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If you're asking if it will vent the hot air- yes. If you asking if it will lower the utility bill-no. You'll need a radiant barrier for that. In testing by Building Science Corp, they have shown many times in models and in actual homes that providing maximum ventilation buys you little. A sealed attic system where the air is not allowed to vent at all and with a radiant barrier will reduce utility bills substantially. With max ventilation, a laser temp probe will show the same attic insulation temps, with or without the vents. Some of the builders have integrated this into their building methodology and are now guaranteeing the max utility bill for a specific house plan. So far, it's working with most coming in lower than expected. Ryland was the first in our area with their EFL series of homes.
This is an interesting concept. I like watching those home improvement shows, and I'm surprised I haven't seen a radiant barrier installed.
Location: Visitation between Wal-Mart & Home Depot
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Quote:
Originally Posted by K'ledgeBldr
Apparently you don't understand fluid dynamics.
Convection cooling relies on temperature indifference. A power roof ventilator creates positive displacement ventilation regardless of temperature.
The "con" of a power roof ventilator is- it's mechanical! Definition: it will fail.
A convection system won't fail- but it doesn't always "work".
While fluid dynamics, particularly gas dynamics as they relate to one's attic, has not been a major component of my training or profession, through the coastal Texas lens you are going to have convection in your attic when the sun is shining as long as you have a hole at the ridge of the roof and holes in the soffit. If the shape of the roof is right, the volume of air changed per hour can be as good or better than a powered unit on a thermostat. That's what I was gettting at.
Has anyone added soffit vents and a ridge vent to their home? I'm curious if these two items improve ventilation and allow hot air to escape from the attic?
People normally don't "add" soffit vents and ridge vents. An attic built without these things normally would have gable vents and/or roof vents (passive or mechanical).
Too many/too large vents could prevent convection and cause the attic to accumulate stagnant air, similar mechanics of a chimney flue being too large to vent exhaust gases before they cool but, in this case, preventing the venting of moist hot air (think of a glass of cold water on a hot day).
That's the thing though. I don't understand how soffitt vents draw in air effectively on days where there is little to no wind.
Certainly wind will help but the main action here is heated air want to rise. Even on cold days the heat from your home making it's way into the attic is going to heat air and it will rise to the top and out of the roof vents. That air is replaced from the vents. It's not a fast action but constant, it may not work as effectively in the winter time but you're just trying to expel any excess moisture. In the summer time it's very effective because the temperature of the air inside the attic is very hot compared to outside air.
I give you an example from domestic hot water coils in solid fuel boilers. You can take a very short piece of pipe of just a few feet and loop it through a small wood/coal stove. You connect the one end to the top of hot water heater and the other end to the bottom. It may take overnight but it will heat up 40, 50.... 100 gallons of water. There is some caveats here, the top of the heater needs to be well above the coil and very close to the heat source with as little bends in the pipe as possible.
People normally don't "add" soffit vents and ridge vents. An attic built without these things normally would have gable vents and/or roof vents (passive or mechanical).
Too many/too large vents could prevent convection and cause the attic to accumulate stagnant air, similar mechanics of a chimney flue being too large to vent exhaust gases before they cool but, in this case, preventing the venting of moist hot air (think of a glass of cold water on a hot day).
Actually, I've been amazed by how many houses/buildings I've run into that have absolutely NO attic ventilation.
The worst was a fairly new residential boys' home. About 6,000 square feet, single level, with 22 individual bedrooms, 4 bathrooms, a large kitchen & dining hall, and group room. The kitchen exhaust, and all 4 bathrooms vented (by blower) into the attic, which had absolutely no venting of any sort. Unbelievable!
What do you suppose the total bill was for THAT debacle - complete with replacing moldy insulation?
But I would like the upper level of my home to be more comfortable during the summer season.
How does the insulation look inside your attic? Some observations I've noticed on my house:
Built in 1954. Attic has small front gable vent, 2 additional vents on the roof, and powered gable fan on the back. My insulation is VERY inadequate, barely covering the ceiling joists in most places. These past few days, the temperature in good old Pittsburgh has been 90+ degrees. When the attic fan is on, the upstairs of my house will be about 78 degrees while the downstairs is set to 74 degrees during the day. The one day I accidentally turned off the fan switch (it is regulated by thermostat in the attic, but the previously replaced fan was not, hence the switch for it), the temperature was 83 upstairs while the downstairs was 74. The gable fan moving hot air from the attic prevents some heat from radiating through the ceiling into the living space. Once I get better insulation installed, my hope is that there will be even less radiation through the ceiling.
I'd like to take advantage of natural air movement by installing a ridge vent and soffit vents, but the work involved would be very costly and not probable right now.
My point has been if you want a few degrees cooler in your upper level, investigate the insulation side of things. It may help to have better insulation. However, proper venting and air movement in the attic will extend the life of your roof and prevent mold build-up.
I'd like to take advantage of natural air movement by installing a ridge vent and soffit vents, but the work involved would be very costly and not probable right now.
One thing to remember is the air is going to take the least path of resistance. If for example you install a roof vent near a powered fan it's just going to suck air out of the roof vent negating the benefits of both.
Please do not allow some contractor to tell you that you do not have to remove the old soffit.. Mine was plywood and I had already taken down some of it. Mike said it was not necessary to take it down that the new soffit would cover it up ... My point exactly..WE did take down every last piece. Use full vent soffit to get the most air flow from the soffit to the ridge vent.. this way the air will flow up each joist bay and the over all effect will be better - The guys that did the house next door did not take down the original plywood soffit that had a 2-3 inch cut out in the middle They put up the new full vent soffit over it... Easier to do and she did not know the difference...
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