My mothers house has an 18,000 BTU wall unit mounted in the living room wall. It works OK, but the hot air is exhausted into an enclosed garage, therefore the when the AC is on the garage doors have to be left open to provide cross-flow ventilation. This has been the situation for 30 years now, the AC can't be left running if you need to leave the house unattended and the garage doors can't be left open all night while my mother sleeps. The garage gets way too hot and we feel that this trapped heat will only make the house hotter.

The garage is a single story 10 by 23 foot with 8 foot ceilings, there is a 3x4 foot opening in the ceiling ( dead center of the garage) which leads to the attic, it is always open, it doesn't have a hatch or door.

My idea is to install a thermostat-controlled attic fan in the east facing slope of the shingled roof.
I am not sure if this will help, I wonder how many CFM's of air the fan should be rated at, where should I put the vents in the garage, and is there a better way to ventilate a garage??????

If any of you live in a Levittown house built in the 50's it is a Jubilee-style house.

 

I'm not clear on this but are you saying the flue gases are being exhausted into the garage? Or the the heated air is?

Where are the flue gases exhausted to?

I hope not into the house.

I definitely can't help you hear, but maybe someone who is a HVAC specialist
could, with maybe some more information.

Good luck

 

The current situation is such that the heat being removed from the living space is being rejected into the garage (A/C is just a heat pump). What is happening is that this accumulated heat in the garage dimishes the performance and efficiency of the window unit. Although it will take some work, I would highly suggest and encourage moving the unit to a position where the heat is rejected to the outdoors rather than try to ventilate the garage. I'd weigh out the work to move it against trying to ventilate the garage.

BTW and FYI, for fire safety that opening in the garage up into the attic should promptly be closed with sheet rock. Install a piece of sheetrock in a manner that it can be removed by lifting s/t you can still access the attic. In the even of a fire, that opening will allow flames to race into the attic (ie, act as a chimney/blowtorch to be more specific) and accelerate the advancement of the fire as well as reduce the detection/escape time for the people inside the home. Someday when the home is sold, plan on that current opening being flagged by an inspector hired by a buyer for the reason noted here.

 

I called it a "wall unit" I mean that it is an air condtioner installed in the wall. My Mother is old and doesn't like change, the AC has always been there, and she even refused my offer to pay for central air to be installed. She has had some bad luck with contractors lately, and this leaves me doing everything at my mothers house.

Bottom line... I have to get the hot air out the garage, so the AC can be run with the garage doors closed.

In this neighborhood and in the type of house we lived in, it was common to install the AC in the wall between the garage and living room and just leave the doors open. I am hoping I can pull the hot air up thru the attic, but I'm not sure if this is a good idea, since I'll have to figure out how much air to move, and how will I get fresh outside air into the closed garage.

 

I had a neighbor that remodeled and added a room on to his house. He enclosed the central AC condenser unit in a closet in the new addition then wondered why his AC didn't work... The AC unit should be in an outside wall.

 

Home Depot sells the attic vent you mentioned

it moves 1500 CFM air so should be adequate to exchange all the air in the garage in under 2 minutes. (garage=1840 cu ft 10x23x8)

But I see no reason to move the air up into the attic. You could mount this in an exterior wall of the garage high up under an eve and still acheve the same result without adding additional heat in the attic that could radiate back into the house.

You could mount louvers in the lower section of garage door to allow fresh air entry.

Question: Where does the condensate for the AC unit go? Is it piped to a floor drain or is it dispersed with a slinger fan into the exhaust air stream?

Dialtone

 

another option: build a plenum wherever the discharge air leaves the condensor and duct that to the exterior, like a dryer vent would work. I'm thinking if it is large enough it shouldn't hurt the efficiency enough to notice (back pressure= reduced flow=less heat exchange, but you know that allready ) and if it does, an in-duct helper fan, tied to the the supply of the condensor fan might even make better cold.

 

The plenum is a good idea! But it would take up too much space.

 

I understand from experience that older folks often don't like change, but explain to Mom that the installation of an A/C unit rejecting heat into the garage was a mistake that never should have been allowed to happen in the first place and should now be corrected. Another option, although it will require some fab work, would be to fabricate a painted steel enclosure for the condensor and the fan, remove the condensor, fan and shroud (if existant) from the wall unit and install it in the new box that will be located outside, then plumb/charge/wire it up. Remember to insulate the suction line as it will sweat and drip. A hassle, yes, but Mom can have the familiar unit in the wall and the problem is solved. Also, if you look around there are wall units available with the condensing unit separated from the evaporator/air handler.

BTW, on the safety hazard I noted in my earlier post, remember that installing an attic fan that turns on with elevated temperature (including heat from a fire) in the situation you have will only aggravate the hazard I noted. A 1500 CFM (25 CFS) fan drawing air through a 3' x 4' hole into an attic, with a fire going, is scary as hell. Use this fact in conversation with Mom to try to convince her to fix things correctly.

 

a 18,000 BTU ac is a 1 1/2 ton unit. Now in terms of air, a ton of ac is rated approximately 400 cfm, so your moms is probally around 600-800 cfm. This rating is on the supply fan, but the exhaust will be very close.

Now, I agree with the attic fan and its fire hazzard. Be very careful adding fans in a garage, because of this hazzard. I wouldn't exhaust into attic, but could exhaust through the attic to the outside or by using the eaves. But not directly into attic.

There are other options other than central air. There are mini-split systems that are wall mounted but use copper lines to an outside condenser. You won't be able to relocate existing condenser or compressor. The PTAC (wall units) are not rated to move the refrigerant that far. Premature(and quick) compressor failure would occcur. Not to mention that you ahve defeated the UL rating of the unit and if your insurance company found out, they could cancel your policy or worse a claim if you had one. If thats not an option, and you're not willing to give up the space for duct, then mount louvered grilles low to the floor and mount the fan up high. That way you pull the heat off the ceiling and bring in fresh air down low where its typically cooler.