.5 or 4 doesn't seem like an awful idea with the high ceilings and big doors.

 

[Hobby_Man22]

I have a 5 ton on a 30x50x12 and it will only do like 74 when it's like 90 outside, so if you want to keep it like a meat locker I'd go bigger.

I have two 10x10 uninsulated steel doors, so I guess that makes a difference, although they do have seals on them.

 

[Mojaverider]

I have a 5 ton on a 30x50x12 and it will only do like 74 when it's like 90 outside, so if you want to keep it like a meat locker I'd go bigger.

I have two 10x10 uninsulated steel doors, so I guess that makes a difference, although they do have seals on them.

I'm not aiming for meat locker, but I've got 3 total uninsulated doors: two 10x10 and one 12x12. Thanks for the data point!

 

[Hobby_Man22]

It basically runs constantly from say 1:30pm-5pm I have R30 on the roof and did R30 on the sides. Maybe one day I'll go back and add more like R15 to the R30 but i'm not really in the mood to do that anytime soon. lol

 

[Hobby_Man22]

I left it on for a month, but turned up to like 82 when I wasn't in there and the bill was only like $65 but for some reason the they're only charging me like 3.5 cents per kwh plus delivery charges. It used like 800 kwh that month. I wasn't going to ask why it was so cheap. lol

 

[Mojaverider]

I left it on for a month, but turned up to like 82 when I wasn't in there and the bill was only like $65 but for some reason the they're only charging me like 3.5 cents per kwh plus delivery charges. It used like 800 kwh that month. I wasn't going to ask why it was so cheap. lol

I don't expect to run it all day every day, at least while I have a day job. Planned usage is expect long wrenching days, so kick it on in the am and let it run at most all weekend. Also thinking I need a wifi theromstat so I can adjust the time from inside the house and not have to go out there.

 

[Boosted73Z]

I don't expect to run it all day every day, at least while I have a day job. Planned usage is expect long wrenching days, so kick it on in the am and let it run at most all weekend. Also thinking I need a wifi theromstat so I can adjust the time from inside the house and not have to go out there.

I also have a 40x40x14 metal building I’m looking to add ac, checking to see if you made a decision and how it’s working out for you?

 

[My Old Tools]

My metal building is 30x40x12 with a 6/12 open to roof, 22 feet tall. I have 7 3x5 double pane windows, walk door, and 12x12 insulated overhead door. Insulation is conventional plastic backed fiberglass roll. It is 8 inches on the ceiling, 4 inches on the walls. Two years ago I installed a 36k MrCool. On 100 degree days you can hang meat if you want. It took two days when first fired up to pull all the humidity out, after that it just idles most of the time summer and winter. It is hung at 9 feet off the floor. In summer it stratifies a bit and the loft is warm (not hot). In winter I will run a box fan to bring the heat down if I'm going to be working all day. Don't really have to to be comfortable, but it does help a bit. A single unit mounted on the center of one 40 foot wall is plenty and circulates the air just fine. Once the humidity is down you don't need a lot of circulation. That's my story. I'm happy with my insulation and my MrCool. It saw -8 degrees for 4 straight days last winter and kept it around 50 degrees.

 

[Boosted73Z]

Sounds great, it doesn’t get nearly that cold here in south Louisiana, but the humidity can be horrible, sounds like the 36k Mr Cool should work for me, I have 2” closed cell foam on the roof and 4’ of the upper walls and 3” of open cell foam from 10’ down on the walls, one 18x10 insulated door, two walk in doors, one 8x7 insulated door, no windows.

 

[My Old Tools]

Sounds great, it doesn’t get nearly that cold here in south Louisiana, but the humidity can be horrible, sounds like the 36k Mr Cool should work for me, I have 2” closed cell foam on the roof and 4’ of the upper walls and 3” of open cell foam from 10’ down on the walls, one 18x10 insulated door, two walk in doors, one 8x7 insulated door, no windows.

It is very cheap to run. Most of the winter I keep it on FP, freeze protect which is 47 degrees. I turn it up to 68 or so when I'm working. Summers it sits about 78. I seldom. Need it cooler without the humidity, but it will definitely pull it on down.

 

[Black Oak]

I'd consider more insulation if it's not too late . Add some batts in some fashion . A metal building in Texas is going to be a challenge to keep cool .