Solar powered attic fans? (Northern VA)

[tortillasoup]

attic fans are a bad idea unless they're working at night. They have found that attic fans create a vacuum inside of the attic, sucking out the conditioned air inside of the house. Now if you use the attic fan at night when it's cool, then the attic fan can be beneficial as it will bring in cool air from the outside at night. Just ensure the attic fan shuts off when the outside temps rise past like 80f. A thermostatically controlled attic fan with an internal and external temp probe can work in this regard.

 

[Homerboy]

Our old (broken) attic fan was wired to a thermostat/humidity box. Is that still the preferred method? Everything was wired into the gable of the attic space -- not our actual thermostat in the house.

 

[Mixolydian]

Our old (broken) attic fan was wired to a thermostat/humidity box. Is that still the preferred method? Everything was wired into the gable of the attic space -- not our actual thermostat in the house.

Yes.

 

[Mixolydian]

Attic fans make a HUGE difference, I don't care what anyone says. My parents house has two attics, each with a gable fan. About 5 years ago they both died within a couple years of each other (about 20 years old). Since its a bitch to get into the attics, they were just left there for a couple years before they were replaced. The summers in which the fans were not working were brutal. Noticeably hotter in the house. The A/C would run almost constantly, day and night. So I volunteered to replace them, and the difference was like night and day. Much cooler in the house and the A/C ran about half as much.

 

[imagoon]

attic fans are a bad idea unless they're working at night. They have found that attic fans create a vacuum inside of the attic, sucking out the conditioned air inside of the house. Now if you use the attic fan at night when it's cool, then the attic fan can be beneficial as it will bring in cool air from the outside at night. Just ensure the attic fan shuts off when the outside temps rise past like 80f. A thermostatically controlled attic fan with an internal and external temp probe can work in this regard.

This only happens when they are installed incorrectly without proper venting. Powered fans require additional vents, generally eve vents.

 

[tortillasoup]

This only happens when they are installed incorrectly without proper venting. Powered fans require additional vents, generally eve vents.

I've read of houses that fared worse with attic fans than without attic fans. I'm just saying that now knowing there is a risk of depressurizing the interior and sucking up conditioned air, it should be essential to run the attic fan at night with the cool cold air outside and shut it off when it gets hot during the day. I mean think about it, why pipe in 90F+ outside air when you can pre-cool the attic with 50-70F air during the night, then hope by the end of the day, the attic hasn't heated up past the outside ambient temperatures.


http://www.greenbuildingadvisor.com/blogs/dept/musings/fans-attic-do-they-help-or-do-they-hurt

they're saying don't bother with attic fans at all, I'm saying if you do, try my idea as it may be worth it.

 

[imagoon]

I've read of houses that fared worse with attic fans than without attic fans. I'm just saying that now knowing there is a risk of depressurizing the interior and sucking up conditioned air, it should be essential to run the attic fan at night with the cool cold air outside and shut it off when it gets hot during the day. I mean think about it, why pipe in 90F+ outside air when you can pre-cool the attic with 50-70F air during the night, then hope by the end of the day, the attic hasn't heated up past the outside ambient temperatures.


http://www.greenbuildingadvisor.com/blogs/dept/musings/fans-attic-do-they-help-or-do-they-hurt

they're saying don't bother with attic fans at all, I'm saying if you do, try my idea as it may be worth it.

Your link shows a whole house fans, while talking minimally about an attic ventilation fan. Powered attic fans are sealed in the attic space though what should be a vapor and insulated barrier. The only way for it to depressurize the interior of your house is if there are insufficient vents in the attic (eves or otherwise) to allow for that air flow.

When I was renovating for example, the attic vent fan running did not provide enough pressure to hold up a 8 1/2 x 11 piece of paper to a ~ 5 x 5 hole that went directly in to the attic. The water heater actually reversed the flow and was causing attic air to come in. This actually caused me more concern as it indicated that the outside vents for the furnace room was blocked (with leaves and squirrel activity.)

 

[tortillasoup]

Half the article is about whole house fans and half is about attic fans. Stop skimming and just read the damn article.

Frankly, I don't believe whole house fans work a damn either but that's due to my limited experience with them. One house I was in had a whole house fan, I swear it was less than worthless. I also tried to emulate the results of an attic fan using house fans sealed around windows and having it suck air out of the house through other windows, but with very poor results.

With all of this said, I have had success blowing air directly INTO the house. Instead of using fans to suck in air from one side of the house and exhaust the hot air out of the other side of the house, I just have the fans blow inward. This works significantly better and have been able to cool down the house with great success.

 

[imagoon]

Half the article is about whole house fans and half is about attic fans. Stop skimming and just read the damn article.

Frankly, I don't believe whole house fans work a damn either but that's due to my limited experience with them. One house I was in had a whole house fan, I swear it was less than worthless. I also tried to emulate the results of an attic fan using house fans sealed around windows and having it suck air out of the house through other windows, but with very poor results.

With all of this said, I have had success blowing air directly INTO the house. Instead of using fans to suck in air from one side of the house and exhaust the hot air out of the other side of the house, I just have the fans blow inward. This works significantly better and have been able to cool down the house with great success.

Guess I'll just need to disagree on all of your points. Whole house fan: greatest thing I had at the old house and miss it greatly today. Attic fans: No back draft issues because my attic is properly vented. There is a CO detector 6 feet from the gas furnace and water heater that has a remote trigger to alarm the others in the house, no issues for a decade.

 

[tortillasoup]

How many square feet was the house? Also was the house sprawling or like a two story little thing?

 

[imagoon]

How many square feet was the house? Also was the house sprawling or like a two story little thing?

1235sqft ranch. The vent had multiple speeds and turning it on with the windows cracked pulled air in all over the house.

 

[tortillasoup]

oh, so a tiny house. the houses I tried it with are like 2500+ square feet.

 

[Carson Dyle]

Attic fans are awesome only whenever outdoor air is cooler and drier than indoor air.

Air inside the attic, not the house. And in the summer, it's likely to be hotter in the attic than outside on most days.

 

[Carson Dyle]

With all of this said, I have had success blowing air directly INTO the house. Instead of using fans to suck in air from one side of the house and exhaust the hot air out of the other side of the house, I just have the fans blow inward. This works significantly better and have been able to cool down the house with great success.

Six of one, half dozen of the other. If you exhaust air at a given CFM, it's exactly like sucking air from the outside at the same rate.

 

[bradley]

Air inside the attic, not the house. And in the summer, it's likely to be hotter in the attic than outside on most days.

To further clarify, only pull air from outdoors when the temperature and especially humidity/dewpoint is lower than the *conditioned* space. Only then do I crack open all my lower floor windows and suck out attic air at full blast.

Remember, it takes significantly more energy to remove moist air than dry. Otherwise you are just wasting money better served by installing a reflective barrier... of which my attic has only a 2-4 degree differential from my second floor conditioned space. Without the reflective barrier the differential used to be as much as 30-40 degrees.

 

[tortillasoup]

Six of one, half dozen of the other. If you exhaust air at a given CFM, it's exactly like sucking air from the outside at the same rate.

You would think but in practice, for what ever reason, it was impossible to cool the house down by exhausting the air. I literally waited 12 hours some times to cool the house down and had no success while I did have success when I blew the air into the house coming from the outside. My thinking is that there just wasn't enough velocity and the fans I was using weren't sealed around the blades so they didn't have strong suction power. I was using portable fans/house fans for the purpose of cooling the house...

On the other house that had an actual whole house fan installed, the whole house fan was so completely ineffective, that just opening the sliding glass door completely with no fan blowing had a greater effect on cooling than using the whole house fan with all the windows in the house cracked open which is apparently what you're suppose to do. Relying on convection from the outside air with the windows opened and cross ventilation worked a lot better than the whole house fan. This could have been an implementation issue, a venting issue, a size of the house issue, I don't know, just saying my experience. I have heard good things about whole house fans which is why I was so surprised at it not working all that well.

 

[imagoon]

oh, so a tiny house. the houses I tried it with are like 2500+ square feet.

Heh "tiny." In reality if is the proper CFM it should pull air through the house fine. I guess you could consider the place 2470sqft if you counted the finished basement. The deed didn't so I didn't either.

From your description, you experience was with a whole house fan that was "done wrong." Carsen's comment is accurate:

Six of one, half dozen of the other. If you exhaust air at a given CFM, it's exactly like sucking air from the outside at the same rate.

Fans sitting in windows feel "cooler" due to windchill if you stand in front of it but CFM for CFM they would have the same ambient cooling power

 

[tortillasoup]

Heh "tiny." In reality if is the proper CFM it should pull air through the house fine. I guess you could consider the place 2470sqft if you counted the finished basement. The deed didn't so I didn't either.

From your description, you experience was with a whole house fan that was "done wrong." Carsen's comment is accurate:

Six of one, half dozen of the other. If you exhaust air at a given CFM, it's exactly like sucking air from the outside at the same rate.

Fans sitting in windows feel "cooler" due to windchill if you stand in front of it but CFM for CFM they would have the same ambient cooling power

Well I have a thermostat in the hallway that was not in direct line with any of the windows that were blowing air. I could tell how much the house cooled off based upon the temperature of the thermostat. When I tried sucking air out of the house, it didn't cool that well, but when I blew air into the house by placing the fan outside of the house, and blowing through the screen door, then it worked much better.