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Home > Archive > Alternative Power sources > September 2006 > Attic fans
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| John Dunkley 2006-09-12, 3:25 am |
| I am wondering if anyone has personal experience with attic fans?
i.e. pumping hot air out of the roof space/attic during summer?
Would be interested to know if it is worthwhile.
JD
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| barry@sme-online.com 2006-09-12, 1:25 pm |
|
John Dunkley wrote:
> I am wondering if anyone has personal experience with attic fans?
>
> i.e. pumping hot air out of the roof space/attic during summer?
>
> Would be interested to know if it is worthwhile.
>
> JD
Works fine for me. With t-stat set to make @ 110F, it keeps floor below
measurable cooler than without it, at peak summer temps. That floor
peaks about 5deg F lower. In cooler periods, it works well as
whole-house ventilator.
Mainly, it keeps attic temps from literally roasting rafters, and, of
course, shingles. Anticipate it'll greatly extend roofing
life-expectancy.
In my case, passive ridge vent was not practical.
J
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| Harry Chickpea 2006-09-12, 1:25 pm |
| "John Dunkley" <jedunk@REMOVEbigpond.net.au> wrote:
>I am wondering if anyone has personal experience with attic fans?
>
>i.e. pumping hot air out of the roof space/attic during summer?
>
>Would be interested to know if it is worthwhile.
>
>JD
>
Powered ones are a waste of money that is better spent on increasing
the attic insulation. Passive ones, like roof turbines, can
eventually pay for themselves with lower roof temperatures. While the
primary limit to roof life is ultraviolet light getting to the
tarpaper and shingles, another factor is the heat of the roof creating
outgassing of the roofing felt and roofing, causing it to become
brittle and break, thus creating leaks.
My current house had concrete shingles over roll roofing, with no
vents other than soffit vents. Even though the roll roofing on it was
never exposed to ultraviolet after the installation, it began to leak
after about 20 years. I scrapped the cement shingles and re-roofed
with standard asphalt shingles and had a couple of roof turbines
installed.
The (loose cellulose) insulation had settled some over the years, so I
noticed an immediate effect with the change. Prior to the re-roof,
the house heat would lag the day on sunny days - little cooling would
be required before about 1 PM, but from then until long after dusk,
the AC ran fairly constantly and the house was warm. Even though they
were white, the cement tiles absorbed and held the heat from the sun,
and the attic acted as a reservoir of that heat.
After the change, the turbines slowed the buildup of attic heat enough
to slow the need for the AC until about the same time - maybe
half-an-hour earlier, but then they continued to exhaust the worst of
the heat all through the afternoon and, more importantly, at dusk.
Instead of the AC running well into the evening and the house being
uncomfortably hot until as late as 10 PM during midsummer, the attic
cooldown was complete even as the sun was setting, making the evenings
much more comfortable.
I have since added automatic sprinkling on top of the roof to cool it
further during certain seasons. In early summer, the sun here is
constant and almost directly overhead, and wetting the roof cools it
significantly, saving electricity for cooling, and I believe extending
the life of the roof. There are naysayers that don't think cooling
the roof extends the life, and some of them can be quite nasty in
their denouncing of the practice. To them, I extend a heartfelt "piss
off and deal with it." It is my roof and so far I'm not seeing the
checking and cupping that I would otherwise expect to be seeing about
now.
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| > John Dunkley wrote:[color=darkred]
============================
The 'theoretically most effcient' algorithm is: change half the air
every minute. Ex: 1000 cu ft in attic, need 500 CFM on the fan.
| |
| nicksanspam@ece.villanova.edu 2006-09-12, 1:25 pm |
| BobG <bobgardner@aol.com> wrote:
>============================
>The 'theoretically most effcient' algorithm is: change half the air
>every minute. Ex: 1000 cu ft in attic, need 500 CFM on the fan.
How do you figure 'theoretically most effcient'? I'd say more is cooler.
Nick
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| Jim Baber 2006-09-12, 1:25 pm |
| Jim Baber wrote:
John, there are also "wholehouse fans" for you to consider as well.
If you are not familiar with them, they are installed in the ceiling
below the attic near the center of the house, and pull warm air from the
living areas and push it into the hot attic thereby forcing that hotter
attic air out of the attic.
These fans are very effective if the inside air is warmer than the
outside air, but they do require that you open windows or provide
another source of outside air in the living areas.
John Dunkley wrote:
>I am wondering if anyone has personal experience with attic fans?
>
>
My wholehouse fan reduces the need for air conditioning by about 6 hours
a day in 100+ heat and 10 hours in 90 - 99 heat, and eliminates A/C
below 90 when I am trying to maintain a 79 degree temp. in the summer in
Fresno CA. It works this well, because of our usually low humidity.
The nights usually are below 80 after 9:30 - 10:30 even on most 100+ days.
>i.e. pumping hot air out of the roof space/attic during summer?
>
>
It requires that you also have very good attic venting, I have 3
turbines and several regular regular vents. I have found that
occasionally on very hot days if I run the wholehouse fan for a short
time occasionally, it helps by forcing the super hot air from the attic,
but that means I am pulling hot outside air in from the window (I just
open one window near the fan), and that does not upset the general
inside temperatures, but does cool the attic just like an attic fan would.
>Would be interested to know if it is worthwhile.
>
>
Without a doubt. I am very sensitive to the temperature, and my health
is such that I require A/C in the summers here. (this year beginning
Jun 15 for the 90 days ending yesterday we averaged 99.5 degrees F. at
5:00 PM) I was reasonably comfortable keeping the temperature in my
house below 80, and yet I kept my actual a/c usage to a minimum.
>JD
>
One thing I might mention, I cool the house as much as I can in the
mornings before it gets hot outside using the wholehouse fan and even
the a/c, BUT, then after noon or if the temperature outside goes above
79, I close all windows and shut everything off until after 6 PM.
I am on what PG&E calls Time Of Use metering, for the power I use. That
means for the summer weekdays between noon and 6 PM, I have to pay 3
times much for "Peak" power than what I pay for all the other "Off Peak"
power we use. PG&E's obscene rates are why I have invested in solar PV
to the extent that I have.
| |
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| nicksans...@ece.villanova.edu wrote:
> How do you figure 'theoretically most effcient'? I'd say more is cooler.
=============================================
I read this on a website... some professor in Texas... but we ought to
be able to calculate it... given attic temp 150 deg F, outside temp 95
deg F, R value in ceiling 30, house temp 75 deg F... changing half the
air every minute reduces the temp diff by half... doubling the CFM
would only reduce it further by a quarter? Now does the fans with that
CFM use more watts than the AC would use to move the BTUs? (you're
better at R calcs than me Nick....)
| |
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| John Dunkley wrote:
> I am wondering if anyone has personal experience with attic fans?
>
> i.e. pumping hot air out of the roof space/attic during summer?
>
> Would be interested to know if it is worthwhile.
>
> JD
>
>
They've recently been pretty much discussed to death here and at
alt.home.repair .
Google is your friend.
--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.
| |
| Solar Flare 2006-09-12, 8:26 pm |
| I burnt out two of them in five years. I finally put a proper natural
vent in the hole and it works much better with hot air as it rises
naturally.
These new natural vents are so smart they know when to vent and when
not to. They have the intelligence to know the difference between hot
and cold air, somehow. I know this is a new concept but it can work.
"John Dunkley" <jedunk@REMOVEbigpond.net.au> wrote in message
news:H9tNg.27655$rP1.10734@news-server.bigpond.net.au...
>I am wondering if anyone has personal experience with attic fans?
>
> i.e. pumping hot air out of the roof space/attic during summer?
>
> Would be interested to know if it is worthwhile.
>
> JD
>
>
| |
| John Dunkley 2006-09-12, 9:25 pm |
| Can you give me a pointer to the type you are using please?
JD
"Solar Flare" <solerfart@hotomali.invalidated> wrote in message
news:D8GdndZxmfIJx5rYnZ2dnUVZ_rWdnZ2d@golden.net...
>I burnt out two of them in five years. I finally put a proper natural vent
>in the hole and it works much better with hot air as it rises naturally.
>
> These new natural vents are so smart they know when to vent and when not
> to. They have the intelligence to know the difference between hot and cold
> air, somehow. I know this is a new concept but it can work.
>
>
> "John Dunkley" <jedunk@REMOVEbigpond.net.au> wrote in message
> news:H9tNg.27655$rP1.10734@news-server.bigpond.net.au...
>
>
| |
| Solar Flare 2006-09-13, 3:25 am |
| hmmmm.... two of the most popular Broan and Newtone.
"John Dunkley" <jedunk@REMOVEbigpond.net.au> wrote in message
news:OMJNg.28008$rP1.12977@news-server.bigpond.net.au...
> Can you give me a pointer to the type you are using please?
>
> JD
>
> "Solar Flare" <solerfart@hotomali.invalidated> wrote in message
> news:D8GdndZxmfIJx5rYnZ2dnUVZ_rWdnZ2d@golden.net...
>
>
| |
| Sorobon 2006-09-15, 1:25 pm |
|
"John Dunkley" <jedunk@REMOVEbigpond.net.au> wrote in message
news:H9tNg.27655$rP1.10734@news-server.bigpond.net.au...
>I am wondering if anyone has personal experience with attic fans?
>
> i.e. pumping hot air out of the roof space/attic during summer?
>
> Would be interested to know if it is worthwhile.
>
> JD
>
>
I installed an attic fan in my house in Spokane, WA it dropped the attic
temp. from 120 to 100. That had to have an effect on AC costs. In 2 houses
in the Southwest I installed vents that allowed the air from the roof swamp
cooler to be vented through the attic rather than out the windows.
| |
|
| Sorobon wrote:
> I installed an attic fan in my house in Spokane, WA it dropped the attic
> temp. from 120 to 100. That had to have an effect on AC costs.
==================================================
If the fan was 200W and ran 5 hr a day, thats 1KWhr.... 15 cents a day.
3 ton AC 36000 BTU 10.5KW running 25% of the time for 24 hrs would be
63KWhrs... $9 a day.
AC only has to throttle back about 2% to make that up.
| |
| John Dunkley 2006-09-15, 8:25 pm |
| Now that is very clever!
JD
"Sorobon" <Sorobon@AOL.com> wrote in message
news:450ad7ef$0$9093$a8266bb1@reader.corenews.com...
>
> "John Dunkley" <jedunk@REMOVEbigpond.net.au> wrote in message
> news:H9tNg.27655$rP1.10734@news-server.bigpond.net.au...
>
> I installed an attic fan in my house in Spokane, WA it dropped the attic
> temp. from 120 to 100. That had to have an effect on AC costs. In 2
> houses in the Southwest I installed vents that allowed the air from the
> roof swamp cooler to be vented through the attic rather than out the
> windows.
>
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