Re: It's Hot Upstairs More Insulation or Attic Fan?

mm wrote:
On Sat, 05 Jul 2008 23:38:49 -0400, tnom@xxxxxxxxx wrote:

On Sat, 5 Jul 2008 12:20:37 -0700 (PDT), Tom in PA <vmcw@xxxxxxx>
wrote:

Hi!

We have a two-story home in Flagstaff, AZ. It's normally cool enough
around here that, without using our central air, the downstairs stays
pretty comfortable during the day if we open things up at night to
cool the house down. But the bedrooms upstairs get pretty toasty.
The attic gets very toasty, naturally. I'm thinking about either
adding insulation in the attic to keep that heat out of the bedrooms
or putting in an attic fan. The house is two years old.

Each bedroom has two walls and of course the ceiling that are adjacent
to the attic, so I can add insulation to both walls and ceiling.
Currently, the walls have fiberglass insulation between 2x6s and the
ceiling has roughly 6" of blown-in insulation. There are three gable
vents in the attic and a good number of 3-4" diameter vents on the
eaves.

So..... any suggestions? Will either the fan or additional insulation
make a significant difference in bedroom comfort? Any advice would be
appreciated!
Neither of your choices will do much to remedy your situation.

You say that downstairs stays cool enough that you don't use the central air. This means that there is no forced air circulation
during these time periods. Since heat rises it would be normal for the upper floors to be considerably warmer than the lower floors Since heat rises the heat in the attic will have little effect on the
floor below.

If that were true, why did putting the roof fan lower the temperature
of my second floor by more than 10 degrees? When the attic fan is
out of service, and the motor only lasts between 3 years and 10
years**, so it's out of service for a couple days when it breaks, and
I stand on a chair and put my hands near the ceiling, it's terribly
hot. If I were to do that when the fan is working, it would only be a
little hotter than at the 4 foot level. (I have 8 foot ceilings.)

Now maybe I could benefit from more insulation in the attic (i have
one or two inches of cellulose plus one batt) but it's still not ture
that because heat risess, the heat in the attic will have little
effect on the floor below.

**It's amazing to me that some motors lasted only 3 years and others 7
to 10. I first sent away to the fan maker, but now I just buy new
ones at the motor shop in town.

Most all of the heat on the upper floor is from lack of
circulation. Do not let stagnate air laminate into temperature layers.

My comparisons are drawn with no AC in both situations. The only
difference is whether the fan in the roof is running or not.

You are correct, especially after dark. That big mass of superheated air and building materials called an attic, radiates heat back into the 2nd floor until well after dark. Keeping attic vented, and adding insulation to provide a thermal barrier, does a lot to keep the 2nd floor cooler. Even in this one-story house, I noticed a big difference after adding more attic insulation and improving the attic venting. I don't have to immediately set the a/c on full when I get home from work anymore, and ceiling is no longer warmer than walls to the touch.

--
aem sends...
.

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