In Two Months, I Will be Frying
February 19th, 2009A/C Help
Help me out again. I asked about this a long time ago, but now I’m serious. I want to put an air conditioner in a cinderblock garage wall. The garage has become an even better refuge than Frank Costanza’s “The Place to Be,” but it won’t be much of a refuge when it’s 90 degrees in there with 80% humidity.
I have determined that a 115-V unit 18″ high by 24″ wide, pumping out 15,000 BTUs, should do the trick. The space is 565 square feet. It’s not insulated, and I suppose I could go above 15,000 BTUs to be sure, but I hate to cut a bigger hole, and I’d really like to stay at 115 volts so I can avoid running a third circuit.
I need help with the hole. I believe it will have to be 26″ by 20″, which is not much. I can put a special blade in my ancient circular saw and make the hole. But what do I do to finish it? The unit has to sit on something, and I would want something across the top of the hole to support the cinderblocks above it.
I assume there must be a product made for this. I suppose I could fake it with pressure-treated wood, but that would make me nervous.
February 19th, 2009 at 4:42 PM
Have you considered a free-standing unit? Some of them can put out as much as 15,0000 BTUs or more.
February 19th, 2009 at 4:44 PM
I want to do it right, with a wall unit.
February 19th, 2009 at 4:44 PM
You might enjoy cutting your hole in the block wall using your air compressor and an air chisel. Yes, the chisel will dull a little but you can easily resharpen. You might even use the air chisel to cut back at the top corners so you can slide an iron or steel lentil in place to support the blocks above. With your wood working tools you can make a window frame to fit your air conditioner. The insulating foam in a can stuff can lock your window frame in place. Looks to me like you have everything you need to do this simply and easily except, maybe, the air chisel. $20 or less should buy a cheap one from Harbor Freight that will do nicely.
February 19th, 2009 at 4:45 PM
Actually, I have an air chisel. I don’t need to know how to cut the hole. I need to know how to finish it and make sure the blocks above are supported.
February 19th, 2009 at 5:18 PM
Check out the small split systems, then you would only need a small hole for the copper lines and power. Might be a little more money up front but I think they run cheaper than window or wall units.
February 19th, 2009 at 5:19 PM
About $1400, compared to maybe $400 total for a regular unit.
February 19th, 2009 at 5:21 PM
Consdiering your hole will be 24″ wide (and hence will span at least three cinder-blocks), you’ll probably want a Steel Lintle Support for the top. I don’t know what code is in Florida…the Cinder-block buildings around here seem to use 1/2″ thick steel plate.
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For the bottom and sides, you’ll probably want something that is moisture/rot resistant…I might look at some of the solid plastic decking or 2×6’s they make for outdoor decks. You can cut and drill it pretty much like wood. After you frame it, use the expando-foam for insulation around the frame.
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Someone might make a complete frame for this (like they do for pre-hung doors); if so, I’ve never seen it,,,maybe ask at Home Despot?
February 19th, 2009 at 5:25 PM
Er…make that “at least two cinder-blocks”.
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I was using my fingers for typing so I couldn’t count 🙂
February 19th, 2009 at 5:46 PM
What’s wrong with pressure treated lumber frame? That small a hole really can’t do much to weaken the wall IMO. Alternatively, Have the top start just below a mortar line, remove a few inches of mortar on either side of the vertical cuts and slide in a correspondingly thick piece of steel plate to span the opening and then frame the sides and bottom with wood. Surely a steel plate the thickness of the mortar will be stronger than what you are removing.
February 19th, 2009 at 6:16 PM
A masonery drill, a 2 lb sledge hammer and a chisel is all you need to take out 1.5 blocks wide by 2 high. The support for the blocks has to be a steel section that goes about 3″ into either side of the remaining blocks at the top, mortar it in place after inserting. Use a board at the bottom and a 2×4 a bit longer than the opening to wedge the steel plate at the center then mortar in the slots on the side and fill in the rough spots from the chiseling as well. Being FL I would use the plastic composite boards or treated lumber to box in the sides and base. I did mine by putting a nice wide treated board across the base, full width, then measuring and wedging the two verticals, one per side to add support to the steel lintel. Then trimmed it all with molding, looks like a glassess window frame from both sides of the wall when done. Insert the A/C unit and have at it. With all the rain you get, might also want to get some sheet aluminum and make a roof over the outside exposed parts with a nice angle to move the water away from the opening.
February 19th, 2009 at 6:26 PM
Thanks. How did you connect the wood to the blocks? How thick does the steel have to be?
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I’ve seen premade steel lintels on the web. They look pretty thin.
February 19th, 2009 at 6:53 PM
Steel would be whatever the thickness of the mortar is, so that it would just slide into the slots. Or two pieces half the thickness, etc. I would think there are plenty of construction adhesives that would adhere wood to cinder block but really if the wood parts were cut to close tolerances then they would wedge together pretty tightly. Hell, put the wood in the oven warm/ low for a while then cut them to size and install and they would quickly swell back up to fit tight as a drum. Go for it, dovetail the corners!! Do you have a dovetailing jig?? Joke. I’d fit the AC unit into the frame before installing the frame pieces into the wall. You’ve got the tools to manipulate the sizes and thicknesses however you need. Plus, this way you get to go steel shopping.
February 19th, 2009 at 6:53 PM
If you cut the blocks in the middle- that is, if you cut a 24″ wide opening starting at a vertical seam and going 12″ either side, you’ll still be safe. So long as you have no more than three or four courses of block above the window unit. If you’re still concerned, cut at the horizontal mortar joint and again 2″ below it, and slide in a 2×8 to act as the lintel. Let it extend 6″ either side of your opening. Then cut the hole and put in the rest of the framework. The wood lintel is plenty, esp. if you use pressure treated. Use mortar mix to secure everything once squared up.
A lot of hammering is a not good idea if you don’t use the lintel.
The easiest way to cut the opening is to use a hammer drill to drill holes all the way through at the corners. Then saw cut to connect the dots inside and outside. Cut the bottom first, and you’ll know when it’s free by the block falling down.
February 19th, 2009 at 6:56 PM
Vertical seam above the cut or below?
February 19th, 2009 at 6:57 PM
“How did you connect the wood to the blocks? How thick does the steel have to be?”
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Not sure if this was to me or not…
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I would think that 1/4″ to 1/2″ would surfice. The lintle thickness they use in Cinderblocks here vary according to span. The 1/4″ is used in single window sized openings (33″ or so).
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Usually a frame made of 2×4’s is “cemented in”, and the sill and side boards are nailed/screwed to that. This means that the opening has to be at least 4″ wider to accomodate the 2×4’s, side boards and sill (3″ for the 2×4’s and 1″ for the sill/side boards). I think you can still use the “plastic wood” for the frame.
February 19th, 2009 at 7:10 PM
Not sure what you mean. I see it as the verticals starting just below the mortar line and going down however far they need to so as to allow room for the AC unit plus the bottom & top framing thickness. Or go with a mortar line as the top and at the bottom and fill the extra space with wood, that way the only actual cutting would be the verticals. I would think that whatever blade you use for cutting the blocks would go through the mortar like butter.
February 19th, 2009 at 7:40 PM
3/8 ” will be enough thickness for the steel lintel. If you are careful and the top of the hole is the base of a row of block then you should be able to chisel out the mortar on both sides at the top and slide the lintel into that space. You only need about a half inch on each side to start with. Cut the whole a little wide then use a couple of pieces of scrap lumber held in place by a couple of pieces of 3/8 rebar bent like a U but which forms sort of a tong type grip at each end. These are used to pinch the two boards against the block wall leaving about two to three inches sticking out into the opening. (the edge of the boards will be the finished edge of the finished opening) Then mix some concrete fairly dry and pack it into the space between the two boards (again, one of which is pinched to the outside of the bouse and one to the inside forming a channel to take the concrete.) Be sure and wet the cut block surface well where it has to take the concrete and it will take about two applications and then the last one smooth down nicely with a strike off board. Do that on both sides then the same at the bottom of the window. What you have then is two concrete bond beams supporting a 3/8 inch thick steel lintel. Mortar mix should be packed in well between the lintel and the block above.
All concrete, bug and waterproof at less cost then anything else. Use a couple of pieces of rebar in your bond beams and it will be good for a few hundred years.
February 19th, 2009 at 7:56 PM
In a bearing wall, you are going to want some sort of lintel in there, even if it is a small hole. With a 24″ wide hole, a wood lintel like og describes will be sufficient. If you go with steel, 1/4″ is plenty.
The correct tool for cutting the hole is a gas-powered demo saw. It can be done with a circular saw, but it’s going to take a while and may ruin your saw. If it’s an old crappy saw and you don’t want to drop the bux on a rental demo saw, cut away!
To secure the pressure treated AC frame to the block you will want to use Tapcon (http://www.concretescrews.com/tapcon-questions.htm) screws. Be careful not to over-drive them.
February 19th, 2009 at 10:42 PM
Keep in mind that I’m pretty much incompetent with anything resembling a tool, but why don’t you make 2 window frames from angle iron & tie them together with a plate at the top? That should eliminate your concerns about support and rot.
February 20th, 2009 at 6:58 AM
Split Units – they are the way to go. The efficiency is greater, burglars can’t go through the hole, you don’t have to worry about screwing up the structural integrity of the wall, and hurricanes don’t knock ’em out
My guess is the 15 k BTU will be too small – it wouldn’t do squat here on Guam other than reduce the humidity some and our ambient temperature is likely less that yours in the summer time. Maybe you have a termite food wood roof with insulation that doesn’t pick up too much heat.
Good luck.
February 20th, 2009 at 8:54 AM
vertical seam centered above the cut.
February 20th, 2009 at 9:15 AM
See above price figure for split unit.
February 20th, 2009 at 9:41 AM
split units also require a saggy pantsed technician with special tools to install. Hm. Special tools.
Nah.
February 20th, 2009 at 1:40 PM
You might consider a 220V AC unit. You’ll get a better motor, and they’re going to hold up better in the long run than a 110V that has to struggle against that Florida heat & humidity. I had a 220 wall unit that would turn the room it was set up in into a meatlocker when set on the lowest setting, and set at a normal rate would easily cool 500 sf of the house. With a couple of fans to set up an air circuit, it would chill down the living room, dining room and kitchen.
February 20th, 2009 at 1:43 PM
Take out a 220 circuit to put in a 115 circuit, and then take out the 115 to put in 220? I don’t think so.
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The voltage shouldn’t have anything to do with the cooling power, unless there is some deep mystery of evaporators and condensers of which I have not been made aware. Horsepower are horsepower, regardless of the voltage.
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This thing will have to run about 15 hours a week. Chinese will do fine.
February 20th, 2009 at 3:58 PM
The best part ofd a cheap wall unit is when it stops working (which will take 200 years, at that duty cycle) you use the new unit to push the old unit out of the hole in the wall and you’re done.
February 20th, 2009 at 5:52 PM
Steve
I just checked the steel above all the basement lights in my house which are just about the size of what you want for your opening, they are just under 1/4″ thick (about the thickness of a #2 pencil) and are carrying one layer of cinderblocks above the window frame, with the floor & wall framing over that. I suspect you could use a thinner steel plate if you welded a length of angle iron along the center to make it less capable of flexing (tension member). Over engineering is always a better bet. Go with full 1/4″ and you should be fine.
February 20th, 2009 at 6:06 PM
Thanks. I contacted a pro, and he informs me that for this size hole, I don’t need steel. Advantage: Og.
February 20th, 2009 at 6:48 PM
Sure you don’t NEED steel, but if you got a choice 😀
February 20th, 2009 at 9:52 PM
You could also buy a casement AC unit. They’re a tiny it more expensive, but they’re tall and narrow, making it an even smaller hole. Here’s one that’s 14″ wide, 20″ tall, and has a remote control.
http://beta.sears.com/shc/s/p_10153_12605_04275123000P?vName=Appliances&cName=Air+Conditioners%2C+Fans+%26+Heaters&sName=Specialty#desc