Installing AC window unit which meets HOA rules

[chet jamio]

I finally decided I needed AC in the garage during the Florida summers. Being in a deed restricted community, my obvious option was to install a mini split system, but I figured I could do it cheaper. My first thought was to install a used 1.5 ton split system without ductwork and just put a filter, evaporator, and blower in the corner of the garage. This was going to be about $900. My second thought was to modify an automotive system for garage use ($600). The large ones are ~25,000 BTU and I have all the tools to evacuate, charge, and maintain the system. What I finally decided on was a window unit with some ductwork.

Here's a picture of the final install. The back portion of the AC which usually hangs outside is mounted in a box. The box has is sectioned to have intake and exhaust chambers which are ducted through the ceiling and out the soffit.

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The following 3 pictures show the AC shell installed in the box. The sides aren't yet installed. The box is centered on a truss. The intake and exhaust ductwork is split left/right at this truss.

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This last picture shows the holes in the ceiling

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[chet jamio]

Here is the ceiling holes as viewed from the attic.

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I needed to ensure the intake and exhaust air pushed through the soffits and didn't circulate within each other, so I added a piece of plywood to seal this area. It's hard to hammer straight when every backswing caused knuckle bleeding on the shingle nails.

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The last 3 pictures show the plywood ductwork I created to cirulate the air over the condenser.

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Overall the system works great. It's a 18,500 BTU unit. I added R-30 in the ceiling and R-10 foam boards to the garage door. It takes 15 minutes to drop the temp from 84 to 77. However, with 2 guys working, a 2hp dust collector, and a 3hp table saw, the AC can't lower the temp any more. It can keep the temp constant, but it won't cool. I'm fine with that. All I have to do is wait 15 minutes before starting.

[Bruce Wrenn]

I have seen similar installations, using the existing window. Build a sleave and bring unit inside. Nothing sticks outside of the house. You may have to add a fan to exhaust side of your install. This would overcome the resistance from the duct work. Remember that exhaust air also carries out condensed water. Nice job!

[Jim Becker]

Don't forget you need to deal with the condensate...I know my window unit drips a LOT and it's only a small one...

Nice installation!

[chet jamio]

Bruce - I agree that using a sleeve in an existing window is an easier method, but I don't have a window. All of my exterior walls are concrete block and I didn't want to fuss with cutting a hole. Also, having an externally viewable window unit violates the HOA rules. I was worried they would even have a problem even if it was recessed.

Jim - You can see my temporary bucket in the first picture. I cut a hole in the bottom of the box directly under the condensate drain of the AC case. This weekend, I will run a hose from the drain to the garage door and let the water run onto the driveway. I'll also be installing a dedicated 220 outlet instead of stealing power from my bandsaw.

I was worried about the additional flow resistance of the ductwork. I haven't done this yet, but I plan to determine the effect of this resistance by measuring the temp of the cold outlet air. My baseline measurment will be made with the unit out of the cabinet and sitting on my bench inside the garage. I'll measure the ambient air temp, and then start the AC and let it run for 10 minutes. At that time, I'll measure the temp of the cold outlet air. I'll then install the unit back into the cabinet and repeat the process the next day. I'll ensure that the outside air is withing a few degrees of the shop ambient air from the first test. If the temp of the cold outlet air is significantly different, I'll start to address the duct resistance. My first thought is that the vent holes in the soffit aren't sufficient, so I'll add some louvered vents there.

[Randy Denby]

Chet, there should be approximately a 30 degree temperature rise across the condensor coil. This will take into account that most window units use a "sling-a-ring" type of condensor fan blade,where the blade will pick up condensate water and sling it thru the coil to help lower head pressure.So, when taking your measurements, make sure the unit has been running long enough to have some condensation in the bottom of the pan. Also take reading on medium speed, if there is no medium then high speed.
Also, there should be a 18-20 degree temp drop across the evaporator......

[David Hostetler]

Chet,

Thanks for linking me! Your idea is top notch for sure! A couple of questions though...

Measurements? LxWxH would help.
Are your walls insulated?

My walls are a wreck due to a prior roof leak (before I owned the house). One of my big projects is refinishing the garage entirely, which will give me a good way to do insulation in the walls / ceiling.

Mine is oddly sized. I have measured with some friends their 2 car garages, mostly because I was curious and asked. And a "Normal" size seems to be...

22' W x 24' D x 10' H. (5280 cu/ft).

Mine is 18' W x 20' D x 8' H with a small bump out of 5.5' W x 2.5' D x 7.5' H (2983.125 cu/ft).

Uninsulated, and leaky as sin around the doors my little 10K BTU Goldstar does what your much larger unit seems to do. If your garage is around the cu/ft of the others I have seen, I can understand the difference. WAY more air to pull heat / moisture from...

I had never considered your approach, but it makes such amazing sense it is scary...

Maybe by the end of this summer my HOA will stop sending me hate mail... Thanks!

[alex grams]

A bit of a bump, but does anyone have any input on how this works with building codes in general? I don't really know how it may violate any codes, but then again I don't really know codes well enough to make much of a solid judgement.

Also, in regards to the exhaust/condensate, is there an internal drip pan on the unit that you cut a hole to drain from?