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Attic A/C?

Hi. I have a 1940's cape cod with a finished attic. Evidently the attic was finished when it was built. I'm going to re-insulate it shortly, since I notice the attic is still hot even though the house is retro-fitted with an air conditioner running through the floor vents.

I was thinking it might make sense to run an additional flexible duct through the 1st floor closet into the knee wall area of the attic, and put the vent near the top of the ceiling. So that the cool air falls.

Then after reading a few threads, I started to think it might make sense to put a 2nd small AC unit in the knee walls of the attic, and not bother with the central AC.. I think the advantage there would be that it would be a "zoned" system.

Any thoughts on my situation, or possible costs?

Thanks for the insight.

Re: Attic A/C?

ASC2078 Idea is the best solution. Most atttic spaces never cool down enough because the thermostat is usually located on the lower floor. Also with out a return in that attic space it would probably never cool down.Besides the heat load from the roof would never keep up and cool the space. I travel for my job alot and stay in hotels (typically Hilton gardens hampton Inns and holiday Inn express). The newer ones have used this sytems in there office and front desk areas. The outside units are right out front. They are quiet and very small. Go check one out and maybe the manager will let you see the inside part.

Re: Attic A/C?

Thanks guys for the info!

I have 2 similar units in an art studio I have in the city. They work great. for a 2,000 square foot room.. A concrete block that bakes in the summer with out them.. Though the electric bill is a bit expensive...

Do you really think a heat pump over insulation and a flexible duct to bring more cool air from a higher vantage point would work better? Adding a return wouldn't be a hassle If we're all readying adding new ductwork...

Insulation will be around a grand or so, but there is that great new energy efficient tax deduction that will be available, so that brings the price down a bit, then adding a duct shouldn't be that difficult, where as, these ac units will require a bit of electrical work, plus, where do you hide the condenser? I imagine with the 30ft kit, I could tuck in on the ground floor by the existing condenser..

Re: Attic A/C?

I am not a heating contactor just a electrician. I would say the heat duct and return would never work to keep it cool enough even with insulation...

Re: Attic A/C?

Yeah, I'm not a contractor either, so I can't say, but my assumption would be the best long term investment would be to start with the insulation and see how it goes. I'll have some quotes shortly to post here for cost on all of the discussed ideas. I'll check them all out

Seeing as there's a $300 credit for insulation:
That's a pretty reasonable incentive to give it a try..

My assumption is that another duct with a booster fan might help, but that would depend on the efficiency of the cooling unit.

I'm sure an additional heat pump would put out more cool air than the duct, but what's the long term investment? Cost per month?

I could also add a solar powered vent fan on either side of the knee walls. It surprises me that there are no vents there at all..

Re: Attic A/C?

You could have additions to your existing central A/C by adding zone dampeners and a second thermostat for the upstairs.

That way the main level dampener will close when it's thermostat setpoint is reached and the second level can continue without freezing out the lower level.

Just a thought.:)

Re: Attic A/C?


All the above ideas are good, but I suggest you first get some insulation in the rafters, along with the rest of the attic walls---especially the rafters.

Attic apts are notoriously difficult to cool---you have the sun beating down right on the roof a few inches away from the ceiling.

It's probably too late for sprayed styrofoam in the rafters, which would be best, but you can still blow in as much cellulose as possible---if they can get some styrofoam in there, let them do that instead.

Once the insulation is in you'll have to do a Manual J (heat gain calculation) to see how much AC you need.


Re: Attic A/C?

Yeah, that was my general thought, but everyone I talk to is agreeing with the folks above, that since there's only a short distance between the roof and the plaster ceiling, that the cellulose insulation is about as good enough. I'm not sure I agree, but none the less, I'm thinking of first trying the addition of a duct with a booster fan. The AC unit is new, so it does push some cold air.. I might also at the same time add a new return, I think the returns in the house are limiting the system a bit.

Running a new duct through the closet seems to be the cheapest first step. I can also always blow some insulation under the attic floor, and insulate the knee walls which have none...

I guess the real key is to get a good HVAC guy in like you recommend..

Thanks everyone!

Re: Attic A/C?

I would strongly suggest having an HVAC specialist come out and perform a survey of your current HVAC system and then determine what is best. You can certainly raise the ideas seen here to them at that time, and then they can see if they are applicable in your specific situation.

Zoning is not a new concept, but is gaining more acceptance now more than ever before. Depending on how large the space is you are wanting to heat and cool, would come into play when deciding what type of system to use.

I agree that the ductless mini-splits have certain applications that meet the need; however, keep in mind that because there is no ductwork you are discharging the air from a single point. If there are two "ends" to your second floor as most cape cods I have seen, then introducing air into one end, may not satisfy the entire second floor space.

You really need someone to determine what size is needed, how the best way is to route ductwork behind the kneewall (if in fact ductwork is used) and so forth.

You mentioned running duct up from the first floor system to the kneewall space. Keep in mind, that there may be ways to incorporate zoning into your present system without the need to change out the equipment itself.

Lots of ideas. That is why a professional needs to look at it.

All the best, Irishmist

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