I Just Wanna Be Cool
June 8, 2011 3:18 PM   Subscribe

Upstairs, Downstairs, A/C issues: how can I help the new A/C in my old house keep me cool?

The setting: a 2 story house, about 100 years old, 1800 sq. ft., in rural NY where summers are quite hot and very humid.

The protagonist: a fussy lady who's already having hot flashes, dammit, and who gets very cranky if she's overheated.

The issue: whether and how to use window fans to exhaust hot air upstairs, with A/C running.

The details: My old house was retrofitted a few years ago with central air conditioning. We used the existing ductwork of the forced air heating system (single zone), reconfigured a bit for better efficiency by my superlative contractor. It wasn't possible to create separate air outlets for the A/C, so the cool air comes out at floor level. There's enough overall air circulation in the house (I keep the A/C fan on continuously during hot spells) that this isn't a problem at all on the first floor, which is perfectly comfy. The upper floor, though, ends up being ~4 degrees warmer than the first floor, which is too much difference for real comfort. The cool air comes out of the vents upstairs, slinks along the floor and heads right downstairs. Keeping the doors to upstairs rooms closed helps some, but that feels stuffy, and the cats do not approve.

The ceiling above the second floor is very well insulated, and the attic is ventilated. There are no ceiling fans upstairs, and the rooms up there are really too small to accommodate them gracefully (and I need a do-it-myself solution, and my self is not up to that). I've done what I can with shades and drapes to keep the sun out.

So here's the solution I'm working on, but I'm not sure it's a good idea. I put a window fan like this (2, 7" fans) at the top of one of the double-hung windows upstairs, blowing out on low speed. I think it moves ~500 cu.ft./min. (that's a guess). That does a very nice job of blowing the hot ceiling air out, and invites the nice cool air to get up off the floor. That room feels much more comfortable with the fan on, and I thought Hurray! and bought a similar fan to put in the other upstairs room that needs help. But then I thought, with all that air going out, there's got to be more air coming in. HOT, HUMID, SWAMPY air from outside. It could come in by way of ground level vents that let air circulate through a crawl space that is connected to my basement by a door that I can have either open or closed. Or, if that door is closed, the air would have no way to come in except random infiltration.

Other options: Before I tried the window fan, I tried using a table fan in each upstairs room to just stir the air around, but that is surprisingly ineffective, and feels too windy. The window fan creates a much more comfortable situation. I could get a small room-size A/C, window or portable, for the remaining hot room, but I'm not sure the wiring in that room is up to that, and it also seems like it would be way more inefficient than the fan(s).

So my questions:

Assuming that having the window fans in 2 upstairs rooms makes the house more comfortable, is that a bad idea? Would constantly pulling in that additional amount of hot, WET air from outside make the A/C work lots harder, and cost way more when it's time to pay the bill? Or would the difference be no big deal? The A/C equipment was carefully sized for the house, and it has no trouble keeping the temperature and humidity in the house just right, except for the stratification upstairs. If I do use the fans, would it be best to run them 24/7, so the heat doesn't build up, or just at night (which is when I'd usually be upstairs)? If I use the fans, would it be better to facilitate air intake through the basement by opening the door that connects to the crawl space, or keep that closed and rely on infiltration? Is it hot in here, or it just me?
posted by Corvid to Home & Garden (11 answers total) 5 users marked this as a favorite
 
Is there a door at the top of the stairs that can be closed off. This would keep the cold air upstairs. Of course you will need an air return upstairs also. As for the cats install a pet door.
posted by tman99 at 3:37 PM on June 8, 2011


Same issue here, retrofitted 100-year-old house with a south-facing upstairs bedroom. We got a $100 window-unit air conditioner, installed every Spring, taken out every Fall.
posted by MrMoonPie at 4:21 PM on June 8, 2011


Have you tried air deflectors?
posted by thomas j wise at 4:24 PM on June 8, 2011


tman99: nope, no door at the top of the stairs, and it's not configured in a way that would make that a possibility. No air return upstairs, either (except the staircase)--that may be a future construction project. I'll bet it would help.

thomas: air deflectors help in some spots, but still keep the air near the floor.

Still looking for opinions re the exhaust fans--OK, or bad idea? Thanks -
posted by Corvid at 5:12 PM on June 8, 2011


Same issue as you and MrMoonPie, with 100-yr old, two-story house, with same stairway door issues.
When we updated the forced air furnace/AC the contractor wanted some way to get the AC up to the attic level to drop into the rooms from above. I found an 18" square alongside the ancient brick chimney which runs from basement to roof. The "empty" space was in the end of small closet spaces on the first & second floors. It now houses a duct to the attic which spreads out in four insulated tubes to drop into the upstairs rooms. It seems to do a much better job of getting the AC to the second floor rooms.

I recognize this may not be possible in your architecture.

I think the exhaust fans in the upstairs windows are a poor solution. For AC you want as much of the return air to the furnace to come from the uppermost point in the living space. If you are blowing out partially conditioned air from the upstairs, you are pulling it in from the humid outside and/or the crawl space.

MrMoonPie's solution with a window unit seems very workable. You are keeping the conditioned air in the room and just supplementing it when you need it.

Although you may not have room for ceiling fans in the upstairs, perhaps a wall-mount fan would work. Ones with a built-in oscillating motion would bring down the warmer air from above and distribute it around the room. When they are run on low speed, they don't use much electricity and can help you, or more importantly, your lady, "feel" cool just by stirring the air.

(the link is not a recommendation for a particular model, just an example like ones I've used with success.)
posted by tronec at 5:48 PM on June 8, 2011


Air return upstairs would definitely help. We have a similar situation with the Cape Cod we're living in (with the master bedroom upstairs) -- all but one of the upstairs vents are at floor level (there's one at waist height on a half-wall surrounding the stairwell). We've been told by the HVAC guy that the only reason this system works is because there is a generous air return upstairs, on the (slanted) ceiling. It pulls the hot air from the top of the room out, creating opportunities for the cool air to actually get moving in the space.

Despite that, without intervention, it's regularly 5-7 degrees hotter upstairs than downstairs during the day during warm weather. We do a few things to combat this.
  1. We keep the HVAC set a couple of degrees cooler than we otherwise would to keep it pumping more cold air upstairs. This may not work for you if you run the HVAC fan all day, but you might give it a try.
  2. We use small table-top fans (like this one) in front of the upstairs vents, pointed slightly upwards, to get the cold air circulating up towards the ceiling. We put them on the slowest speed so it's not too windy, but there's still a noticeable breeze. We have gotten used to this. Bonus: the fans serve as a very nice source of white noise at night.
  3. We close off several of the vents downstairs to push more air through to the upstairs. (HVAC guy was dubious that this does anything, but it makes us feel better and doesn't seem to hurt the unit. Also, we absolutely don't need to be air conditioning our [freezing] basement, so closing off that vent, at least, was a must.).
My instinct is that the exhaust fans aren't a great idea for the reason you mentioned -- they're getting rid of hot air, but only creating an opportunity for that hot air to come in from elsewhere. This is going to affect how efficiently your HVAC unit runs.

Finally, I will admit that we've been tempted by MrMoonPie's solution, and it seems to be pretty common in the Cape Cod homes around here. With a window unit upstairs, you can also stop running the fan all day, which will save you some cash and improve the efficiency of your unit.
posted by devinemissk at 5:51 PM on June 8, 2011


How about a duct booster fan? I had the exact situation and this fixed it. It's wired right into the fan in your furnace so it comes on when the high speed fan setting fires up with the AC coming on.


posted by PSB at 6:10 PM on June 8, 2011


Here's a link to a duct booster fan.
posted by PSB at 6:14 PM on June 8, 2011


We're in a similar situation and opted for a window air. It works well, provides white noise at night, and lets us keep our central air off at night.
posted by jmsta at 3:08 AM on June 9, 2011


We have a similar situation and 1) close all the 1st floor vents (they still let some air through & it's still quite cold on the 1st floor), and 2) keep a small Vornado fan running at night to cool things off & keep the air moving on the 2nd floor while we sleep. It works.
posted by ImproviseOrDie at 6:09 AM on June 9, 2011


If the difference is only 4 degrees I would experiment by turning the thermostat down 2 degrees and close the vents downstairs. Maybe that little bit is enough to make a difference.
posted by CathyG at 9:52 AM on June 9, 2011


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