Attic Ventilation

[Rtstrider]

Hey guys going to pick your brain on attic ventilation. I have a gable roof with a gable fan. Now there is a huge difference when the fan is running. It is cooling the room above it significantly during the summer, but, is not cooling the rest of the attic. Here is my current gable setup if you are facing the front of the house

Gable vent-------Gable vent w/ fan--------------------------------------------End of the house
(over garage) (about 10-15 feet from the garage opening)

Now my question is would it be ok to add a gable vent at the end of the house with my current setup? Also if I did add the extra vent would I need to seal up the vent above the garage so the fan would be drawing air from the end of the house? Just thinking it may pull from the path of least resistance. Or I have also thought about sealing up what I've currently got and going with a vent on each side of the house so it would be a straight shot across the attic meaning

Gable vent on the side of the house-----------------------------------Gable vent on other side of house

Reason I ask is I can tell a huge difference with the gable fan drawing air from over the garage. I am thinking with the train of thought that it would draw more air through the attic therefor cooling the whole attic (during the summer). I have plenty of insulation so that's not the problem there, it's just that one side of the house is about 10-15 degrees hotter than the rest during the summer and I felt this was the best time of year to tackle this. My main concern is I don't want to put in too much ventillation in there and open a whole new can of worms. What do you guys think?

 

[bepperb]

I would put a temperature controlled fan on the other end of the house and just make sure there is enough intake soffit vents and call it a day. It's hard to over ventilate an attic, but the temperature controlled fan would save energy when it isn't needed.

Or, ridge vent the whole length (or as close as you can to it).

Also, I'm surprised your garage and home attic are open to one another. That would be a massive code violation around here, it really should be a sheetrock firewall with an access panel at the most.

 

[oldhp]

Add the biggest gable vent you can to the end of the house. Block off some of the existing gable vent which will now draw more from the new added vent.
You should have vents on every gable.
The best way is a ridge vent. My roof is a X style, I had gable vents, 4 of them, plus vented soffit's. I had new roof put on and added ridge vents. Huge difference in attic venting.

 

[oldhp]

As bepperb says, garage and house attics should be separate. Against most codes and most important, insurance company's codes.
God forbid you have a fire and they see NO firebreak, maybe NO pay.

 

[Rtstrider]

Well I should elaborate, they did all the footwork to turn the garage into an extra room aside from putting flooring down and putting the water heater (gas) in a vented closet.

bepperb I currently have a temp controlled fan in the attic and like I said it does help just for one room though. That happens to be the same room that has the gable vent (w no fan) above it. So I was thinking if I could just find a way to draw the air through the attic it'd make a significant difference

 

[JTK]

Rts, like said above, I see no mention of soffit ventilation. Without that, you'll never have proper air flow up there to keep it cool. You need to be able to blow air out up high and draw cool, fresh air in from down low.

 

[Rtstrider]

Hey JTK I do have soffit ventilation but I feel that if I were to add a gable vent on the side of the attic that just stays hot, possibly put a fan there as an intake, then exhaust the air out to the existing fan it would cool off the attic better. It would be a temp controlled fan just like the current fan so it would be off when not needed. Would this be a bad idea or would this actually help move air through the attic to keep it cooler during the summer?

 

[Rtstrider]

*wanted to edit my post*

Brain storming....Also would just adding the vent by itself to the other end of house (the extreme end where there is no gable vent) without the fan give the air an outlet to exhaust in decreasing the attic temperature?

 

[JTK]

Originally Posted By: Rtstrider
Hey JTK I do have soffit ventilation but I feel that if I were to add a gable vent on the side of the attic that just stays hot, possibly put a fan there as an intake, then exhaust the air out to the existing fan it would cool off the attic better. It would be a temp controlled fan just like the current fan so it would be off when not needed. Would this be a bad idea or would this actually help move air through the attic to keep it cooler during the summer?


Good deal, you're just about set then. With your setup, you want the gable vents to blow out and draw fresh air up/in from your soffit vents. Install another to blow air out of the attic, not in.

 

[doitmyself]

POWER venting an attic is an entirely different animal compared to passive venting.

It is a very controversial subject and a lot of the old conventional wisdom regarding POWER venting attics is under attack.

Google: electric attic ventilation fan problems...........and study the first 4 or 5 links for some interesting reading.

I came upon this information about 2 years ago when I was addressing some challenging attic ventilation challenges at work.

Read the info and form your own opinion. My opinion is that you can either not do any good with power attic ventilation and/or you "might" make things worse if you don't pay close attention to the details.

Comments?? Even the experts don't agree on this topic. JTK, since you seem to be up on this stuff, I am curious what your opinion is.


EDIT: Here's a start to pique any interest:

Quote:
1. PAVs can create negative pressures in combustion appliances causing the backdrafting
of flue gases such as carbon monoxide in the living space. These same
negative pressures can also draw increased levels of moisture and soil gases, such
as radon, from the crawlspace.
2. PAVs can draw conditioned air out of the house and into the attic, causing the air
conditioning to run more. Conditioned air is then replaced with moisture laden outside
air, creating increased humidity levels inside the living space.
3. PAVs can increase utility costs substantially because of the increased energy
necessary to run the fan and cool/dehumidify the outside air being drawn into the
home.

 

[sleddriver]

1. You need a gable vent on the opposite side.

2. I used powered ventilators for years. Problem is the cheap bushing motors dry out over time, then seize, then blow their thermal fuse and you're back to passive ventilation. So I removed them.

3. I now have a continuous ridge vent and enlarged all of my soffit vents to provide better ventilation. Even in the heat of the Summer inside my attic, two feet above the ceiling, the temp is only 7°F above outdoor ambient. This is also due to light colored shingles AND a radiant barrier.

 

[JTK]

Originally Posted By: doitmyself
POWER venting an attic is an entirely different animal compared to passive venting.


I am by no means an expert on this, but the flow pattern of power vs. passive should be exactly the same, given the system is setup properly.

I've owned and been involved with enough homes over the years to recognize what systems work.

If you don't have a continuous ridge vent, box vents, or gable vents at the highest points and a means to draw fresh air in at your lowest points, power or passive wont work properly. Most homes don't have adequate soffit ventilation, or the ventilation wasn't baffled correctly and is choked with insulation. Some cape cods for instance have no soffits, so all you can do is gable, box or ridge vent.

I also agree with sleddriver in that most power vents won't last but a few years at best. This is why it's important to set it up correctly to let convection do your venting for you.

 

[DBMaster]

I agree with Sleddriver as well. But, with that said, my house came with ridge vents and adequate soffit vents. I added a power ventilator near the peak in 1998 (house was built in 96). I measured the temperature at the floor of the attic before and after (dropped 10°). The air temperature being drawn out by the fan is 140° so the bushings do dry out. The motors last 4-5 years. They are not difficult to replace and cost about $60. An HVAC contractor told me a long time ago that the effective temperature load reduction in the house is about 1-2°. So, for the small amount of power the thing uses I guess I find it worthwhile to keep replacing the motors. YMMV.

 

[doitmyself]

I think the gist of the power vent haters is:

1. Natural/passive ventilation relies on a balanced system of adequate soffit vents and upper vents, with whole length ridge vents being better that gable. Warm air rises and these systems work with no pressure differential.

2. Power vents create a negative pressure or vacuum in the attic. Air will enter the attic to equalize the negative pressure. The problem "can" be that the replacement air might come through the soffit vents (good) or through an unsealed interior building envelope....ceiling, fixtures, wall, chimney/vent cracks etc.

3. The alleged problems with option 2 is that interior conditioned air might be pulled out of the living space (more air conditioning load), could be pulled out of a damp basement, or bathroom, or wherever (humidity problems), or even cause problems with chimney or vent operation (CO poisoning).


I'm not saying I agree about the power vent challenges. However, there are a number of "experts" that claim problems might occur if not properly installed. If the power vent moves 1,000 cubic feet per minute, but the soffit vents can only let in 500 cfm's, then the rest of the air has to come from somewhere.

This is just an academic discussion for me, but the negative air pressure theory seems legitimate. I maintain greenhouses at work and we use both natural and power venting for cooling.

 

[JTK]

Originally Posted By: doitmyself

This is just an academic discussion for me, but the negative air pressure theory seems legitimate. I maintain greenhouses at work and we use both natural and power venting for cooling.


I agree with you. If your fighting an unbalanced system, make-up air has to come from somewhere.

 

[Rtstrider]

Well I'm dead set on using the power fan as it makes a HUGE difference when it is on as far as keeping the house cool. The soffit ventilation is sub par so my theory is I can add gable vents on the last 2 gables and use the current fan setup I have. This will allow the fan enough intake air and in theory wouldn't it draw intake air from the new gables? I can tell you I know it is drawing air in from the gable that is currently near it so in theory wouldn't this allow for more intake air for the fan to exhaust and pull in?

 

[SHOZ]

I use to have those turbine types. They were aluminum and had three of them in a 1500 sq ft ranch house. They worked great for 20 some years. Only had to replace one as it got hit by a flying tree branch and unbalanced it. Still took three or four years before it quit running.


Two years ago I had a new roof put on and had some of the venting that runs down the ridge of the house. It doesn't work near as well as the turbines. Big mistake on my part.

the turbines would even turn with no wind as the convective current going up through them would help drive them. I had two large gale ends vents, three 16" vents per side in the overhangs. And a large 32" sq opening in the garage I left open in the summer.

On a day with wind you could throw up some styrofoam popcorn at the opening and it would suck it right up.

 

[DBMaster]

That does make sense. The instructions that came with the power ventilator - they do come in different fan sizes for varying CFM of airflow - indicated the minimum combined area of soffit ventilation. I had plenty. You also have to watch out, if your house isn't new, for clogged soffit vent screens due to repeated painting.

 

[Rtstrider]

Let me ask this. Would it be feasible to expect the gable fan to use the other gables for intake air then if the soffits are clogged up?

 

[DBMaster]

^I believe so. I installed a gable mounted fan on my dad's house year's ago using that configuration.