Replies

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   Guest_ | Feb 19, 1999 04:43am | #1

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   Mike, unfortunatly, this one of those ideas that seems to make perfect sense, but often not only doesn't work, but makes things worse. A house the age of yours and in a reletivly mild climate will most likly have lots of air by-passes between the house and the attic. If you run the attic fan in the heat of the day, some outside air will be drawn in through other vents, but also much house air will be drawn into the attic, which will then be replaced by hot outside air. So, you will probably wind up cooling your attic a bit while at the same time you heat your house (and burn electricity into the bargin). The best solution to block attic heat is good insulation. In your climate a whole house fan run during the evenings when it is cool is often very effective.

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   Guest_ | Feb 19, 1999 06:57am | #2

   *J.T. What we really need is a way to cool the house in the evenings. The outside temperature always drops down to a comfortable 65 and we suffer till 2:00 am with an 80-90 degree house. My thinking was the hot air in the attic was acting like an oven above us. Maybe I'm wrong. Advise if you

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   Guest_ | Feb 20, 1999 04:15am | #3

   *Mike, your quite right and if you are planning to run a fan evenings only, it would be fine. Most attic fans come with a thermostat that runs it when attic temp. is high i.e. during the day and part of the evening. Since you're really talking about a whole house fan concept you may want to go that way as opposed to gable vent fan. The advatage of a gable fan when used this way is that it doesn't pressurize the attic. The disadvantage is that you won't be able to get nearly as much air flow as with a ceiling mount. Either way, you will need to provide an opening in the ceiling so that you can control how the air flows into the attic. If you don't, a gable mount fan will suck air out of the house through all kinds of accidental paths, which can cause dirt stains to appear in various places such as at the edge of carpets where air can be pulled into the attic through the gap at the floor beneath drywall (there was a discussion somewhere on this board about that type of stain).If you go with a ceiling mount fan, some care must be taken to provide adequate attic vent area other wise the fan won't be able to move it's rated air volume. Assuming that the fan can provide .1 "wg of static pressure (a typical rating), you would need a minimum of 1 sq. ft. of net free area per 750 CFM of fan capacity.One final note. In either case you'll need to be concerned about combustion appliance safety. While you probably won't be running the furnace, if you have a gas water heater or stove, you don't want to backdraft them. Just be sure to keep some windows open when ever the fan is on.

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   Guest_ | Feb 21, 1999 09:30pm | #4

   *Or, the Q&D solution -- open lots of windows to encourage cross-ventilation. Strategically place a few good-quality fans (we have a couple of the small commercial-style metal cage fans, skip the plastic) blowing out windows towards the lee. Easy to control, remarkably efficient, easy to fine tune -- and you know where the replacement air is coming from.We have the same problem you do, with the house 10-20° above ambient in the evening -- very annoying to use -any- energy to fix it when plenty of comfortable air is close at hand. Where you live (a nice place, my grandmother lives up there) the sun is quite intense, good for the grapes I guess. The gable vent fan would be a band-aid (one that we are using at the moment! but I'll decommission it when I can rework the falling-down insulation in the rafters to keep more of the sun's heat at bay. Even the fiberglas batts which haven't fallen make a BIG difference, as I have noted crawling the hot and sweltering spaces in the attic.