A 3-story residence has 2 furnaces w/cac .The stairway is open all the way down to the basement.?

Question

A thermostat is located in the first floor where the furnace is in the basement.It supplies the basement and first flr. A 2nd thermostat is in the 2nd flr.and furnace in the attic that supllies attic and the 2nd flr. During summer when cooling the attic and 2nd flr. does the attic A/C work harder since the cold air goes to the basement and work its way up to the 2nd flr where the thermostat is located?Is the reverse happening on winter? in heating the basement and 1st flr, does the basement furnace work harder since heat rises to the attic down to the 2nd and 1st flr and finally the basement? Whats the least invasive solution?Not using zoned hvac w/c cost alot.

Answer 1

Yes, I think you have the right idea here:  hot air rises and cold air sinks.  I have a 2-story house with one heat/AC unit and it is hard to keep the upstairs cool in the summer.  In winter, I just shut all of the upstairs ducts and it stays pretty comfortable up there.

One thing you can do is to try to circulate a lot of air around the house on all levels.  Your A/C blowers will help, but I've found ceiling fans help a lot, too, especially reversible ones. At bedtime, I reverse the downstairs ceiling fan and it blows cool air directly upstairs into my bedroom.

Answer 2

When you say "attic" do you mean a finished room on the highest level of your house or "attic" as in a real hot place where the insulation and spiders are?

If you mean attic like I think of attic, then you don't need to even try to cool it. I'd put in an attic fan and try to draw some heat out but that's all.

To answer your question... no, your upstairs unit does not work harder.  The a/c unit and furnace only works as hard as it can at all times no matter how hot your inside is. It may work longer but not harder.

You are correct in thinking that the heat rises in the summer so it naturally stays warmer upstairs and vise versa in the winter months.

However, it's not only your stairway that allows the heat to travel upstairs. It's the flooring and subfloor in your home.

If you close off the stairway there will be a noticable difference in temperature upstairs but not completly fix your problem.

The cheapest fix I can think of would be to either install a door in the stairway or an air door. The air door is just basically a fan that blows straight down and it does do a good job keeping the air seperated on both sides. You could also put in a window unit. That would help out alot. Just be sure to NOT put it close to your thermostat.

Before I got my central air fixed this year I put a window unit in my bedroom and a fan at the door blowing out. It made a huge difference in about half my house.

Those are the cheapest ways to help you out. There are better ways to fix your problem but it would involve $$.

Like upsizing your upstairs unit. Installing an attic fan. Re-insulating also but all that costs a pretty penny.

I hope some of this helps.

  That is something that never crossed my mind.

You're supposed to get a 12-15 degree temperature drop from what your return takes in and what your fan blows out I think.

So it would make sense to have your "hottest" part of the house draw air from the coolest. I'm no expert but that sounds good to me.

The only problem with that to me is....

You still have a "heat rises" problem. Maybe the walls in your finished attic has inadequate insulation.

I'd try your idea though about the return.

Just expect to do alot of work to get it done or be prepared to pay someone to crawl around in your hot attic.   Good luck