etc    i know in my current house, 1-1/2 story home, the knee walls in the second story were insulated but the interior temp of the wall would still be hot enough in the summer months that leaving your hand on it for more than 5s was uncomfortable. Anyone have a good product suggestion for accomplishing that? Knowledge is power! A large study showed that factory applied RB (~10 cents/ft2 extra) is only marginally cost effective in homes built to 2006 energy code. Another way to look at it is to compare static exhaust vents to a continuous ridge vent. To better understand attic ventilation, it is best to start with the basics. So far my results are fairly exciting. Regarding this point, Danny Parker wrote in a literature review of attic ventilation, "Detailed simulations suggest that the heat transfer in an attic to a residential building interior in mid-summer is dominated by radiative gains from the hot roof decking directly to the insulation surface. My house is like a cape without the dormers. I don't even know what to search for on Google. So if you measure from the outside and it's 1" from the bottom of one louver to the top of the one below it, and the space is 10" wide, that's 10 square inches. Hey "Lady", er, Allison ? Please help me to understand, that although the attic fan is on, there is no insulation in the attic, the attic isn't sealed, why is the smoke puff test not reliable in this situation? This house was a Spec and apparently the builder didn't consider positioning when deciding on the house design and types and size of windows...... Another thought I had was to put some kind of film or coating on our West windows to help limit the amount of sun that penetrates. For the rest of the house we use individual ceiling fans and keep many windows open. For me the equivalent area would be 4 hatches about 15 ft. long by 20 ft. high. Recommended for kitchen duct outlets, bathroom fan exhausts, as well as attic ventilation. the RB bays produced the same floor interior temp as the R19. Learn how your comment data is processed. With the attic fan on, I tested the outlets and light switches in two rooms below the attic fan, and the smoke puffer didn't get pulled. In order to figure out net free area, I would do Width of inside frame x height of one air flow opening x the amount of lovers or openings? He recommended blown-in insulation and an attic fan if she could'nt afford spray foam. certainly, some installation site should NOT be used. It is made up of 2 very thin layers of most pure aluminum with a thin film of molar in between which makes it non conductive. haha. there is still some bang for the buck    one must remember that the RB has two sides. Attic floor area = 20 ft. x 50 ft. = 1,000 ft. but point well taken (this isnt the main argument against what was said)    second, while radiant energy does continue to be emitted from the underside of the roof deck, that doesnt mean the roofdeck cant be cooled by a little flowing air and that is EXACTLY what happens. A Class II vapor retarder could be kraft-faced fiberglass batt insulation installed at the attic floor with the kraft paper side facing down. and REMEMBER that is with only a 2F degree differential. As long as they have at least as much net free area as the soffit vents, you don't need to install ridge vents. Why bother to pack away the toys for the grandkids when all they'll have is a plastic glob in 20 years? NOTE: Comments are moderated. Gary, That'll actually do some good, unlike the power attic ventilator. Would really like to see BSC or some other research group do more definitive/controlled analysis as I really think this is the root issue. Results in: my gable PAV definitely works. I teach this in building science all the time. The insulation and air sealing keeps out the radiant heat, my interior home temp is fine. As long as the outside air supplied by the fan is of lower temperature (and there is an exit for the air) heat will be removed and these objects will experience a temperature drop. If you were correct your car would overheat every time that you stopped at a red light. The roof travels from the peak to the top edge of the 2nd floor then down to the top edge of the first floor (visualize soffits) (the roof line is not a continuous run like a cape without dormers). @Mark, you are correct, my comment was intended for David-DIYer. The minimum net free ventilating area shall be 1/150 of the area of the vented space. All of a sudden that attic fan isn't needed, anyway. In another home, I found three power attic ventilators in the roof. The precise balance will depend on the balance of resistance of the soffit-vent versus through-ceiling paths (and the through-ceiling path also has resistance on entry to the house—from crawlspace etc). maybe a separate blog topic? Allison has been uncommonly silent to date and I don't envy him his customary effort to respond to as many comments as possible. Other than the air space along the eves and the roof material and an air space at the roof peak, there is no venting. People will write anything these days. According to the National Roofing Contractors Association (NRCA), a power vent with an airflow rate of 1.0 cubic foot per minute per square foot of attic space measured at the attic floor is generally considered to be equivalent to a 1:150 ventilation ratio. Of course you try to make the attic scuttle hole, use air tight trim on your ceiling cans, but it would be foolish to ignore the benefits of a reasonably powered attic fan working in connection with adequate soffit venting. Thank you for your information. i am not saying an AF is for everyone in all climates. This follows the belief, “the more the merrier” or that you can never have too much ventilation. Manufactured versions are available under the names Insullite, Tenmat and Seal-A-Light. so even if the RB was perfectly flat, there is alot of space between many insulation fibers and the RB to give some effect anyway. c) what % does ceiling contribute to total cooling load? My house was built in 1945 and our kitchen ceiling has what I assumed is an attic fan built into it. otherwise a considerable amount of exhaust air bounces off the louvres and comes back into the attic short cycling the exhaist air. If your building enclosure is in good shape, a power attic ventilator is unnecessary. Detractors need to keep in mind that the temperature at top of attic is a lot higher than temp at top of insulation, which is what matters. My apologies for using the rather vague term "power ventilation" in my post. For more on using an attic ridge vent with a power vent, see Combining an Attic Vent Fan with a Roof Ridge Vent. I've been thinking about writing about this as well! AC work is EXPENSIVE. And it's part of the reason that my state, Georgia, has banned power attic ventilators (unless they're solar-powered, which was a concession needed to get the grid-powered fans banned). Stop deceiving people. You should turn off the fan you have, add some soffit vents and see what difference your new insulation and air sealing efforts make. We agree that professional installation is a deal killer for RB. This section contains an extensive list of requirements and conditions that have to be met in order to have an unvented attic. "You cannot cool radiant surfaces with air. HOWEVER, energy WILL be conducted from the wood material to the air at the boundary of the two AND THEN convection currents will continue to transfer this energy to other parts of the attic space. However, a whole-house fan would be a lot more effective if the objective is to avoid the use of A/C. the car radiator is using air to cool a engine block but is 2 steps removed (water cools block, fins cool water, air cools fins). Thinking of disconnecting the fan  by the electrician who installed it. i live in a area with 100+F temps common from May thru Sept. 20yrs ago i installed a gable mounted fan. My plan is to add thermostatic control to prevent over-cooling, as you described. Note that "AT" rated light cans are not really air tight (they're marginally better than non-AT fixtures), and the IC rating (insulation contact) doesn't mean you can cover them in urethane foam. It runs to one or two AM  even on moderate (75 degree) days. In dry climates,  yes have a some ventilation in the attic. the actual time period was most likely greater since that first night the attic temp surely would have been greater past 3am if it hadnt been for the fan exhausting heat. - Radiant Barrier Fundamentals, † My friend Mike Barcik gets credit for this analogy, except that when he tells it, you're lying naked in the sun. But that radiant heat passes through the attic air and hits the solid materials. Get it as soon as Wed, Apr 22. I've seen lots of power attic ventilators, including the one in the top photo. They're dark-colored. Every house is different and the benefits are not always enough to pay for an expensive approach like this, but as far as shear performance I don't think it gets better. For example - we use soffits and ridge vents to move air in attics due to the difference in temperature. A whole house remodel last year required opening up enough walls for electrical confirm this construction. this installation in the above photo could very well be one of the BAD sites. Regardless of where you took the measurement, 110F is not very hot for a vented attic in summer. Ventilation openings shall have a least dimension of 1/16 inch (1.6 mm) minimum and 1/4 inch (6.4 mm) maximum. So, it's natural to think of cooling the attic. i did not have time to read all of this but please be aware the air in the attic is much hotter than the air outside because it is heated by the same radiant effect you are referring to. HVAC outlet temperatures in cooling considerably cooler than under similar conditions, mean radiant temps much more comfortable, HVAC run time reduced, energy bills way down. this is NOT a huge cost. I'm not saying everyone should do it. They also create zones of negative pressure that could pull the AC-cooled air into the attic. Not Allison's #1 Reason, but perhaps his #2 reason: Depressurizing the attic draws cooled air from the house (cooling the attic). Lomanco Power Vent Motor Replacement F0510B2944. For example yesterday was about 88F outside, the 1st floor was a very comfortable 66F, but the 2nd floor was 79F and climbing when I got home at 6PM. so, although the top side gathers dust the bottom side is protected. Your email address will not be published. So getting ready for is next to ...impossible with the level of he. This site uses Akismet to reduce spam. Those walls aren't like the normal exterior walls because the adjacent space is way hotter than outside.