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).
RW wrote the following:
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...)
< 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.
R
Turn the fan around, blow into the attic and allow it to vent from the ridge vents...
Bad move, if you have snow it will ice-dam and that can (and will) cause leaks. You'd be much better off with an insulation upgrade to keep the heat out of the attic instead of trying to keep it in!
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.
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