Attic Fan or Not?

[firebroad]

Firebroad,
You could also consider taking this opportunity to invest in some energy upgrades for the attic. The payoff period can be pretty short with air sealing and insulating.
You could seal off the attic and have foam sprayed between the rafters. This really reduces the summer load on AC and heating load too.

The issue is that the A/C unit is in the attic. There is plenty of insulation on the floor--I put it there myself. I believe that the A/C installer put in the fan in the belief that it would keep the unit working better. I am not so sure about the validity of that point, but I will say that I have noticed buckling of the shingles this last year which may or may not have anything to do with the fan's failure.
The roofing company's guarantee is for the next 29 years. They have so far given me no problems with coming out and rectifying any defects that have come up. They would stand to gain nothing from the replacement of the fan, as they would not be the ones doing the work. They may suggest opening the sofits so that the ridge vents work better, but I will know more on Friday. At the moment, I am more interested in getting that hole fixed before we have a downpour!

 

[coaly]

woodgeek, Cathedral ceilings should have fully vented soffit for intake, and ridge vent to pull heated air up each joist space like chimneys. The insulation is held down with styrofoam troughs to allow the air circulation on the bottom side of roof deck. When this is not done, and there is no air flow present, the roof decking stays damp, gets soft and sags between joists. When you can see the outline of ridges where the joists are, that's the problem.
I had a cathedral ceiling section that has headers across 3 joist spaces for the largest roof window andersen makes. 4 foot wide. Before I closed in the soffit (a few years) the bottom of th eplywood decking was getting black under the eve. It's a 2 foot overhang. I hadn't finished the interior wall board, only insulation with vapor barrier. (It took 14 years to build this place from digging the hole to paint which still isn't done) So i bought a 1/2inch Makita angle drill and bored holes through the joists (2 X 10) just under the roof decking. About 2 inches down, I stapled chicken wire across th ejoist space to keep the insulation down from the roof to allow the joist spaces on the sides of the blocked spaces to pull out the top. It has worked so far.
If I had a problem and needed mechanical ventillation, I was going with one of the roof turbin spinner things that do not require electric. That may be something yo ucan use your roof hole for. The new ones are very quiet with good bearings. A neighbor here put two above his breezeway between house and detached garage. It heated up like a greenhouse in there, and those turbin vents did the trick. They seem to be spinning with or without wind. Possibly just the rising air turns them. He puts a bag over them over the winter to hold some heat in his breezeway since it helps heat the house.
There is also such a thing as balance to the vent system. A full ridge vent doesn't pull equally if the intakes are not balanced on each side. Sometimes soffit used is solid with only vented pieces here and there. It should be ALL ventillated. Certainteed makes a soffit panel fully vented that you can't see the holes like a cheese grater. Here's the stuff;


Here's the roof window that is in the entry way with cathedral ceiling that was getting black under the eve BEFORE I even installed the soffit, so it was WIDE open and didn't get any air flow until I ventillated the joist spaces sideways. It made a huge difference. I then covered the insulation and studs with 1/2" foam board and plank ceder T & G. No sweat of the window or stains that are so common with cold glass and roof windows. 6/12 pitch for good draft in joist spaces, 70 feet long. Thought I'd never get done. Well, it's not.

 

[semipro]

The issue is that the A/C unit is in the attic. There is plenty of insulation on the floor--I put it there myself. I believe that the A/C installer put in the fan in the belief that it would keep the unit working better. I am not so sure about the validity of that point, but I will say that I have noticed buckling of the shingles this last year which may or may not have anything to do with the fan's failure.
The roofing company's guarantee is for the next 29 years. They have so far given me no problems with coming out and rectifying any defects that have come up. They would stand to gain nothing from the replacement of the fan, as they would not be the ones doing the work. They may suggest opening the sofits so that the ridge vents work better, but I will know more on Friday. At the moment, I am more interested in getting that hole fixed before we have a downpour!

Having the AC unit in the attice is further reason to bring the attic within your house's insulated envelope.
If you didn't seal all leaks around pipes, ducts, wiring coming into your attic the chances are that the insulation you installed is doing little but filtering the air moving from living space to attic.

Many shingle manufacturers are backing off of requirements for under sheathing ventilation.

Depending on climate and location roof ventilation may not even be needed. "Cold Roofs" are an alternative that is fast catching on.

 

[firebroad]

[quote="semipro, post: 1133197, member: 9487"Many shingle manufacturers are backing off of requirements for under sheathing ventilation.

Depending on climate and location roof ventilation may not even be needed. "Cold Roofs" are an alternative that is fast catching on.[/quote]

Pardon my ignorance, but what does that mean?

 

[semipro]

[quote="semipro, post: 1133197, member: 9487"Many shingle manufacturers are backing off of requirements for under sheathing ventilation.

Depending on climate and location roof ventilation may not even be needed. "Cold Roofs" are an alternative that is fast catching on.

Pardon my ignorance, but what does that mean?[/quote]
This is a good reference from the folks at Building Science Corp. It was published in Fine Homebuilding. It covers both ventilated and non-ventilated (cold) roofs.
http://www.finehomebuilding.com/how-to/articles/a-crash-course-in-roof-venting.aspx

 

[mellow]

I am in the same boat, I have our upstairs air handler in the attic. I have soffits and a ridge vent but I also have a window on one end, during the really hot days I plug in a window fan and let it run blowing air towards the ridge, my thought is it will help draw air up and out. I have tried blowing the air out the window but that interferes with the ridge vent.

My main concern is keeping that air handler from roasting.

 

[firebroad]

I am in the same boat, I have our upstairs air handler in the attic. I have soffits and a ridge vent but I also have a window on one end, during the really hot days I plug in a window fan and let it run blowing air towards the ridge, my thought is it will help draw air up and out. I have tried blowing the air out the window but that interferes with the ridge vent.

My main concern is keeping that air handler from roasting.

I have a suspicion I will just have to get another 5 year roof fan up there, else spend a sh**load of money. Oh well.

 

[woodgeek]

OK, I get and agree with ventilating the attic for moisture removal (cathedral or otherwise), but think a properly airsealed and insulated conventional attic floor will make an attic fan a moot point re heat load to the house underneath. I also figure the sheathing is R-1.5 under the shingles and less than R-0.3 from the shingles to the atmosphere, so the shingle temp won't care much either about the attic temp. Making the attic 10 degrees cooler might drop the shingle temp 2 degrees.

My air handler is also in the attic, and if the OP is getting a lot of AC load when the attic is hot, she should look over the return ducting...I had 3-4 sq in of gaps in my return plenum, which under 100 Pa suction from the handler let in a bundle of air. Supply side leaks are bad too, but not so bad in a hot attic as pulling that air in.

 

[woodgeek]

I have a suspicion I will just have to get another 5 year roof fan up there, else spend a sh**load of money. Oh well.

The only moving part is the blower motor, and it is in a conditioned airflow (i.e. cool) when it is running. Whenever it is hot in the attic, your AC will be cycling...how hot will the motor get during an off cycle...the housing is usually rated to R-5 or better....and it a motor! they are built to run hot. I have never worried about my handler getting too hot... The controller boards are electronics, and 60-70°C is no bigs.

What am I missing?

I HAVE worried about my condensate pump freezing in the winter, cracking, and leaking in the spring.