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Solar Attic Ventilation in Florida

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Posted by Dave Saxton on June 19, 2006, 11:33 pm
Hello. I live in central Florida and was looking for ways to help curb
some of my high electric bills. I have switched over my lights to the
energy efficient types and am looking for other ways to conserve. My
A/C seems to run all of the time. I keep it set at 78-79 on most days.
I was looking into the possibility of solar-powered attic fans to go
into the gables in my roof. However, I read somewhere that this might
not be the best thing to do because I would essentially be pulling
more humidity into my attic and increasing the possibility of mold and
other such issues. Does anyone have any information on this or maybe
could offer some other insight?  My next step is to find out more info
about my hot water heater and I also have a pool pump that runs about
8 hours a day. Any suggestions for those would be helpful as well.

Go easy on me... I'm a newbie at being green :)


Posted by BobG on June 20, 2006, 12:53 am
A professor somewhere has a web page that says you need enough CFMs to
change 50% of the air a minute. Its easy to compute the cu ft in the
attic... area of a triangle is 1/2 base x height. Volume is area x
length. Go to Skycraft corner I-4 and Fairbanks in Winter Park and look
at the 12V fans. Maybe the harbor freight 45W solar panels could run 2
or 3 12V fans.

Posted by Solar Guppy on June 20, 2006, 12:57 am
 If your AC is running all the time set at 78, your insulation must be nill

I'm in central Florida and even in the 90+ days, the AC only cycles about
25-30% on in the mid afternoon heat, 10 year old house. You should have R30
minimum in your attic, about 12" deep... It's cheap to have a company come
and blow in fiberglass around here , typically 500.00 to get you back to
R30+, that should be your first priority as its probably about 80%+ of your
bill if your AC is constantly on

As for the vents, you should have either ridge or covered vents already,
that naturally draw in air from the soffit which with proper insulation is
all that is needed for proper ventilation. One also not be adding more ways
for wind driven rain to enter the attic, pretty common issue here with our
common storms

Posted by Dave Saxton on June 20, 2006, 2:06 am
 That seems pretty reasonable. We purchased this house in August 05. It
was built in 1981, and the A/C unit is the original. There is a bunch
of white insulation that covers the entire attic. It is loose, not the
rolled out pink panther stuff I have seen at Home Depot. However,
underneath the white stuff is the pink panther stuff. Does that make
sense?  I have 3 gable openings in the attic as well as an opening
that goes along the very top of the roof at the peak. It's covered on
the outside. I forget what kind of vent the home inspector called it.
I also thought the ventilation was okay. The thickness of the pink and
white insulation together is only about 6-8 inches, so that is
probably where the problem is. The A/C tested okay and part of the
contract was to have the unit inspected and serviced. I am wondering
if it is time to get a newer, more efficient unit?

Thanks for the input!

On Tue, 20 Jun 2006 00:57:20 GMT, "Solar Guppy"

Posted by Solar Guppy on June 20, 2006, 3:14 am
 Most new construction (Florida) is the blown in Fiberglass ( white fluffy
stuff ) , you want this as deep as possible ... I went R40 on the home I
built ( previous house ) and that's about 14-15" , current code is R30, back
in 1981, there was NO code requirement and I have seen a few homes your age
with next to nothing

Sound like you have plenty of venting, the vent is called a ridge vent and
allows the hot air to exit at the very top of the roof, which draws in air
from the soffits and or gable ends ... that's fine. Fans actually can be
VERY bad, as they can make a negative pressure and suck the cool air out of
the living space thru vents/holes  ect.

Since you home is 25+ years old, I would also be very suspect of your A/C
duct-work ... my guess is you have holes/tears and your just sending the AC
into the attic , its not a great time to do this ( summer) but you should
have a professional do leakage tests on your duct work or visible inspect

Also, your unit is probably only a SEER 6 to 8 best case , today's systems
are code minimum 12 to as high as 17 ... a SEER 6 will use twice the
electric as a SEER12 to give you an idea

SO, if it was my home, check the ducting, get fiberglass blown in deep
enough to cover all the ductwork ( 500 -1K), replace the AC with a SEER 14
(5-7K)  mid priced , more than 12, but not as much as a 16/17 ... all
together, probably about a 6-8K work of work and probably drop you bills by
70%, if you do only one thing, get the fiberglass blown in as deep as you
can afford

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