Healthy Indoors Magazine
Issue link: https://hi.healthyindoors.com/i/1398331
by Allison Bailes III, Ph.D. 22 | July 2021 house. Here are some of the questions I've received from readers about their situa- tions followed by my answers. The installers of the new HVAC system told us we "may" need to have a thermo- statically controlled exhaust fan installed to protect the air handler from excessive heat. It's June 11th, 92 deg today, and the tem- perature in the [attic] crawlspace is already well over 100 deg. May I ask your opinion on this specific instance? ~ Steve W., Pennsylvania Steve's HVAC company thinks he needs a powered attic ventilator to protect his air conditioner from attic heat. An uncon- ditioned attic is certainly a bad place to put your heating and cooling system, but a powered attic ventilator will do little to extend its life. I'm not a big fan of radiant barriers because they're cost effectiveness is marginal, but if an attic air conditioner really needed to be protected from heat, you'd do better to reduce the radiant heat by putting a radiant barrier above the unit. 3. They can backdraft a water heater, furnace, or boiler. Back drafting can lead to incomplete combustion, which can lead to carbon monoxide in the air you breathe. 4. They're a solution to the wrong problem. The heat gets into the attic by radiating down from the hot roof deck. Using a fan to address radiant heating is like thinking you can't get a sunburn on a breezy day. Oh, and if your goal is to save money on your cooling bill, they probably won't do that either. Questions from readers Since the earlier articles are closed for comments, I get questions through email and readers filling out the Contact Us form on the website. If you're not immersed in the world of building science, it can be a confusing issue. You may read through the articles and comments and believe your situation is unique and maybe a powered attic ventilator would be good for your I t's time to revisit one of my favorite topics: the powered attic ventilator. Ten years ago I wrote an article titled Don't Let Your Attic Suck— Powered Attic Ventilators Are a Bad Idea. It's got 169 comments and would probably have over a thousand if spammers didn't force me to close comments on older articles. In 2014, I wrote a follow up titled The #1 Reason Powered Attic Ventilators Don't Help. It's got 103 comments. Even as old as they are, those two articles have been viewed 15 thousand times already this month. With the heat wave in the Pacific Northwest this past week, a lot of people are looking for help with cooling. (If that's mainly what you're looking for here, see the Related Articles section below for some good links.) Powered attic ventilators seem to be one option they're looking at. But I also get questions on this topic from time to time, so today I'll explore the issue of whether there's any situation where a powered attic ventilator might be justified. Recap of powered attic ventilator problems You can go back and read the previous articles for more details—and he hundreds of comments—but here's a quick run- down of the problems I described. 1. They pull air from wherever they can get it, including conditioned air from the house. Consequently, some of that cooling they provide to the attic is from your air conditioner. 2. They can suck moist, moldy air up into the house from a basement or crawl space. Is It Ever Helpful to Use a Powered Attic Ventilator?