no no no to power vents...
didn't we just do this...10 or so pages of no pavs vs pavs?
I think I saved the link :
The cure of the part should not be attempted without the cure of the whole. ~Plato
Nobody mentioned the whirlybird turbine vents, They have sealed bearings in them now days so you dont have to grease them
i personaly like ridge vents they do a great job ,some pavs pull 1.5 to 2.5 amps each
Thanks to the great advice on this forum, Last summer I pulled the plug on my 2 PAV's and the house (especially the upstairs) has been more comfortable, less humid and the AC runs less...
Disconnected another PAV at a customers house today.
One PAV in a 2200 sq ft house with 9' ceilings, 18 clean soffit vents, 14"x6" each.
Despite having a good amount of soffit vents, the PAV was pulling the house into a 6 Pa negative pressure.
Customer said it was cooling better already, 15 minutes after I disconnected the PAV.
Eh, well then i guess its good that I put in the kill switch. I'll just leave it off. Bugs the crap out of me that I kinda have a hole in my roof, but its installed and I'm not screwing around with it. Especially since my attic is not finished at all, no floorboard at all. There is nothign in my attic but blown insulation and my lousy PAV !
Had a fireman years ago talk me out of attic fans. He said they will pull a fire through the house so fast that you could loose everything before they could respond. Just another thought against them.
Its a good Life!
here's a good article on passive attic ventilation. I installed radiant barrier roof decking, and soffit and ridge vents according to the recommendations. With outside temps up to 100, my attic temps never exceed 10 degrees above outside temps. we haven't had temps above 100 since the changes. it will be interesting to see if the 10 degree delta will still hold when they do.
Never thought about the fire angle...another reason in itself not to use PAV's
In many new homes, out of sheer insanity IMO, the gas fired water heater is placed in the attic along with the HVAC equipment. Put a PAV up there...sure, the furnace may not run in the summer when the PAV is in operation, but the water heater certainly does.
Originally Posted by Joe Mascitti
Where will the exhaust gases from the water heater go if the attic air pressure goes negative when the PAV is on? Perhaps into the air exhausted by the PAV? Or perhaps the backdrafting is severe enough to cause flame rollout from the water heater, catching the attic on fire, which is then fanned by the running PAV. Sounds extreme, but possible....
Thanks for all your replies, especially to energy_rater_La for that link (sorry, I forgot to search before posting). A couple more questions have arisen:
I've read that one of the dangers of an overheated attic is damage to composite shingles. It seems a radiant barrier wouldn't help that, and might make it worse. True or false?
Our house has a hip roof in front and 3 gables in back, at different heights. Would ridge vents installed, even on the lower ridges, still be worthwhile as an alternative to PAVs? Existing passive ventilation consists of about 4 square feet each of soffit and gable vents; the total attic area is about 2400 square feet.
I've played around with a few water heaters in attics that have one or more PAVs.
Originally Posted by shophound
On the ones I checked out, the draft hood provided enough of an exit point for the air being pulled down the over fire draft in the water heater wasn't reduced all that much.
Under the right conditions, like in a case of a severe backdraft, I can imagine the velocity of the air coming down the vent pipe being high enough to stop the over fire draft and cause flame rollout though.
One house I found had 3 PAVs, 3 water heaters and 3 furnaces in the attic, with absolutely no soffit ventilation. The water heater vent pipes were backdrafting bigtime, the airflow was actually clearly audible, but the water heaters still had enough over fire draft to work. The 80% furnaces were backdrafting so bad that the draft inducers couldn't close the pressure switches though, lol.
The house itself was being pulled into a 24 Pa negative pressure!
It depends how sensitive those shingles are to a 5 degree increase in temperature. Because it's in that ballpark. Shingle manufacturers I believe used to quibble about that, but now most if not all keep their warranty using radiant barrier. Don't forget these same shingles are recommended for use in very hot places such as Arizona and Nevada. They can stand it.
Originally Posted by astroboy
Hope this helps -- Pstu