Roof: Ridge Vents AND turbines?

[Todd Burch]

My thinking is "the more, the merrier", as far at attic ventilation and air exchange opportunities go.

I have a ridge vent now, and will be getting a new roof as soon as it stops raining. (hooray for the rain!). I told my roofer I wanted to add turbines and keep the ridge vents. He said no problem.

For piece of mind (on the pricing I got) I had another roofer come give me a bid this afternoon. Price was right in line with the other, but we had an argument over using turbines AND ridge vents.

He said to use one or the other, not both. He said if I used both, there would be "stagnant air" above the turbines (inside the attic at the ridge). I asked what stagnant air was. He said air that would not move. (I'm laughing to myself at this point). I asked why it wouldn't move. He said the "cold air pushing up into the soffit vents would all be going out the turbines". I told him "cold air will never be pushing anything up, and that hot air rose, and created a low pressure that sucked 'cold' air up through the soffit vents". He didn't seem to grasp this.

I then asked "why wouldn't hot air, above the turbines, and below the ridge vent, not also be rising and going out the ridge, either through normal processes, or even from being drafted out. He then looped back to "Use one of the other - you'll create stagnant air". We did this twice, and then he finally said "hey, if you want both, I'll do both."

I thanked him for his time and his bid and showed him the door.

Am I nuts?

[Dan Hintz]

It's not often you find a contractor-type that understands beyond his rules of thumb... they exist, but they're a rare bird. If he doesn't even understand the concept of hot air rises, it's best to let sleeping dogs lie...

[Jim O'Dell]

I had understood that you don't use both. Ridge vents are better as they are at the highest point of the roof so all of the heat escapes. I don't know if there is a reason not to have both...maybe look on the websites for the ridge vent manufacturers and email them for the proper answer. Jim.

[Jim Matthews]

I'm sure he had a few choice words about your acumen, safely back in the cab of his truck. Few particle physicists change careers to work in construction.
Berating someone with a limited grasp of physical principles (even in their field) comes off as smug. I know, I'm blacklisted with the local framers over a similar exchange.

Fewer perforations are better. I'm with you about the ridge vent, solo. If you're interested in overcoming the stack effect, you'll need an impeller to draw air through the house.

I have tried a large Fantech in line duct fan to accomplish the exchange you describe - it's all about CFM and overpressure in the attic. There's a good deal of resistance through soffits and ridge vents.

[Joe Pelonio]

The way I understood it is that the turbines pull the air too fast so the flow is simply bringing outside air in through the ridge vents and back out, rather than exhausting the attic air. Soffit vents with either ridge or turbine are supposed to be the way to do it.

[Joe Angrisani]

If the "sucking" effect of the turbine inbound through the ridge vents were equal to the "hot air rising" effect of convection, wouldn't things tend to stagnate between the ridge vent and turbines? The turbine is drawing in from both the soffits and the ridge vent.

There's no doubt the turbines are stealing at least some of the ridge vent's efficiency.

EDIT: Or as Joe wrote while I was writing: The turbines make the area below the turbine stagnant, thereby heating the ceiling of the living space. Poor Mr Stagnant might have been right. :p

[Brian Effinger]

My thinking is "the more, the merrier", as far at attic ventilation and air exchange opportunities go.



That is not necessarily true.

While a vented attic is a good thing, what you should also be trying to do is pressurize the space. There should be more air coming in your soffit vents than escaping through the ridge. If the attic isn't pressurized, then you could be sucking up the conditioned air that is in your house, and into the attic, where it can cause all kinds of problems. I have seen several instances, just in the past year, where there is too much air moving though the attic, and it creates a stack-effect, drawing moist and conditioned air up into the cold attic in the winter. The warmer, moist air will then condense and freeze on the underside of the roof deck, and when it melts in the spring, mold grows. These were mostly older houses had been recently re-roofed. The contractors would not install a roof without adding soffit and ridge vents because the shingle manufacturers wouldn't warrentee the product without them. Unfortunately these older homes aren't sealed very well, which creates all of these problems.

There is a wealth of info out there about these issues. One name to google is Joe Lstiburek. He is a PhD and is one of the smartest people in building sciences.

BTW, I'm sorry if there are spelling errors in the above post. My spell check doesn't seem to be working right, and I'm horrible at spelling.

[Jason Roehl]

I don't think both would be a problem. Even if the turbines were drawing air through the ridge vent, they'd be drawing in 95-100ºF Texas air (I seem to recall Todd was in TX, anyway). On a sunny day, even if it's that hot, the attic would be pushing 150ºF or so. That temperature difference would set up a pretty strong convection that would certainly mix with the airflow between the ridge vent and the turbine and make its way out.

I guess if you do both, you'll just have to go up there with a piece of paper or something to see if air is going out the ridge vent or getting pulled in.

I have both ridge vent and a powered gable fan in my attic. I think the fan helps (was not operational when I moved in, so I replaced it after a while).

[ray hampton]

do you locate the vents and turbines so that they are facing toward the wind or facing away from the wind ?

[Van Huskey]

Right for reasons he doesn't understand, better than being wrong but have a logical explanation of why one is right.

Don't mix outlet vents on a roof. The stringer vent tends to turn the weaker outlet vent into an inlet vent and your flow tends to be primarily between these vents. The air needs to flow along the underside of the sheathing not between two vents. Do the numbers find the total NFA needed and choose type of outlet vent to accomplish this, that is the best solution, ridge vents are usually the way to go if your total roofline is long enough to support the needed NFA. Also note there is a wide variation in the NFA per linear foot with regard to ridge vents, so if one product isn't good enough there well may be better.

[Todd Burch]

I was reading somewhere that the air exchange calculations were based on square feet of attic space. I found that surprising, as I expected the calculations would be on volume of attic space, not attic floor square footage.

I'm still researching...

[Todd Burch]

I just read that the 2 gable vents on the front of my house are screwing up the operation of my current ridge vents. Oh, brother.

I think I may lose the ridge vents, go with the turbines, and close up the gable vents.

[Todd Burch]

The ridge vent companies hate the turbines.
The turbine companies hate the ridge vents.
I found one site that hates them both - obviously because they have their own solution.

This is crazy.

No facts, but a heck of a lot of opinions.

I suspect one might be more appropriate than the other for a given attic configuration, and blanketing one application for all is probably overstating and inappropriate.

Perhaps I'll put my roofer to the test, and let him tell me, based on my attic square footage, attic volume, exposure, and current soffit NFA capacity, what type of exhaust venting capacity I require.

People talk about turbines drawing from ridge vents. Couldn't one turbine also draw from another turbine? Or a higher ridge draw from a lower ridge?

[Brian Elfert]

In the perfect world a house shouldn't be leaking conditioned air into the attic. Many houses do leak air into the attic because builders didn't care so much about sealing things up when energy was still fairly cheap. A lot of today's new houses are much better sealed. The state of Minnesota energy codes require all kinds of sealing of houses to minimize air leakage. Houses also have to have air exchangers to bring in fresh air since there is little leakage to being in fresh air.

[David Weaver]

If the ridge vent is close to the turbine, why wouldn't you end up with both vents just feeding the turbine?

There's no reason to have both, and aside from it being a waste of money, i've seen people mention condensation issues before when the cold vs. hot air mix is not even.

I only have soffit and gable vents on my roof. I'm sort of dreading the day that I get the ridge vents installed, because thus far, it's warmer under the roof in the winter, and the paper wasps can't tolerate the heat in the attic in the summer. If it cools off some, I'll have paper wasps in the attic sooner or later.

[Larry Edgerton]

I have no opinion on this matter, but it is comical.....;)

Larry

[Ryan Mooney]

I have no opinion on this matter, but it is comical.....;)

Larry

Said it before and I'll say it again that the one thing I know for sure about fluid dynamics is that I don't understand fluid dynamics. I'd bet that 99% of the people who install these sorts of things have no idea how why certain things are done the way they are, but just that they know they work because they've worked the last 10,000 times and if you screw with the formula bad things happen (and no problem with that, if we all had to understand everything we did from first principals we'd never get anything done - "mom why does water expand when it freezes?" lol).

Working on computer room cooling I've seen some really weird things (like the computers closest to the chiller are often the hottest because the airflow is so high it just shoots right past them, The computer above a baffle that stuck out 2" was ~30F hotter than any of the others in the rack, etc..). I would reckon that any of the above speculation is possible, actually knowing for sure is more complicated than I'm willing to try to calculate anytime soon :p My few forays into things involving air movement have been pretty universally "educational" if not always productive... :rolleyes:

[Pat Barry]

How would you locate a turbine vent so it wasn't facing the wind?

[Van Huskey]

Said it before and I'll say it again that the one thing I know for sure about fluid dynamics is that I don't understand fluid dynamics.

We have a friend that is one of the worlds foremost fluid dynamics guys (he is a F1 car aerodynamicist). I am a huge fan and on the rare occasion we are in the same room (he is in the UK) I usually make him talk shop. When I ask about a teams new design and why they would do that I understand about three words of his next 2 thousand, all three of which are conjunctions. Two of our mutual friends feel the same way and they are both engineers.