Putting AC unit in concrete block wall of shop
Don’t know if this is the correct forum for this, but I figured I’d start here.
We are building a new home with an attached shop on one end of the house, 20×25, and the outside wall is 8” cinderblock, with all cells poured and rebar in place. We don’t want the shop to be part of the main HVAC system because of dust, paint fumes, solvents, etc. But in Georgia, you really need to have AC because of both the summer heat and the humidity.
So, we considered a mini-split but those are outside our budget range for the shop. (Best quote, about $4,500) Next, we talked to a couple of contractors about a PTAC unit (the same sort of unit they put through walls in motels), that provides both heating and cooling… not that we would need the heat very often. That would be about $1,500 installed. Less, money, but you know… save it where you can!
Just this last week I got a flyer in the mail for Sears window units on sale, that do both heating and cooling. As I say, the heating would be minimal. A 12,000 BTU unit would cost me less than half the cost of the PTAC unit, even including renting a bulldog saw to cut through the wall, or paying someone to do it for me.
That being said, is such a thing compliant with the NEC or other IRC rules? If not, can you give me chapter and verse on that? For that matter, if it explicitly IS allowed, it would be great to have chapter and verse on that as well.
And do you think it would be sufficient? I think so, since it is rated to cool/heat about 675 SF, and I have about 500 SF of space.
Thanks!
— Tony
Replies
Dunno about IRC or local codes, but any new AC sold must (for all practical purposes) be UL approved and hence in compliance with NEC so long as it's properly installed. You need to have the proper 240V outlet installed, on its own circuit.
To know if it would be sufficient it would be best to go through a rough heat gain/loss calc.
Thanks, Dan, but that much I knew. I've searched the NEC and the IRC myself for any annotations on the subject of using a window unit for a through-the-wall installation, but have found nothing relevant to whether or not it is allowed. I'm just trying to avoid cutting a big freakin' hole in a concrete-and-rebar wall if it's not going to fly as regards various building codes.
I have found a couple of through-the-wall units I will investigate, so the point may be moot anyway.
Look up the install instructions for that unit on the web, and see what they say.
Tony
Do not size this opening for one specific unit. Cut the opening to fit a well figured size panel, install the AC through that. If this unit craps out, you can more easily adapt the panel.
You'll find the thickness of your block too deep to allow a good install. There's often vent grids on the side that are meant to ventilate the unit. Works fine in a window thickness install. In addition, proper draining of the box might be affected.
I see enough of these installed to believe they are available for an 8" thick wall (louvers far enough back etc). My wife has at least 8 at the golf course she manages. (course bathrooms)
I do agree you are better making the hole a little bigger than the biggest unit you plan on getting and buck it in. Usually you install the can and then put the slide in tray with the refrigeration unit in on the bigger models.