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Confused About Attic Fans versus Whole House......
Old 05-08-2008, 01:27 PM   #1
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Confused About Attic Fans versus Whole House......

I read the threads from two years ago, and I got more confused. Maybe explaining my situation would help.

Last year, as a result of a hail storm that hit our area, I got a "free" roof, siding, gutters, and downspouts. He even threw in the gutter stuff to keep the crap out of it.

I had him put some extra outside insulation (1" foamboard) on a couple area that never had it before (garage and a couple areas on the house. I have a lot of insulation in my attic, and have never had any problems. However, on hot days, the upstairs of the house is about 5 degrees warmer than the downstairs. I am wondering if a solar powered attic fan or two would help.

I don't want to spend thousands of dollars on this project, just vent the attic and get some heat out of there. Any ideas??
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Old 05-08-2008, 02:05 PM   #2
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I read the threads from two years ago, and I got more confused. Maybe explaining my situation would help.

Last year, as a result of a hail storm that hit our area, I got a "free" roof, siding, gutters, and downspouts. He even threw in the gutter stuff to keep the crap out of it.

I had him put some extra outside insulation (1" foamboard) on a couple area that never had it before (garage and a couple areas on the house. I have a lot of insulation in my attic, and have never had any problems. However, on hot days, the upstairs of the house is about 5 degrees warmer than the downstairs. I am wondering if a solar powered attic fan or two would help.

I don't want to spend thousands of dollars on this project, just vent the attic and get some heat out of there. Any ideas??
You would benefit from venting your attic. First it could add a few years to your roof's life. Second it could help keep the second floor a bit cooler. You can either use an attic fan, ridge vents or both. But if your attic is properly insulated already, I don't know whether adding an attic fan will noticeably prevent the second floor from being warmer. The problem might be elsewhere.

In houses with 2 flours the second floor is naturally warmer than the first floor because warm air rises. You can equilibrate the temperature between the 2 floors by (in order of descending costs and descending effectiveness): 1) getting a separate A/C for each floor. or 2) using ventilation inside the house to promote air circulation between the 2 floors. or 3) open the second floor's registers all the way and close the first floor's registers halfway or more: that way more cool air blows where it's warmer and less of it blows where it is cooler.
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Old 05-08-2008, 02:06 PM   #3
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An attic fan simply vents your attach. The blades, whether driven by wind, solar, or electricity, sit almost flush with your roofline to draw to draw hot air out of your attic. With a thermostat, it runs whenever the attic temp gets hot enough. You almost certainly have some ventilation in the eaves, but a fan will help a lot.

I recommend against the wind-powered turbine, because unless you cover it in winter it'll keep venting your attic even if it doesn't need it, and it can blow off in a strong wind (first hand experience). I switched to electrical, but solar sounds reasonable if you don't have a lot of tree overhang. And if you do, your house is may shaded enough you don't really need a fan anyway.

A whole house fan is larger, usually much more powerful, and electical. It sits between the attic and ceiling, and is used to vent your house. The idea is that once the outside air has cooled down in the evening, you open your windows and turn on the fan. The hot air inside your house is sucked up into your attic (and hopefully vented out from there), and cooler air from outside replaces it inside your house. It is just amazing how quickly the air is replaced. But it is loud, so you control it with a switch or pull cord, and usually only run it a few minutes. You need windows open or you'll have pressure problems inside your house.
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Old 05-08-2008, 02:07 PM   #4
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Ceiling fans can also circulate the air inside to help even out the temps. Even in a closed room, the breeze makes it feel a couple degrees cooler.
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Old 05-08-2008, 02:15 PM   #5
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Thanks to all. I have a ceiling fan in the master, which I use. The kid's bedrooms are always a couple degrees cooler, as they sit on the opposite side of the house, while our master faces southwest.

I am thinking an attic fan at each end of the attic might help. My roofer put FOUR vents in instead of the TWO we used to have, but it isn't much better.

How much am I talking to spend for two solar powered attic fans? I would have someone do the work, due to my hobbled nature.........
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Old 05-08-2008, 02:16 PM   #6
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I would add a couple of attic fans to cool down the attic. They really lower the attic temp. The key is to have enough soffit vents to allow the fans to efficiently draw outside air into the attic. I had an issue where a little snow would blow in through the fan, but I guess I could have sealed them in the winter.

Whole house fans are great, but can be noisy. I had one in my last house in the ceiling of the second floor. I would open the basement windows and turn on the whole house fan at night to cool down the whole house. Again you need sufficient attic venting so that the fan isnt restricted in pushing air from the house out through the attic. Also have enough open windows.
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Old 05-08-2008, 02:22 PM   #7
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An attic fan really helped our house (two story), although we needed a second eyebrow vent to provide some additional cross ventilation. In addition to cooling down the attic, it made the upstairs A/C run more efficiently. Without the attic fan, the air coming from the room vents when the A/C would turn on would be downright hot. With the attic fan, the air comes out somewhat warm and quickly cools off.
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Old 05-08-2008, 02:30 PM   #8
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I just picked up a solar gable vent fan - $180 at Lowe's. I plan to install it myself so can't help you there. Not having to wire it is a huge plus.
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Old 05-08-2008, 02:34 PM   #9
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I think these are the best if you can use the house cooling and the attic ventilation. Way quieter than the whole house fans and insulated and does not require extra venting. I bought 3 about 10 years ago for $400 each and installed two in Ca, both horizontal and one in Vegas, vertical because of all the cathedral ceilings and all are running great and even in the summer in Vegas you can take advantage of the cool morning air and run it for a bit and then close off the house and can do without AC until maybe 5 pm. It pulls the air out of your house and pushes it out of the attic.
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Old 05-08-2008, 02:36 PM   #10
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I've done powered and solar attic vents etc and read a lot of in-depth studies.

The solar fans are simply too weak to do anything really useful and the powered fans eat more electricity than they offset in air conditioning. Part of the problem is that most homes are not 100% sealed internally, so when you run a powered attic vent, you get negative pressure in the attic and wall spaces, and this can pull conditioned air from the interior of the home and cause infiltration of unconditioned exterior air...so you suffer a loss on the air you heated/cooled and then have some new air to heat/cool.

Good passive venting gives you some benefit, more insulation is a one time expense and very effective.

I had the same problem with my last two large multistory houses. One way to solve it was to use a wireless thermostat. It has a base unit that replaces your regular thermostat and a portable battery powered part that has the readout and controls. Put that upstairs and the higher temps there will kick off your a/c to rotate the air. It also had a programmable setting to allow the thermo to turn on the furnace fan only for 10-15 minutes once an hour. That pretty much kept the costs of balancing the air down and did a decent job of it.

Another solution is to have an HVAC guy run a secondary sensor from the upstairs to your thermo, but you'll probably need a new thermo that takes 2nd and 3rd sensors.

Whats worked the best for us is using the new hvac system we have installed to run on low continuously. We get about a 1 degree difference between the first and third floor, year round. I think this makes the heat and a/c run a little bit more but the comfort is worth it. Coupled with a high efficiency furnace and air conditioner, the extra work wont cost you much. Most modern hvac systems with a variable speed fan pull about 80-100 watts when running on low...comparable to a large room fan or air cleaner.

Drop in a 5" media or electronic air cleaner and for an extra 20 watts, you have continuously circulated and cleaned air.

We also have a small whole house fan that I installed right into the piece of drywall that drops into the attic opening in the master bedroom closet. When it gets cooler outside than it is inside, I turn on the fan to its low setting (about 1000cfm) and open a few windows in the warmer rooms. Shut it off when we go to bed. The hvac system in the meanwhile keeps circulating the fresh/cool air to all the rooms in the house.

I found that even small "regular" whole house fans pull an awful lot of air on their low settings. They also arent very well insulated and you can get a lot of heat/cooling loss through the louvers. The tamarack one I bought is perfect. It has a low volume low setting and little doors on top with about 4" of insulation on them that get opened by a little motor before operation and close when turned off.

Typical applications of residential ventilation products~by Tamarack Technologies, Inc.

I bought the HV series, made a little frame out of 2x4's for it to drop into, nailed that to the sheetrock drop-in for the attic opening, cut the sheetrock and mounted the grill, and ran the cord to a nearby wall outlet. In under an hour I had a removable whole house vent fan with a remote control. Its a little more work to permanently install it in the ceiling and find a 110v junction to wire it to, but not that much...
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Old 05-08-2008, 02:56 PM   #11
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Cost of a basic attic fan is somewhere around $75, IIRC. I paid another $245 for the installation.
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Old 05-08-2008, 03:57 PM   #12
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Venting the attic requires both input (soffit or fascia vents) and output (gable, ridge, or solar/turbine/electric).
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Old 05-08-2008, 04:47 PM   #13
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A thread at the not-so-friendly hvac site...

Do power attic fans help? - HVAC-Talk: Heating, Air & Refrigeration Discussion

Includes some links to some studies.
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Old 05-08-2008, 08:55 PM   #14
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How confusing...

One guy says attic fans are a "waist" of money, but another says they "seam" to work...
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Old 05-09-2008, 08:21 AM   #15
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Yeah, I meant to make a quip about the spelling abilities of hvac guys, but I forgot.
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Old 05-09-2008, 08:47 AM   #16
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All good information. I added a second solar panel in parallel, and that seems to give the solar attic fan a good boost. You must make sure so have adequate venting though, as noted by OP. Seems to cool the attic a bit but I neglected to measure before and after temps. We swear by the whole house fan though...turn it on in the evening when it is cool and again in the morning to get it really cool...it keeps us cool until late afternoon and helps cut way back on the a/c. We have separate units for the upstairs and the master...areas that are not occupied much, or only at times when the main part of the house is not occupied.
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Old 05-09-2008, 09:11 AM   #17
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I had to add a second panel to mine to get any meaningful spin, and I had to orient the two panels so that they'd get the most direct sun in the 12-6:00 range. It helped but only early on in the day.

The big test I did that I should have done first was using the whole house fan to see if its massive air flow could maintain a cool attic. I measured my attic temps around 128 degrees. Put on the whole house fan for an hour...roughly 8-10x the airflow that the dual solar or a 110v attic fan can produce. Turned it off and waited 20-30 minutes. Attic temp was the same 128.

The $300 I put into the dual panel solar fan would have netted me a ton of blow-in insulation and a free rental from HD for the machine to blow it in with. Another thing to try is the radiant barrier or radiant barrier paints.

I agree completely with the whole house fan. Only thing to watch out for with those is that in some areas the relative humidity at night is extremely high. Pulling in a lot of cool air is good...pulling in a lot of cool very damp air means your air conditioner will have to do a lot of extra work to extract that humidity the next day. Blowing wet cool air into your attic can also produce condensation.

This isnt a problem for me where we live now as the night time humidity is still pretty low. In our old neighborhood we were surrounded with a ton of big farms and orchards, and all of them flooded the fields with 'free' water from their wells at night. The nighttime humidity was ridiculous with all that standing water in the area. If I ran the fan all night, the RH in the house would be 75-80%. Humid air drawn across an air conditioning coil condenses, draws chill out of the coil and refrigerant, and causes the compressor to cycle more. Basically you're paying a higher electric bill to produce cold water that gets dumped on the ground outside your house.

Sooo...lots of room in this venting area for unintended consequences...
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Old 06-13-2008, 12:28 AM   #18
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I read the threads from two years ago, and I got more confused. Maybe explaining my situation would help.

Last year, as a result of a hail storm that hit our area, I got a "free" roof, siding, gutters, and downspouts. He even threw in the gutter stuff to keep the crap out of it.

I had him put some extra outside insulation (1" foamboard) on a couple area that never had it before (garage and a couple areas on the house. I have a lot of insulation in my attic, and have never had any problems. However, on hot days, the upstairs of the house is about 5 degrees warmer than the downstairs. I am wondering if a solar powered attic fan or two would help.

I don't want to spend thousands of dollars on this project, just vent the attic and get some heat out of there. Any ideas??

You just need a solar attic fan with a flow rate in CFM = (attic volume x 10)/60

It wont cost thousands of dollars and it will greatly increase the efficiency of your AC unit(s).


Good Luck!
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Old 06-13-2008, 04:33 AM   #19
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If your really need is to equal first and second floor temperatures, just turn the furnace/AC fan on continuous at the thermostat. Costs nothing to install and can be run only at night if that is when second floor is used mostly, ala bedrooms.... works for me.
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Old 06-13-2008, 07:41 AM   #20
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Venting the attic requires both input (soffit or fascia vents) and output (gable, ridge, or solar/turbine/electric).
I have two attics - put automatic thermostat controlled attic fans on the roof for each.

Turns out motor in the fan for the smaller attic kept burning out - found out two motors later (@ $37 each) there's not enough soffit ventilation in that attic.

The other (bigger attic) fan is fine.

Don't know about the cost/benefit re: electricity costs. Getting a new roof due soon due to hailstorm & planning on ridge vents.
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