Does any vendor make a ridge vent that would only allow air to go out but
would close down if air came back in? I am trying to shape the airflow so
that air gets into an attic from cooler vents that are under the gutter, and
only hot escape air goes out the ridge vent.
While the idea is clear, I cannot locate any product that does it.
What do you see as the benefits to what you propose?
I know of no such animal for standard ridge vents.
The air movement through eave/ridge vents is by convection and at very
low pressure. There might be a miniscule Venturi effect if the wind
is blowing right. As such there's not enough energy inherent in the
system to operate a louver to open or close to shut off the air flow,
and a powered louver would have to be used. Considering the length of
the ridge vent it would be an expensive proposition. The closest
thing - and it's not very close - is a thermostat or humidistat hooked
up to a powered roof vent (they look like broad, low mushrooms).
< What do you see as the benefits to what you propose?
When we turn on an electric fan to vent air from the attic during the day,
it ends up using the ridge vent to suck air in. Hot air rises up the
shingles of the roof, so the air coming in from the ridge vent is super
heated air. You end up replacing hot air with hot air.
I would also like to close the ridge vent permanently during the winter.
The attic isn't well insulated, so letting hot air just freely escape during
winter probably lowers temperature in the main living space below the attic
faster than it would if we could trap hot air in the attic.
All of these things are interrelated and it's unclear where you are,
what climate you're dealing with, type of insulation, etc. The
shingles heat up and the air above them does heat up, but it is not
all flowing along the roof. Hot air, particularly "super heated" air
tends to rise rather quickly and not muck about. Unless you are
monitoring the incoming air, I think your mental model needs a bit of
modification as I would tend to doubt that the incoming air is all
that much hotter than the air that's already on the inside and right
under the shingles (assuming your insulation is in the ceiling).
There are a couple of ways to look at this. One of them is that the
fan you have now is pulling in too much air, and the other is that the
ridge vents are not large enough to exhaust the air on their own. But
ridge vents are not meant to exhaust hot attic air. They're there to
allow water vapor to exit without creating rot and condensation. Like
I mentioned earlier - unless you are monitoring the incoming air
temperature and volume, and comparing that to the exhausted air
temperature and volume you really don't have a handle on what exactly
is happening. But that's not necessary. The only question is if the
fan is bringing the temperature in the attic down sufficiently? If
not you could rig up some sort of mechanically or thermostatically
controlled louver to shut off the ridge vent, but that's going to be a
lot of work, cost a bit, and be a kludge unless you want to spend a
lot more money to do it up professionally.
Have you thought about installing some reflective insulation on the
bottom of the rafters to block more of the heat (and keep in more heat
in the winter) and increase the efficiency of the ridge vents? That
won't be cheap, either, but it'll be easier than the ridge louver
thing and probably a lot more effective.
That warm, moist air escaping the house into a cold attic will cause more
moisture problems than potential rain at the ridge vent. The warm moist air
condensing on the underside of the roof structure can drip onto the
insulation, and / or run down the rafters and damage ceiings..
It really sounds like you need to address better insulation in the ceiling,
and sealing any directs air leaks to the attic, if the house is getting heat
from the attic in summer, and heat is escaping to the attic in winter.
Also, an attic is normally vented quite well by flow from the eave vents to
the ridge. Check your eave vents for blockages.
None that I know of.
One way to do it would be to close in the rafters so that the only
openings in the attic would be the ridge vent and the soffit vents. You
can use sheetrock, rigid foam panels, or any other sheet goods,
including plastic vapor barrier to close in the rafters.
You don't think that natural convection won't be enough? I think why you
can't find what you are looking for is that it doesn't exist as there
is little need for it. (Not saying you don't have a need, just that it
is very rare that someone would want to force it...)
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