Power ventalator vs turtle vents
 

I am having a new roof installed on my house and the roofer was going to get ride of all the turtle vents. Then install 1 power ventaltion fan with a thermostat. I live in the south in case this makes a differance. My house is approx 20 yrs old and I am havin 30 year shingles installed. Does this sound correct to all you roofers out there? Thank you

I would look into a Ridge Vent System.Requires no electric,Does the work of Multiple vent.Plus heat rises to the ridge,so there is always going to be heat excaping the attic.A power vent on the other hand has to pull hot air from the entire roof which can lead to constint running of the vent causing the motor to burn out.Leading to the replacement of the vent.

I'd avoid the power vent in most situations. As noted above, they require power to do what can usually be done without it. Also, if the proper inlet is not provided, the power vent can draw conditioned air from the living space.

This is an often discussed subject. Do a search and you'll get a lot of opinions.:wink:

You probably saw these in your research: http://www.advancedenergy.org/buildi...%20Studies.pdf

http://www.ronhungarter.com/black_mold.html

http://www.ronhungarter.com/ventilation_repairs.html



http://books.google.com/books?id=Eq1...page&q&f=false


Be safe, Gary

One good thing about a power vent vs. relying on the ridge vent is that the power vent pulls air quickly...faster than natural convection.

With the power vent, you pull air from the soffits and some air into the ridge vent, but again, more air is being exhausted faster.

A ridge vent also relies on external wind power to draw the hot air out to be effective.

Also, with the power vent, have the electrician install an accessible on/off switch, so you can override the thermostat and turn it on when it gets hot outside.

If you look at pictures showing the ideal flow of intake and outake air, it from a static perspective. It doesn't factor in that as the temperature rises, so does the pressure increases (ideal gas law) in your attic.

Therefore, all those vents that you have in the roof will probably be outlets for the hot air vice intake, unless your outake is much greater than your intake.

Power vent vs Ridge vent
 

Don't do it, go with the suggested ridge vent, make certain they cut out the plywood correctly at the ridge and set the ridge vent in mastic, use Zac 2" screws instead of nails and butyl calc ridge vent joints. Make certain you have soffit vents or vented screen on your soffit (overhang) to allow cool air in (the chimney effect). Make certain they follow NRCA and local code guidelines and have the roof inspected during installation.

One power vent will not do the job, it is impossible. If the power vent fails you’re left with no venting. Hot air rises as cooler air enters through the soffit vents, they work by the natural laws of physics without the use of electric.

Once the new Carbon Credit tax goes into effect along with the new Zero energy building requirements take affect (reduction of energy consumption by 60%) your electric bills will raise by 408%, from $.12 to $.49 per Kilowatt Hour, you will wish you did not have those power vents.

Regards

FYI, if he OP goes with a solar attic fan, then there is no electricity cost.

I agree that a ridge vent needs to be cut, but an attic fan moves hot air faster.

I haven't spoken to a single person who had an attic fan installed that said they felt no difference since the fan was installed.

As I mentioned he will need several electrict fans. A atic venting calculation will have to be done in order to properly desing the correct amount of venting required and if he disides to go with power vents he will find the correct quantities needed, it may be costly.

That really depends on the size of the house.

A fan operating at 1400 CFM can handle an attic 2000 sq. ft.

calculation => 2000 x. .7 = 1400 CFM required

For 10 ACH this is about right for a 3' high gable roof 16' wide.

For whatever reason, calcs to determine required CFM only factor in length x width, not height.

Yes, so then they assume and do not mention an avg. height and/or some number of Air Changes per Hour. It's probably because calculating the volume of an attic for a hip roof or other geometries can be tedious, but doing it can save you utility bill money.

CFM is a volume measurement and sq. ft is an area measurement
so somewhere there is a conversion being made.

The ACH is one major determinant of attic temperature. Once you know this basic quantity you can make your own calcs about the desirable CFM and temp. drop, rather than taking the manuf's word for it.
I know of one case where the manuf. recommended 22 ACH. That's easy if they are not paying for the fan kwh.

And some of these solar fans have an unbelievably high number of CFM for the watts inputted. Caveat emptor.

Yes, I'm aware that "cubic ft" is a volume measurement and "sq. ft." is an area measurement.

I wouldn't say it's tedious to calculate. Estimates can be made and the formula is already coded into the website.

I guess what's lost in the "not paying for the fan kwh" is the "benefit" derived from a cooler attic that could translate to longer roof/shingle life, cooler upstairs, etc.

I'm wondering what the point of diminishing returns is. How many ACH is no longer of noticeable benefit? Somewhere above 10, I guess.

Also, people move every 7 years on average.
For shingles that last 30 years on average how much in yearly utility bills should the present HO pay to cool the roof and forestall roof failure? And how exactly is a roof failure defined?
When a water heater fails, this point is known within minutes or hours.

The comfort factor is another issue. Would the money be better spent on a larger central AC or upstairs window units?

No, this does not make any sense at all.

Besides going with a ridge vent system with properly sized sofit vents, as well as vent chutes to keep that air flow clear, you roofer should have talked to you about getting a 15% tax credit back from the government for your new shingles.

If you chose to get the GAF White energy star approved shingles, you would get back 15% of the cost of those shingles... plus they would reduce the heat gain on your attic. Around here, the difference between 25 year asphalt shingles and lifetime white architectural shingles? $18 a bundle for 25, $21 for lifetime... and you get that $3 per bundle returned to you on your next tax return. Sweet.

Have to buy the materials in 2010 to qualify.