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To attic fan or not to attic fan... that is the questions
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Posted by dcislander (My Page) on Mon, Oct 5, 09 at 19:11
Hey there all,
In the middle of a complete remodel of an older beach house: about 1200 sq ft, single story, no basement (2' crawlspace), and an attic that is mostly trusses and framing. The attic space gets brutally hot in the summer. The previous owners had an attic fan on a temp switch set to turn on at 90 deg, but like everything else, they put in the cheapest unit they could find and it sounds like a jet is taking off in the attic. I am getting mixed answers from different folks about the need for an attic fan. Some are telling me that the fan will suck all of the conditioned air up out from the home through all of the crack, spaces, openings... in the ceiling (sealing those is another HUGE project for another time). Other say that the fan will vent out the blazing hot summer air and help keep the interior cooler. If we do decide to go with a fan, I want to replace the one I have with a more quiet model, but I am not sure we even need it. What are your thoughts and experiences? Thanks for any insight. |
Follow-Up Postings:
RE: To attic fan or not to attic fan... that is the questions
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| Knowing where you live, the amount of attic insulation, and the type of HVAC system would avoid a lot of off target advice. |
RE: To attic fan or not to attic fan... that is the questions
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| Sorry. House is in Delaware, 8 blocks from the ocean. Decent amount of attic insulation--mostly bats down between the trusses. I would like to add blow in one day, I would say about 95% coverage. The ceiling is not completely sealed, ie the spaces around the recessed cans, plumbing, small holes, etc. HVAC is a 3 ton Geothermal unit. House is not very shaded and it gets hot up there. House is one big central living room/dining room/kitchen with two small bedrooms and a bath on each side (4 BR total). No basement, just a small crawl. Any other info you need? Thanks for any advice. |
RE: To attic fan or not to attic fan... that is the questions
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| The concern would be the possibility of drawing moisture from outside and from the house into the attic. Sometimes the best solution is more insulation between the rafters or a radiant barrier. |
RE: To attic fan or not to attic fan... that is the questions
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| Most things I've seen say they don't save energy, even though they lower the temp somewhat. The problem is radiant heat coming off the roofing, not that the attic air is hot. I would probably stick to the passive methods of ventilation. |
RE: To attic fan or not to attic fan... that is the questions
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| Continuos run ridgeventing coupled with continous soffit/eave venting with radiant barrier stapled to the underside of the rafters of the trusses or framed rafters, 3" from the eave venting, continuing up to the ridgeventing is a good way to keep your attic cooler in the summer. The heat from the roof is trapped between the roof sheathing and the radiant barrier with the hot air being pushed up and out the ridgeventing by way of the soffit/eave venting. Radiant barrier rolls of 50" x 1000' are relatively inexpensive and is something you can easily d.i.y. Here's a link where we got ours. He leaves his phone # on his website for a reason. I've had many questions concerning our build and the use of radiant for heat retention, and Mr. Ed Sumpolec was extremely helpful. |
Here is a link that might be useful: radiant barrier
RE: To attic fan or not to attic fan... that is the questions
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Dc
Link below to a thread that has been going a long time! Good luck |
Here is a link that might be useful: Whole house fan GW
RE: To attic fan or not to attic fan... that is the questions
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| Thanks for the info all. I had previously read the page about whole house fans, but my electrician was telling us that whole house are different in design from attic fans. The way he described it, the fan we have in the attic is designed to switch on when it gets too hot in the attic and vent the air out, while a whole house is designed to pull more air from the home up and circulate air from the whole home. Is that right? |
RE: To attic fan or not to attic fan... that is the questions
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| Yes, that's right. What the fans have in common is that they run the risk of pulling additional moisture into the house which can be a big problem in a humid climate. The primary purpose of attic venting is to allow moisture to escape rather than to cool the space (a fan will cool the air but not reduce the radiant energy transfer from the roof to the attic floor) so an attic fan can defeat the purpose of venting. If you live in a humid climate and your attic gets hot, install more insulation or a radiant barrier or both. Whole house fans can effectively cool a house in moderate dry climates. |
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