How do I get even temps in my 2 story house?

July 22, 2007 2:52 PM

How can I make air conditioning work better in a 2 story house?

I live in a newish 2story house with a modern air conditioning/heat system. There is an adjustable baffle that controls air flow between floors, and it works well in the winter to direct more heat downstairs but in the summer even when directing all cold air to the upper floor, the upstairs is 5-10 degrees hotter than the first floor.

Ideally, I'd like even temps between floors. I've heard of houses with separate air conditioners for each floor but can those be retro fitted or does it have to go in during construction? Is there any other option to get a cooled down 2nd floor without freezing the first floor?

posted by mathowie to home & garden (13 comments total)

Do you have a powered vent for the attic?
posted by hortense at 2:58 PM on July 22, 2007

We had a attic fan installed and the difference is ridiculous. In a good way. There's virtually no difference between the first and second floors now.I have no idea if you own a home and can install one, but if it's an option you should definitely look into it. Ceiling fans in the bedrooms is a huge help as well, although not nearly as effective as the attic fan.
posted by iconomy at 2:58 PM on July 22, 2007

Thirding an attic fan.
posted by Blazecock Pileon at 2:59 PM on July 22, 2007

I have no idea if you own a home should be 'I have no idea if you own *your* home'.
posted by iconomy at 3:00 PM on July 22, 2007

Third the attic fan. Even one that works solely by convection makes a huge difference. The amount of heat that can build up in an attic without a fan is staggering.

My former roommate bought a house and it turned out the powered fan no longer worked. He replaced it with an unpowered model, and while it's less effective than the powered one would be, it made a huge difference in the temperature of his attic, and therefore the temperature of his whole house (since he only has a one story)

If you prefer, you could get a separate unit upstairs. Since you have an attic, duct work wouldn't be a problem, although you'd have to lose a small closet's worth of space for the inside unit.
posted by wierdo at 3:06 PM on July 22, 2007

Try closing all the vents on the first floor, it works in the house I am currently in, but I don't know if the baffle you're talking about does the same thing.
posted by 517 at 3:08 PM on July 22, 2007

This site claims that attic fans aren't great in humid areas. How does this stack up with everyone's personal experience?
posted by maudlin at 3:12 PM on July 22, 2007

You can also get small fans that fit just inside the vents to help pull more air through them. Also, if you haven't already done so, try closing off the upstairs vents in any unused rooms, and any vents in hallways. Closing the hallway vent made a noticeable difference in my upstairs home office. It's still warmer up here than downstairs, but it's better than it was.
posted by COD at 3:19 PM on July 22, 2007

Generally without zone controls (rare on forced air domestic systems) your second floor is going to be warmer because of the stack effect.

An attic fan makes the most difference if the attic isn't otherwise vented properly. Go into your attic around 2pm when the sun has been shining on your roof all day and take an air temperature. If there is a 25+F difference between outside and inside an attic fan or better vents can help.

I'm not sure what the solar insolation is like in Portland, though I have the impression it rains more than it is sunny. However if you do get a lot of sun on your roof a radiant barrier can make a _huge_ passive difference in attic insulation temps.

Reducing the attic temps reduces the amount of radiant heat gain from your ceiling.

Closing a few 1st floor vents can help to mix the conditioned air minimizing gradients. However don't go overboard or you'll reduce the overall efficiency of your C/A. Ideally you'd want all your registers open.

You might also be getting more direct solar gain on the upper floor if you have more south windows on the second floor or if the second floor isn't as well shaded as the first floor (a common occurance in new subdivisions with new landscaping). Curtains, the closer to black out the better, will reduce the direct gain.

Also make sure you've changed your filter in the last three months.
posted by Mitheral at 3:49 PM on July 22, 2007

This site claims that attic fans aren't great in humid areas. How does this stack up with everyone's personal experience?

That page is talking about whole house fans, which are indeed best in dryer areas. What is being suggested here is an attic fan -- a fan that keeps the attic temperature closer to the outside temperature, rather than the oven-like temperature that a poorly-ventilated attic creates. They can be electric, unpowered, or solar-powered -- any big box building supply store will have a couple to choose from.

I would suggest assessing the insulation above your ceiling -- if there is too little insulation, you will have a lot of heat gain in the summer (and be losing heat in the winter). If your house is new, you probably meet the current building code in your area, but that does not mean that it could not be better insulated. Your wall insulation may also be inadequate, and things like window shades and shade trees can make a big difference.
posted by Forktine at 3:55 PM on July 22, 2007

I had zone dampers installed earlier this year. My system now works as though I have 2 AC units but I only have one. You can probably get your system retrofitted for less than a grand, depending on how much ductwork they have to do. I couldn't be happier with my system now.
posted by Uncle Jimmy at 4:13 PM on July 22, 2007

For what it's worth, we just got the same attic fan advice for a 1-story house. Our inspectors were a little surprised that we only had soffit vents and no attic fans (whirlygigs are what are common here, actually on the roof, and they recommended 1 per 500sf of attic), given the age of the house and most of the neighboring roofs having them.

They also said that venting the attic would improve the life of our roof.
posted by Lyn Never at 6:22 AM on July 23, 2007

might be too late to comment on this. but i'm curious if the atticfan idea is any good if you are actually living in the attic... then you are blowing your cooled AC air outside
posted by kfs27 at 7:04 AM on November 12, 2007