adding air conditioning to a condo that has forced air heating

January 11, 2010 10:10 AM

What are the options for adding air conditioning to a condo that has forced air heating, but no AC?

I have a 1,000 square foot condo. There are 8 units in the building. 4 down and 4 up. I'm in one of the upper units. I have a gas furnace that is built into a closet that's accessed from my outside balcony.

I don't want to deal with a window unit. I've seen some of the slimline units, but I suspect the HOA would have some issues with mounting the external portions of those. The ideal situation would be to be able to use the ducting that's already in place for the heat, but I'm not sure if a compressor can be added to the closet where the heater sits.

Has anybody done anything like this in the past or have an idea of costs/options? Also, if you know a good HVAC person in Los Angeles, please let me know.

posted by willnot to home & garden (4 answers total)

The ideal situation would be to be able to use the ducting that's already in place for the heat, but I'm not sure if a compressor can be added to the closet where the heater sits.

The ducting for the heat could perhaps be used to pump the cold air around the house, but where are you going to dump the heat from the A/C? A window unit puts the radiator on the outside of the window, and a regular A/C is entirely outside. Do you have a duct that leads to the outside? Can one be put into the balcony/closet door without offending the HOA?
posted by jedicus at 10:52 AM on January 11, 2010

The condenser/compressor (in central air, the big noisy fan part) has to sit outside in the open. Preferably in the shade if you can arrange it, but in the sun won't hurt efficiency too bad.

To answer why you have to know a little something about thermodynamics and how air conditioners work. The outdoors is a "reservoir" in the system: something where no matter how much heat you add or subtract the temperature still stays the same. What the air conditioner does is remove 10/20/30 degrees of heat from your house and puts it outside. And because the outside is such a large reservoir it can accept all that heat without much problem.

So what happens when you put an air conditioner condenser/compressor in a garage, in an attic, or in a closet? Those spaces are small compared to the area you're trying to cool and will noticeably get hotter when you add heat to them. They won't be good reservoirs at all and your air conditioner will have to work much, much harder to remove those 10/20/30 degrees of heat. Overall: much higher energy bills, shorter lifetime on the parts in the system, and decreased ability to cool your house.
posted by sbutler at 11:33 AM on January 11, 2010

As others have pointed out, you know the external portion of the slimline unit? You will need that, no matter if you have a slimline inside or a refrigerant coil put in your central heating system (that simply uses the fan portion of your central heating system, doesn't turn on the furnace, and blows the air through a heat exchanger which is chilled using a compressor and a condenser (the part that sits outside).

What I have seen done is put the condenser (the hot part that sits outside) in a well ventilated place (a room sealed from the rest of the house with a large window which is left open) where the air is sucked through the condenser unit and then exhausted directly outside through a grill in the wall. You can't see the unit from the outside, but the heat is still getting dumped outside without any hot air getting sucked back in to the unit.

Others in your building must have A/C? Where are their units?
posted by defcom1 at 4:11 PM on January 11, 2010

This is Southern California reasonably close to the beach, so I'm not sure that others do have AC. There are only about 10 or 20 days out of the year that you'd really want/need it. I knew that I'd need to vent the heat outside of whatever room(s) i was trying to cool I just wasn't sure about whether that could be in the furnace closet. It is largely removed from the rest of the unit (shares 2 common walls, which I'd think are insulated, and the external facing walls of the closet are not insulated. I was more concerned about condensation/space in the closet, but it sounds like even though the closet is external to the home, it still may need better venting.
posted by willnot at 4:50 PM on January 11, 2010