I live in Smyrna, so I'm also getting the Atlanta summer.

The house was built in October 2002. It has ridge vents running the full length of it. All ducts are insulated. There is
blown insulation in the attic. The return ducts are on the attic floor and get some covering from the blown insulationas
well. The supply ducts are suspended overhead in the attic, so they only have the standard insulation around the duct.

The high temp in the attic is definitely causing cooling loss during the day, but the thing that concerns me is during
the morning, when I took the last set of measurements, the attic was only 74 degrees. The supply was 64 and the return
was 69, so the unit was dropping the temp 5 degrees with an attic temp of 74. When the attic temp was 110, it was
dropping the temp 7-8 degrees. This would seem to indicate that the unit can't cool air beyond 64 degrees. That seems
like a problem attributed to something other than cooling loss thru the ducts since the unit on the 1st floor drops it
17 degrees under pretty much the same conditions. The difference between the two units is upstairs is 2.5 ton and
downstairs is a 3 ton. That shouldn't cause the problem I'm seeing.

I didn't have this problem last summer. I have programmable thermostats set to the same schedule as last year. My power
usage this year for May increased 76%, June was 78%, July was 21%, August was 21%. July and August didn't increase as
much as May and June, but that is because the AC is running a lot during those last 2 summer months anyway, so there
wasn't really much more it could run. We started using the AC in mid April of this year. It's usage was 16% higher. The
months where we used heat only had an increase in usage of only 1%~2%. AC is running a lot more this year, and the
summer this year isn't really hotter than last year's.

The easiest thing to quantify out of all these numbers is that I know the upstairs runs a lot more. The fact that it
only drops the temp from 5-8 degrees upstars between return and supply is proof.

"Joe Fabeitz" wrote in message ...
Are the ducts in the attic insulated? How well? Two years ago I bought a
similar house (twenty years old) and immediately replaced both HVAC systems
and all of the attic duct work. Although the new systems kept up with
Atlanta summers, I chose to also add "radiant" insulation to the attic. The
result is the attic temp. is never more than 12 degrees hotter that the
outside temp. Something to consider.

"Brad C" wrote in message
...
I have a 2 story home with basement and my 2nd floor is not cooling like
it did last summer. This summer isn't really
any hotter than last year, but my 2nd floor unit runs a lot during the
day, and the thermostats are set to the same
values as last summer.

I have a few thermostats/hygrometers I use around the house and taped them
to the return/supplies in the master bedroom
to check the temp difference. When the attic was around 110 on a hot day,
the supply was blowing in air at 68-69 and the
return was taking in air at 77. I had a technician come out to inspect and
he said the 8-9 degree difference was due to
the heat loss in the runs in the attic. He quoted some degree per foot run
loss, but I don't fully buy it. He also said
they shoot for a 10-12 degree diff for 2nd floors and 15-17 diff for 1st
floors.

Today, I measured the temp diff around 8am when the attic temp was 74.
Supply was 64, return was 69. I have a 2.5 ton
unit for the 2nd floor. I had let the unit run for a half hour to make
sure the air was at its coolest.
For the downstairs, I had 57 from the supply, with 73 going in the return.
The basement temp was 75, so the ducts for
the 1st floor, which are in the basement, were roughly experiencing the
same amount of heat loss as those in the attic
( attic was at 74 ). The 1st floor unit is a 3 ton.

The house is almost 2 years old. The company that did the install
performed a flush/recharge on both units for free
since I'm still under warranty, and that didn't help.

So, I experienced a 5 degree diff when the attic temp was at 74. The
system was charged to the recommended level. The
technician came out 3 days after he flushed/recharged and checked the
system again.

The airflow seems to be fine. Any thoughts ?