Keeping a multi-story house cool using AC and attic fan?

[Martinjmpr]

Thanks to some suggestions here were had a very nice 3.5 ton central AC unit installed back in March. After our brutal Summer last year I felt we had to do something.

Now I'm looking for tips/tricks/suggestions on the best way to use what we have.

Here's our situation: We have a 40 year old house that was not originally built for AC. It is reasonably well insulated for a house that was built in 1979. It's located in the Columbine area, near Columbine HS so those of you who are familiar with the area can probably figure out what general type of house it is.

The house is a tri-level with a finished basement (so basically it has 4 levels.) The basement is finished as an extra bedroom but we mostly use it for storage.

Other than the basement, the lowest level is the "garage level" which includes the family room, where we spend most of our time when we are not in bed. Next level up (about 5 steps) is the kitchen/dining/living room, and then nearly a full level up (let's say 15 steps) is the "bedroom level" with 3 bedrooms including the master and 2 baths. My office is one of the upstairs bedrooms.

Our house faces to the South but doesn't have a lot of windows on the South side except upstairs. The garage faces South and the garage door and garage walls are fully insulated.

The new AC unit does a wonderful job of keeping the two "main" levels cool, i.e. the family room and the kitchen/living/dining room.

It does less good at keeping the upstairs cool, and the issue there is that 2 days a week, I work from my my office upstairs.

The house originally had an attic fan, which it sill has.

What we have been doing lately (still experimenting) is this: At night, AC is OFF and windows are open. If it's cooler outside than inside, we run the house fan to pull cool air outside and into the upstairs. Usually it is reasonably cool in our bedroom by the time we go to bed at 10:30 or so. We have a small floor fan in the bedroom which runs all night to keep air circulating. Windows are open in the bedroom, my office, and downstairs to let cool air in.

We shut off the house fan at night because the wife doesn't like the noise (personally I'd like for it to run all night, I don't mind the "white noise" but, "happy wife, happy life", right?)

In the morning, windows stay open (especially the windows downstairs) and we leave the AC OFF and turn on the house fan, again to pull in cool air.

About 10:00 or so, when it starts getting really warm outside, house fan is turned off, all windows get closed and AC is turned on. In addition, if I'm working in my office (which is on the West side of the upstairs), I shut the blinds and the curtains.

We generally leave the windows closed and the AC on until it starts to cool off outside - say, 7:00 or even 8:00 if it's a really hot day. Once it's cooler outside than inside, we shut off the AC, open the windows and turn on the house fan.

So does this sound like a good plan? We have only just started and as I said, we are still kind of experimenting. Just looking to see if there are any tips or tricks anyone else can suggest.

Right now the biggest issue for me is that it still gets very hot in my office in the late afternoon when I'm working. Wife is usually downstairs so she doesn't have any issues with the upstairs heat.

[.455_Hunter]

Why is it not working in your office? Low flow? Insufficient vents?

If one of the above, I would get an inline duct booster fan installed for force more flow into that room.

The window/house fan regimen you describe is why you install AC in the first place- make your new AC system work for you.

[ray1970]

I?m in a similar situation. Four levels. If I try and keep the upper level cool the bottom level is like a meat locker. If the lower levels are kept comfortable the upper level can be a little toasty.

I?ve been kicking around ideas for an attic fan. My preliminary plan is to use the attic fan in conjunction with the AC to pull cold air from the lower levels to the upstairs.

Let me know if you come up with a solid working plan.

I haven?t installed the attic fan yet so my ideas are simply ideas.

I do the vents different for summer and winter and that helps a lot for now. I close the vents on the bottom two levels when the AC is on and force the cold air to the upper two levels where it?s needed the most. In the winter I shut the vents on the upper levels and force the heat to the bottom two levels and just let the heat rise to the upper levels. This has worked well for me for now and forcing the cold air to just the upper levels has kept the upstairs nice until I can get around to installing the attic fan.

[ray1970]

I?ve also considered moving the thermostat to a different level of my house.

[Mercula]

Youre doing almost exactly what Im doing with the similar set up but only two stories above ground. I however do not have central air and have installed multiple window units. Can I add a question to your question ? how much of the cooler air do you think descends down to the basement making the basement even cooler leaving the upstairs floors warmer? I was tempted to hang a heavy curtain or something going to the basement to See if it kept more cool air upstairs.

My living room ceiling is vaulted up to the second floor, I do have a ceiling fan hung on a drop in the living room and have noticed it most definitely keeps the temperature more consistent between the two floors with that fan running circulating between my first floor and my second-floor essentially.

[Jamnanc]

I use a portable swamp in my top story. Keeps cool and massively reduces my energy bill.

[newracer]

Does your HVAC controller have a "circulate" function? If it does it should help keep the entire house the same temp.

[DenverGP]

My house is a ranch layout, with a finished basement. Even with all the vents in the basement closed, it gets much colder than the main floor when running the AC. I did add a heavy "blackout curtain" at the bottom of the stairs to try to limit the cold air from just flowing downstairs.


The only return air vents for the house are on the main floor. I've thought of adding some return vents to the basement, and blocking off the main floor return vents during the summer, and blocking off the added basement return vents during the winter. Seems like that would let the "circulate" function re-distribute the conditioned air better.

[Martinjmpr]

After walking around in the living/dining rooms (which we rarely use, especially in Summer) I realized that the 3 vents were open in those rooms, making them very cool. I immediately closed all 3. Currently showing 76 in the kitchen (which is the hottest room on the main floor) with 98 outside.

I may try to close ALL the vents on the 2 main floors to force the cool air upstairs.

[Martinjmpr]

Does your HVAC controller have a "circulate" function? If it does it should help keep the entire house the same temp.

By "controller" do you mean the thermostat? If so, I don't think it has such a setting.

Question: It does have both "on" and "auto" fan settings. If I set the fan to "on" would the AC unit (i.e. the chiller) run constantly or just the fan? Seems to me if I can set it to where the fan runs but the chiller only comes on when the temp drops below a certain level, that should help even out the temp in the house, right?

Then the next question is, is the fan a big power draw? I know the chiller is.