Whole house fan install tip?

[Fuddy1952]

Neighbor gave me a 36" whole house fan. He barely used it, his wife prefers ac!
It runs great, but I could see where the blades have been installed on the miter shaft in different positions. Where is the best air flow, blades in the venturi housing?
In the new barn I'll put it in the cupola since it has vents it would be great pulling air up and out cupola. As you see it will go between two rafters, I won't cut any purlins as that won't affect air flow much, of course I'll have to cut/remove insulation there.
My idea is make a box, 2 sides rectangle, 2 sides triangle to match roof pitch. I'll have it on switch, probably a thermostat.
Thanks any ideas. It's high up so hoping to make it easy!

 

[Fuddy1952]

Spellchecker. Miter shaft supposed to be motor shaft

 

[JerryK]

I think the best blade position for a fan is with them rotating close to the circular opening, which you may be calling the venturi position. Box fans that have this circular metal piece seem to pull/push air better than a cheaper one that is just square. I think you will really like how much hot air it pulls out of you under roof area.

 

[TnAndy]

We have a 48", two speed one mounted in an upstairs closet wall that vents out to the attic. That is our main 'air conditioner' Flip it on at night when the temps dip into the upper 60's or lower, and it will suck the bedroom curtains out to 30 degrees, and have you reaching for a blanket in the middle of the night. Love it !

 

[Fuddy1952]

I made a simple drawing looking at fan from edge. The blades can be moved forward away from motor or back. Right now it's halfway, like #2 sketch. Would it move more air like 1,2,3? Thanks.

 

[Fuddy1952]

Sorry...right now half way like #1.

 

[LS Tractor Owner]

Ours is like #1, ours works great! Like TnAndy said, we need to reach for a blanket.... It really won't matter in your situation / usage where the blades are positioned. What will matter is that the "exhausted air" actually gets exhausted through the cupola. Make sure the sides of the 'triangle' are closed off, also on the 'rectangle' sides up between the rafters and purlins. Basically a "shaft" for the air to go up into the cupola then outside. You will definitely notice a difference!

 

[MossRoad]

Neighbor gave me a 36" whole house fan. He barely used it, his wife prefers ac!
It runs great, but I could see where the blades have been installed on the miter shaft in different positions. Where is the best air flow, blades in the venturi housing?
In the new barn I'll put it in the cupola since it has vents it would be great pulling air up and out cupola. As you see it will go between two rafters, I won't cut any purlins as that won't affect air flow much, of course I'll have to cut/remove insulation there.
My idea is make a box, 2 sides rectangle, 2 sides triangle to match roof pitch. I'll have it on switch, probably a thermostat.
Thanks any ideas. It's high up so hoping to make it easy!View attachment 607382View attachment 607383View attachment 607384View attachment 607385View attachment 607386

Ours is set up like yours is right now, with the blades centered halfway in and halfway out like your picture.

 

[fitter1]

You may overload motor depending on this position of fan on shaft. Use an amprobe when setting this up.

 

[jfh28]

one of the things you are going to want to check is the net free air space of the cupola......in other words the sq inches of space that is not blocked and will allow the air to exit......if its wire meshed then you will need to look up the reduction factor for that number......match the net free air space against the required exhaust rating of the fan......it should be equal or larger......if its not there will be a backup pressure of air flow as more air will be entering the cupola then can exit......I've seen many fan motors prematurely burn out due to this situation......Jack

 

[EddieWalker]

Back in the olden days attic fans where very popular here to move the air around enough to help keep the house a little cooler. They did work to a certain degree, and I know some people that liked them. Not enough to not get air conditioning. In the last 15 years or so, I've removed or sealed up about a dozen of them for clients. All where in perfect working condition, they just never use them and they hated looking at them, and knowing that they where huge holes in their attic insulation.

I can't imagine anybody wanting to put one into their house when AC is so effective and energy efficient compared to an attic fan.

 

[Fuddy1952]

Shade trees for house and garage is amazing. We have central air for house, rarely ever use it.
Garage people think it's air conditioned but it's not. It has a cupola also above second floor.
The contractor was out yesterday, we looked up fan cfm and perfect match for that same cupola.
Now I'm waiting for negative replies about trees!
House averages low 70s in summer, low 60s in winter.

 

[Lineman North Florida]

Shade trees for house and garage is amazing. We have central air for house, rarely ever use it.
Garage people think it's air conditioned but it's not. It has a cupola also above second floor.
The contractor was out yesterday, we looked up fan cfm and perfect match for that same cupola.
Now I'm waiting for negative replies about trees!
House averages low 70s in summer, low 60s in winter.

That's good if it works where you live and shade trees do help but down here in Florida they are no match for air conditioning, actually if not for A/C we would probably be a densely populated state, probably not many wanting to move down here.

 

[Industrial Toys]

I tried replacing the centrally located attic hatch with a couple of those fans designed to go in a window, thinking it would draw hot air upward out of the house, into the attic, suck cooler air in the open windows, after sunset and ultimately expel hot air through the attic vents. It did not work at all.

 

[/pine]

In the days when attic fans were popular most homes did not have insulation (especially in the walls)... many had loose, double hung sash windows...window shakers were the norm for AC and they were not efficient at all...
...A major factor with modern AC systems being very efficient lays heavily on how well homes are insulated including thermal windows (multiple panes)...

The key to using attic fans was judiciously opening windows in rooms that were occupied and keeping others closed to have the max amount of air flow where it was needed...

 

[Industrial Toys]

So, it's not the efficiency of the AC but the modern insulation practices. An architect told me that central air is not very efficient and he tries to use those split units as much as possible, where they needed the most.

 

[California]

Sounds like they are only suitable for some climates.

At our home in town, in California's Central Valley, the whole house fan is ideal. Low humidity, and normal summer highs are 85~100 with a few days 104 up to the hottest I've worked in, 114. As soon as outside air falls below indoor temperature, turn it on and open many windows. Run it till maybe 7am so long as its still cooler outside, then seal up the house.

This cools the interior structure, furnishings, etc so then the house stays cool all day. This plus an oak shade tree that keeps the sun off the roof until late afternoon (and modern spec insulation) are sufficient. The A/C is run only a few days per year when it stayed hot overnight.

There has to be a substantial cost savings running this vs A/C. Also the entire interior chilled and quiet vs the noisy and drafty A/C is more pleasant.

This won't work for everyone but its ideal for this climate. If you don't have lows below 70 overnight it wouldn't be useful.

 

[MossRoad]

Sounds like they are only suitable for some climates.

At our home in town, in California's Central Valley, the whole house fan is ideal. Low humidity, and normal summer highs are 85~100 with a few days 104 up to the hottest I've worked in, 114. As soon as outside air falls below indoor temperature, turn it on and open many windows. Run it till maybe 7am so long as its still cooler outside, then seal up the house.

This cools the interior structure, furnishings, etc so then the house stays cool all day. This plus an oak shade tree that keeps the sun off the roof until late afternoon (and modern spec insulation) are sufficient. The A/C is run only a few days per year when it stayed hot overnight.

There has to be a substantial cost savings running this vs A/C. Also the entire interior chilled and quiet vs the noisy and drafty A/C is more pleasant.

This won't work for everyone but its ideal for this climate. If you don't have lows below 70 overnight it wouldn't be useful.

Humidity is the biggest problem here. In summer we average mid 70% and by morning, it's almost 90% humidity. It can get pretty uncomfortable at 78 degrees outside with 85% humidity.

 

[jfh28]

the main difference between a fan and a/c is that a/c removes moisture from the air thus lowering the humidity and increasing the comfort level inside the building......which is why it's critical to properly design the size of an a/c system.....if its to big it will cycle on and off to quickly to remove enough moisture....to small and it won't be able to handle the load......with the whole house fan system you will be drawing the uncomfortable air out of the house but you will be replacing it with outside air......so if its hot and humid outside that's the air you're bringing back inside...the movement of air across your body won't do much if it's hot humid air......if its cool and low humidity outside then that's what you will be replacing the inside air with and it will feel much nicer.......so a whole house fan system is very location dependent......I have found in my area it works best using it in the early evening hours once the temps drop down......whereas an a/c system will work any time......but at a higher running cost since you will be powering both a circulating fan and a compressor.......which is best for you will be highly dependent on location and environment.......I have a/c but probably only run it for a total of one week out of the whole year....but without a doubt it's worth it to have for those few times......Jack

 

[/pine]

There is really no debate between an attic fan and a central AC system as far as maintaining a comfort level in an entire house...

Not sure if the trend is still on for large rooms with high ceilings but many were built in the last decade and that increases the demand on an AC system...

With a central system if it is on you are constantly moving all the air in the entire home...whereas with an attic fan you have the option of only moving the air in the rooms you wish...