power vents and turtle backs

Here's one to ponder. My customer has two power vents installed right below the ridge. These vents are the only sources of roof ventilation. I measured the ridge footage and concluded that we could install about 120 feet of ridge vent, which I think would do a hell of a lot of work than just the two power vents which sit within 10 feet of one another. Customer agrees, then argues that $6 a foot for plastic ridge vent is too expensive. Do you guys agree?

More interesting is his opinion that he should leave the power vents in. Left in and disconnected, according to him, they will function the same as turtle backs (low profiles). He's so convinced of this that he wants to add a THIRD power vent that he has laying around in the attic.. It has no motor.. He just wants to hook it up and "use it as a turtle." I have never read that a power vent not running would operate the same as a low profile.. Does anyone want to put in their two cents? I'd be much obliged.

He's a hardhead and wants to have some say in the job. What he is saying is sort or silly but who cares since it will not matter much. Let him be satisified that he got you to do what HE wanted. Its his house after all right? The attic will still ventilate just fine since the openings for the vents are up near the ridge. Get that job or someone else will. If he wanted power fans that are fully functional mixed with ridge vent i would decline. lol

Fayetteroofing, I hesitate to suggest this because I don't want to insult you-,however- if you have a chance I think it might be helpfull for you to attend an AirFlow seminar if the opportunity presents itself.

Before I go farther- let me just say that in general, I think these types of seminars are 99% designed to simply hype a particular manufacturers product-specifically Airflow and Certainteed- but if you get ONE good idea out of it, it can be big money over the years. The certainteed sales seminars in particular- I got one idea from one seminar-and a second idea from the SAME seminar a couple years later- those two ideas together I am SURE have added$200,000 over the last 15 years AT LEAST.

If you were to go to an Airflow seminar-at the very least- you would have a better idea how to handle this type of customer-and have actual lit. available to show him exactly how his idea is possibly going to cause him problems.

I say POSSIBLY going to cause problems-because maybe doing as he wants-won't cause a problem-9 times out of 10-or 99 times out of 100. in my case- for over 20 years it never caused a problem-untill I had TWO problems in the same year-and right across the street from each other!!!!!

so- now I know better-and have added another item to the list of" things I absolutely won't do"

Ideally, you make sure that the soffit is open so that the air can flow. All the soffit vents in the world won't do any good if the plate is plugged full of insulation. we normally tear out the old soffit and clear out the opening and then install a fully vented aluminum soffit. Once the air can get into the attic, the ridge vent is the way to go. IF you use a power vent with a ridgevent, the power vent will creat a negative pressure beneath the ridgevent and draw air from the ridge and exhaust it out the vent. It may draw some from the soffit, but it is easier for the air to come from the ridge which is nearby.

A power vent with plugged soffit will certainly draw the air from somewhere else...all a bad thing!

Dont get me wrong i have done it and probably will again someday if it means the job or not -- On more than one occaison i have re -installed an electric power fan and they quit working shortly after we do the roof then the homeowner thinks we caused it -- But it has been working fine for 50 years until you did the roof - are you sure you did not break it?

Well in my experience triing to re -use old vents is counter productive -- tearing off cleaning them up -- holes where nailed storing them someplace until driied in then you never know if a seam or a crack or a dent will go bad? then probably have to paint - and they will still look like crap - crew whineing why did'nt he just pay $20.00 for new ones then your competitor sees it when bidding job next door and tells that homeowner -- we dont re -use anything everything is new - that guy probably uses cheap labor anything for a buck --- etc....

"Here in MN the ventilation is most important in the winter months i wish they would make a temp controll that corresponded with the outside air temp -- so if it is 30 out side the fan would run until it is 30 inside the unconditioned space or within a 5-10 degree difference."

I like that idea.

"I agree that the ridge vent and power vent could work together, but I don't feel experienced enough to be judge whether or not the soffit ventilation is adequate on each and every home that I roof.. And therefore I'd rather not take the chance just yet."

That makes sense too.

Oh and Dennis thank you much for your input.. I have also read your posts on roofer.com and you are quite the advocate of the "Short Circuit Myth." My sister is a physics major and she and I have been discussing it, as well. I agree that the ridge vent and power vent could work together, but I don't feel experienced enough to be judge whether or not the soffit ventilation is adequate on each and every home that I roof.. And therefore I'd rather not take the chance just yet.

Wow everyone has such great input. Minnesota: you brought up a good point.. I don't want to be responsible for old vents. But since they won't even be running I assume there isn't too much that could go wrong there.

wywoody Said: In a way, the customer is right, the holes for the power vents will function like a turtle vent-under certain conditions. In a high heat situation with no wind, they probably will exhaust additional hot air. But moving air is lazy, it will take the pathway of least resistance and that probably will be in the turtle vent and out the ridge vent, disrupting the flow from soffit vents to the ridge vents.

So Survivor you're saying that it's probable that the turtle vent will draw in hot air from outside (as in, hot air from the rooftop)? And then the ridge vent will push it out? Not sure I get it. Please explain what you mean.

Yeah, I forgot. We charge between $9 and $10.00 per foot!

$6 a ft ??????????????????

Let someone lose money on this deal

As far as the original post - If the ridge vent has to high of price tag and he wants to keep his power vents as static vents - I WOULD have a problem with it - Only because a vent is a serviceable item that we must take responsibility for and i would prefer they were replaced with new static vents so there is no question as to the condition of the new roof we are installing. Thus rendering the whole performance issue a moot point ( weather a power vent unplugged works as good as or better that a regular turtle vent)

As well as the code is met - and there are no signs / problems with moisture in the attic previously.

Dennis, I can see what you are saying - But by adding the power vent you are rendering the ridge vent as well as gable vents useless - the experiment as well does not show where that inside smoke is coming from and if the soffit vents work properly which i would assume they do - but if they were not to work or were accidentally plugged. then i am sure the least resistance would come from the gable or ridge or conditioned space. (why take the risk?)

Here in MN the ventilation is most important in the winter months i wish they would make a temp controll that corresponded with the outside air temp -- so if it is 30 out side the fan would run until it is 30 inside the unconditioned space or within a 5-10 degree difference.

1.The power vent without power will work better than the slant back. Without wind, just because it is larger. With wind, because air flowing over the large dome will create low pressure and draw air no matter the wind direction.

2. Ridge vents will work with turtle/slant backs. Without wind, the heat/high pressure in the attic will push out of any exhaust hole. With wind, the airflow/low pressure that is acting on the ridge is also acting on the static vent. Drawing air which equals resistance.

3. A power vent will work right next to a ridge vent. Given adequate soffit intake. Within 3 feet of a typical power vent the air velocity is approximately 2mph. And the airflow/draw direction is mostly directly perpendicular to the vent.

http://www.roofingcontractorreview.com/Roofing/Attic-Ventilation/Roof-Ventilation-%7C-Powered-Attic-Fans.html

In a way, the customer is right, the holes for the power vents will function like a turtle vent-under certain conditions. In a high heat situation with no wind, they probably will exhaust additional hot air. But moving air is lazy, it will take the pathway of least resistance and that probably will be in the turtle vent and out the ridge vent, disrupting the flow from soffit vents to the ridge vents.

Stephen is right. Explain to him that air is "lazy" and that it will flow to the point of least resistance. With the power vents running, all that will happen is that since they are nearest the peak vent, the peak vent will become the intake; and that will "short circuit" the "system" and it will not work at all. You cannot mix the different types of ventilation without consequences.

Soffit vents will work with turtle vents and soffit vents will work with power vents and soffit vents will work with a ridge vent, but the ridge and power vents and turtle vents will not work with each other. Something has to give. If he won't change his tune, it should be you saying good bye!