Thread: Attic ventilation

I stumbled across this today while looking for something else and found it quite interesting: http://www.dom.com/about/conservatio...entilation.pdf

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As an Energy Auditor I'm familiar with this and what's written is true. The attic fan is installed with out enough area for make up air. The attic is so connected to the house that is pulls air from the interior. This includes conditioned air and moist air. When there isn't proper air sealing the fan can just make things worse.

Because of the stack effect that this creates wouldn't it also increase the level of Radon entering the structure?

Those wind driven turbine vents can do the same thing.

Originally Posted by Tom Rees

Because of the stack effect that this creates wouldn't it also increase the level of Radon entering the structure?

If there was radon that could always be a possibility. There has been evidence that the more stack effect the higher the radon. The idea is that air and moisture are actually able to be sucked out of the dirt.

I found the article to be very poor.

It starts out with a position against attic ventilation in general but its only real point was against power ventilation. And then most of the argument presented assumed leaky penetration points. (Which of course often exist, but shouldn’t.) Thus the whole ‘don’t vent the attic’ position actually sidestepped the true issue of ‘don’t have air leaks.’

Indeed the last page (#5) promoting passive venting contradicts the first page where the writer states “… research to the contrary.”

A classic case of not looking at a house as a whole system of integrated components.

I would agree with the 'not a good idea' premise if the attic fan was of the automatic temp control type.

Having a manual control with timer is a useful application.
Examples could be; A/C not normally used and the vent is used to evacuate air from home and attic with windows open of course (speaking of a whole house fan obviously), or, owner comes home from work and temporarily turns on attic vent to evacuate the incredible heat that has stored up thar
during the day.
Here is my favorite and used by yours truly; Contractor and/or Inspector needs to go up in the 140 degree attic... only takes a couple minutes while your doing something else, to cool down the attic to human tolerance.

Originally Posted by bob smit

Here is my favorite and used by yours truly; Contractor and/or Inspector needs to go up in the 140 degree attic... only takes a couple minutes while your doing something else, to cool down the attic to human tolerance.

Nah ... just cut a hole in a ductboard distribution box when you are up there, then tape the piece back in place ... Oh, wait, dang it! Forgot to bring the duct tape into the attic, what do I do now? Ahhh ... write up in report that a cut out hole was found in a ductboard distribution box and an a/c contractor needs to seal it in place as it may be leaking air from the attic into the house.

I thought the article was fine except for the part where it mentions that attic ventalation does not have a big affect on attic temperatures. Whoever wrote that has never been in a Texas attic in the summer. My experience is that a properly ventilated attic does significantly lower the attic temperature. Other than that, the article was "okay". Appears to be written as promotional material for some product. Typical stuff.

cant wait to try that whole idea out J.P. lol

Whenever I run across powered attic fans (either through the roof or at a gable vent), I always recommend removing them for the reasons mentioned in the article.. namely, possible back draft of fossil fuel appliances, wasted energy from running the A/C, etc. plus this can also void shingle warranties. The ASHI Reporter had a very good article in it a few months ago on this topic. Check it out!

Interesting sidebar. Here is GA, as of 1-2011, the GA Energy Code no longer allows the installation of house powered PAV. If a PAV is installed, it can be solar but not connected to the home's grid. Apparently, PAVs are most certainly falling out of favor and it makes perfect sense. I never recommend them. If I see one that is NF, I recommened another form of ventilation.

He made some valid points but it was not well written. If you note current energy efficiency starts with sealing the attic floor. So it should come as no surprise that any negative pressure in the attic will cause air to leak out of the house. A power vent will make it worse.

Radiant heat from the roof has a bigger effect on the house temp than does the attic air temp. Attic vents have a small efffect in keeping the temps down and but doesnt affect the radiant heat factor.

Proper attic venting includes baffles the full width of each and every rafter bay. This allows the air to flow where its needed. How many times have you seen it done this way? How many times have you seen mold down low on the roof away from baffles?

With good air sealing and insulation an attic does not need much venting, that is a passive 1/300 ratio works well. There would be few mold or ice damming problems. Use cellulose as it is better at blocking radiant heat.

Powered as ion plug in is rather silly as you use energy to save energy as far as the attic cooling goes.

The part about ridge and soffit vents or gable and soffit vents is alright but as far as just vents at the ends of the attic I just never agreed with as the slow moving hot dead air in the middle of summer heats that attic up substantially. A well sealed home with ridge and soffit vents is the way to go or if you have one of those roofs with small to very small amount of ridge then a solar fan and soffit with a well sealed home is the best bet.

Another point would be low pitched roofs and ridge vents. I just don't think they are the best idea. The taller attics with greater roof pitches seems to be the best bet with ridge vents. Lower pitched I would go with the solar vents and soffit vents.

As far as leakege through lights etc Seal them up and properly vent the attic. With all those leaks nothing will be optimal. That would be the no brainer