I want to add a few more inches of blown-in insulation to my attic which
contains a 24" whole hose fan venting through 2 vents on the gable end
walls. I am concerned that this new insulation may be blown around & clog
the vents when the whole house fan runs if I do this. Am I worrying
<< I am concerned that this new insulation may be blown around & clog
the vents when the whole house fan runs if I do this. Am I worrying
Probably yes. To relieve your concerns, when the job is done turn on the fan
and spend some time up there with adequate lighting, of course. It may be
sensible to limit the impingement of the fan outflow on the insulation by
laying some low cost panelling sheets around the fan box. HTH
We used to have a monster whole-house fan in our 1930s Cape Code before
we finished the attic and had to yank it. The blades would make a fine
properller for some light aircraft, for sure, and boy do I miss that
appliance. Cooled the house in 1-2 minutes. Anyway, I'd think the answer
to your concerns would depend more on whether the air flow from the
thing is directed more sideways, toward the wall vents, or more upward
and into the attic space itself. If it has a more upwardly flow, you
*could* get some additional blow around, but it might be impossible to
know for sure until you actually put in more blow-in, crank up the fan,
and see what's going on. You might be OK if your fan is more
vent-directed, but again, you probably really won't know for sure until
you do it.
But if you do get blow around, you'd need to either dissipate or
redirect/deflect the strong air flow. To redirect or deflect (assuming
that the fan is somewhere near the wall with the vents, perhaps a 1- or
3-sided hood built from sheet metal and attached to the fan's outer
frame could be used to more fully deflect the air flow toward the vents
(and away from the blow-in). I'm not sure how you'd dissipate the flow,
especially if it seems like a tornado is dancing around up there as it
is when the fan's going. Perhaps a qualified HVAC guy can lend some
professional advice or assistance for that.
Thanks for your reply,
The fan sits horizontally on the ceiling joists directly above the louvered
opening in the upstairs hall ceiling. It draws straight up (from roughly the
center of the house) & exhausts through enlarged vents on the gable ends of
the house . (that are probably 3-4 feet off the attic floor)
There is presently about 4-5 inches of loose insulation up there.
That's pretty much how ours was set up and in pretty much the same
place, except in the ceiling along the short hall between kitchen and
living room. But if I recall right from 6-7 years ago, we didn't get a
lot of tornadic blow-around up there when the thing was cranking. We
have a Cape Cod with a steep pitch to the roof and had 1,000 sft of open
floor space, so there was about 10-12 feet of head room between the
interior peak and the fan, so the force of the air coming off the fan
was able to dissipate pretty well from what I remember. Was more like a
gentle breeze up there; didn't even budge the dust or either colony of
Big Brown bats in the screened-off peak vents about 8 feet off floor
level on both sides of the attic.
I'm inclined to think another 2-3 inches *probably* won't make a
difference, but again, that's just my inclination. I'm not a trained
professional, and I'd recommend anyone who's not 100% sure about
something to consult one.
I have a 30" whole house fan, mounted in a manner similar to yours. I have 15"
cellulose insulation throughout my attic (yes, I know that's overkill).
While filling the attic with insulation, I built a 24" high box around my fan,
cardboard and duct tape. Worked a treat.
Tim =(substitute 'tcsys.com' for 'nospam.co.uk')
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Had the same situation in my last house and it was no problem...what you
didn't mention though was how high the roof peak is above the attic floor.
Mine was a good 8 or more feet.
Just remember, you're creating PRESSURE in the attic not a vacuum, and that
tends to hold the insulation in place...not blow it around.
Thanks to all,
I would say the roof peak is about 7' above the attic floor. From what I'm
reading I think I should be fine adding a few more inches of insulation.
Has anyone rented an insulation blowing machine & done it themselves? (Lowes
has a deal that they don't charge for the machine if you buy 20 or more bags
of loose insulation)
I was wondering how hard it is to spray a fairly even layer?
Those machines work fairly well. I would get some goggles and a respirator,
though. The air will quickly become thick and unbreathable. The insulation
in the air will find its way through the attic access door as you are
blowing, but if you're blowing cellulose, it is not a problem to just
vacuum. Cellulose certainly won't make you itch all over. The insulation is
hard to keep out of soffit vents if you have them. Covering with a foam
baffle, sold in the same isle as the insulation, will make it so they don't
clog up, or you can blow the vents out from the bottom or vacuum from the
top, but I didn't want to walk through the new blown insulation so I elected
to use compressed air from outside. It's easier as a two person job. Have
someone stay by the machine to load new bales. Equip them with a box knife
to cut the bales. Instruct them what will happen if they stick their arm
into the hopper and the shredder grabs their fingers. In the attic, nail a
string line the thickness of the new insulation you want over the old
insulation. It will give you a guide as to how thick it is as you go along.
I put up about 6 string lines in a grid, and then could tell easily that it
was consistent across the whole attic. If you have projections through the
attic floor(vents, wires, etc.), now is a good time to calk around them to
reduce the air transfer. When you get done, turn the whole house fan on and
right back off. This will clear the fan, but not allow the gable vents to
become clogged with the airborne insulation. Let them settle before turning
the fan back on. you shouldn't have any insulation move when the fan is
turned back on. When you're done, make sure the attic access door has a good
seal. This is a good place for heat to leak out of the living space. Spend
some time to make sure it is tight. During the winter, the biggest air
transfer will be the whole house fan louvers unless you put plastic up, or
use a cover made for it. Don't assume they seal anything. They are pretty
much worthless for that job. they need something additional to insure that
it wont contribute heat to the attic.
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