Best approach in general to a hot upstairs?

[SecondCor521]

Followup and some additional responses:

I bought and installed one of these:

https://www.lowes.com/pd/QuietCool-QuietCool-Smart-Attic-Gable-Fan-AFG-SMT-ES-3-0/5001584785

in the gable vent that is on the north side of the house which also happens to be pretty close to the peak of the roofline.

I really like it and I think it's working quite well. I can't hear the fan at all in the house when it's on. The past day or two has been relatively cool outside, but the attic still got up to 110 degrees or so. I chose default settings, so the fan was on low for several hours, then medium several hours in the mid-afternoon, then presumably low and then off again in the evening.

Even on high, the fan uses something like 148 watts, so really quite low I think? This model also has a nicer motor on it and comes with a 7/3 warranty so I'm hopeful it should last quite a while.

Normally the AC would come on for several hours during the day, but yesterday it was only on for about 10 minutes or so. I'm hopeful the fan is a net positive.

On other stuff people have mentioned:

I already insulated the attic area to about R-60 several years ago. At that time I also checked all the vents for air leakage and made sure all of the attic intrusions (like around ceiling lights etc) were properly insulated.

Floor between FROG and garage was confirmed to be insulated.

There is a return in the FROG near the apex of the ceiling and it is unimpeded.

...

I've read about them but I honestly don't think the idea of whole house fans would work around here. In the case of my house, it's basically a two layer cake - first layer is air conditioned space at about 70 degrees, and second layer is the attic which is not conditioned space and before the attic fan was maybe 120-130 degrees. Outside high today might be 80 degrees. Maybe I'm misunderstanding something about whole house fans, but I'd much rather have an attic fan replacing 120-130 degree air with 80 degree air than a whole house fan replacing 70 degree air with 80 degree air.

I do sometimes open downstairs windows and upstairs windows and let the house self ventilate if the outside air temp is going to drop to 50 - 60 degrees overnight, so that seems like sort of the same idea.

...

I have the HVAC fan off when my son is gone during the day at work because I don't like the background noise. When he comes home he can turn it on to help circulate the air more.

Between the HVAC fan on and the attic fan with default settings, it seems our problems there are essentially solved to at least my satisfaction.

I do have a note to check my electric usage in about a week to see if I'm actually getting any noticeable savings. If I remember to and if it's significant I'll post an update here on that.

Thanks all.

 

[Badger]

When I built a 1600 sq ft house in the mountains the second floor was 2/3 the size of the first floor and open to the first floor at the living room on one end. The hot air would rise and make the second floor hotter. I put a floor register at the far end on the second floor opposite to the living room with a duct to the first floor and a fan to pull the air to create a circulation. It worked well to stabilize the temperature throughout the house.

 

[sengsational]

Single zone multi story houses should have a vertical duct with a sensor at both ends. When the temperature difference gets big enough the fan should come on, pushing hot air into the cooler zone and triggering the A/C through the single thermostat. But a long vertical chase might be against fire code.

 

[Ronstar]

In our first house, I put in an attic roof mounted vent fan, and a whole house fan. Cooled the upstairs and the attic.

The motor of the attic fan eventually burned out. But the whole house fan still cooled both the upstairs and the attic. The whole house fan sucked air from the basement up through the upstairs and pushed it out the attic through the roof vents and soffit vents.

 

[mf15]

My guess. Poor return airflow/not enough cooling flow. Block off some downstairs return vents with printer paper and tape, until strong upstairs return vent flow, close down downstairs cooling vents somewhat. The idea is to increase upstairs cooling flow,and increase hot air return.