What size window unit?

[benitslu]

Just finished building my pole barn. Trying to figure out what size window unit I need to go with for my 16' x 25' building? I am thinking 10,000 or 12,000 BTU?
It is wrapped in the bubble foil insulation with two windows and a 10' wide roll up door that doesn't get direct sunlight. No ceiling, just exposed truss up top with a ridge vent.
It doesn't need to be frigid when running, but something to make it tolerable in the Louisiana summers.

 

[Bigbandguy]

You are going to lose a LOT of cool in the truss space. I would definitely go with the larger unit if you are not going to install some sort of ceiling. You may end up needing an even larger unit. I would figure out some way to float a ceiling and hold some of the cool in the lower part of the building.

 

[jjrbus]

I would minimum close off the truss area with plastic sheeting or foil faced insulation board taped at seams. Only my opinion, not to be misconstrued as expert advice.

 

[benitslu]

I have thought about but like the added height for when I may be working on something. May give it some time to see.
Yea, I am thinking no less than 12,000 BTU with the open area up top.

 

[benitslu]

If I were to do this, think I would be able to get away with a 10k unit?

 

[TractorJeff]

Food for Thought!
Hot air rises, Cold air sinks.

 

[pattenp]

You may need at minimum 12000 BTU because of your location and building insulation. I'd consider 14,000 BTU.

 

[JRC3]

In Ohio I have a 24x24 8' ceiling with plywood laid on the rafter ties and no insulation above. No windows and a non insulated overhead door. My walls are insulated with Styrofoam, maybe R6 plus drywall. I have a newer 15K window unit mounted through the wall and consider it to be the minimum size for my setup.

 

[Jim greengo]

I'd figure out a way to put a small one on each end,window airconditioners arent really good at moving air across a large area.

 

[Bigbandguy]

A cheap box fan in tandem with the window unit helps a lot. That is my cheap solution for moving the cold around. When I was growing up my dad got a deal on a 24000 btu Gibson window unit. Central AC was way out of his budget but with that Gibson we cooled the whole house. It was in the window of an unused room and we used that room as a cold box and blew the air around the house. Considering Georgia Summers it worked pretty well.

 

[Bruce Amacker]

In Ohio I run a 24,000BTU unit in a similar space, and it's well insulated.

 

[GypsyR]

I've got 900 square feet. Stick built, open trusses. R15 all over everything and dual insulated style Clopay bay doors. I have a 24,000 BTU and in the height of summer here it can't really keep up. Also I have two ceiling fans and a dehumidifier. Were I to do it over again I think I'd try to recycle a heat pump system from a mobile home or something. I may yet if one pops up.

Spring and fall it's quite comfortable. High summer it's cool but if you get to doing something like hammering metal, nope. Have to have a fan. Amps up the power bill pretty good.

In short, my setup is better insulated than you describe and a 24,000 won't really keep up. Maybe duals, if you can swing the electric bill.

 

[JRC3]

I think bigger is always better but not so big it wont dehumidify properly.

 

[Falcon67]

He's in Louisianan. If hes in the southern part, then he'll need a s**t load of AC to even start pulling water out of the air in summer. 12K many not enough especially with an open ceiling. 15K maybe. We're dry here and my old 20x24 with 8' ceiling a full insulation worked well with a 12K unit.

 

[dcg9381]

I think bigger is always better but not so big it wont dehumidify properly.

Less of a problem with modern "inverter" ductless systems that can scale back their cooling capacity.


This is no manual J calculation, but he's got a steel building, 400 sqft, but it's almost 2-story. He's got a 10' garage door with minimal (if any) R value and his main insulation is bubble wrap - little R value. I assume exposed roof deck under composite shingles. This is basically a heat box.

If it's going to be cooled only when used (meaning the HVAC isn't running most of the time) - I think he's looking at 2 window units or a something like a 24k ductless unit (about $1200). He'll need something to knock the heat out and basically fight the lack of insulation.. Open that garage door once and you're starting over.

I agree with others that a big component to shop "comfort" in the south is to come up with a way to move air around...

 

[JRC3]

his main insulation is bubble wrap - little R value.

Sorta missed the "bubble wrap" earlier. If it's that foil colored stuff in a roll they are deceiving with R values. They advertise high R value but that's only when when using it to make double pockets between tall floor joist. When it's one layer it's only good for like R value of 1. I think it's good at reflecting heat when used on roof rafters. https://www.menards.com/main/items/media/REFLE001/Install_Instruct/Rtx__II_BP_ST_DIY.pdf

Less of a problem with modern "inverter" ductless systems that can scale back their cooling capacity.

This is about a window unit.

 

[Falcon67]

Have a friend in south Texas with a new shop, down near Lufkin. His building is metal - and sweating like a pig due to the change from 70F to cold this week. Metal buildings in coastal states sweat buckets on temp changes. Big *** fans help.

 

[nsula_country]

Have a friend in south Texas with a new shop, down near Lufkin. His building is metal - and sweating like a pig due to the change from 70F to cold this week. Metal buildings in coastal states sweat buckets on temp changes. Big *** fans help.

Tell me about it.

NW Louisiana, Was 80* Wednesday, was 32* this morning. Floor was starting to sweat in a few spots this week with doors closed. Bumped ceiling fans to medium and let air handler run on continuous fan. This helped tremendously.

Need to get condenser unit sweated in.

CT

 

[gemniii]

In NE Mississippi I've an "apartment" in the back of one of my shops. It's has one room about 15'x24', insulated ceiling, fiberglass batting in the walls. I run an 8K window unit (I think) and it barely cools the place down to 78 deg F in the heat of the summer.

Above the ceiling there is an empty attic and it's on the backside of building and in complete shade.

If you are trying to save money I think you should get a 10 or 12K unit and get another one as soon as your area warms up, maybe an 8K unit for supplement. But you might need another 12K unit.
If money is no object get a 24K mini-split.

 

[pbon]

Would something like an 18k Friedrich for $600-700 do it? Cools my 750SF insulated garage in NH but LA is much hotter. I think these Friedrichs go up to 24k. Obviously 240V. I put mine through the wall but it is only 17x27 and should fit any window wider than 27.

 

[Tim C]

In the NC Sandhills, where it's plenty humid and high 90s to 100 in the summer I cool my 24x30 pole barn with 12' to the bottom of the open rafters with a 24k window unit and a 2 ton home package unit heat pump.

I also only have the bubble wrap stuff and mine has no shade at all. On the hottest days with both running it cools down to 73 to 75 degrees but it's much nicer than outside. At night or cooler days I can often get by on one. I prefer upper 60s for temps when working.

Before I was given the used heat pump, I used the 24k and a 8k in both windows. That got it into the upper 70s to 80 mid afternoon in July.

I only run mine when I'm out there, too so they have to pull down from 115 or more sometimes but usually do it in an hour.

The 24k window unit also has electric strip heat and it and the heat pump are what I warm the shop with in the winter.

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