Comments on: Is It Ever Helpful to Use a Powered Attic Ventilator?

By: Marco Bovo

Marco Bovo — Mon, 08 Aug 2022 10:41:29 +0000

In reply to William Rossiter. I'm sure that someone already asked this, but I couldn't find the answer. So does this mean we're better off closing the vent altogether? What should we do with the existing power ventilator?

By: William Rossiter

William Rossiter — Sun, 07 Aug 2022 15:26:42 +0000

My one-story Montana house has the typical A-frame attic, unused for storage and never accessed, under an asphalt-shingle roof. No AC, no ductwork, no venting into the attic. It’s sealed from the rest of the building with only a 3’x3′ tightly-fitted trapdoor allowing access. Doesn’t it make sense to ventilate the attic in the summer to keep the air cooler and carry off some of the radiant heat generated by the sun on the asphalt? A fan in some electrical devices like a microwave oven cools the works by circulating cool air around the heat-radiating elements–tubes, heat sink fins, etc. Why doesn’t the same heat-transfer effect apply to cool air carrying off radiant heat in an attic? My attic fan recently went dead and I’m thinking of replacing it. Good idea?

By: Thomas Dugan

Thomas Dugan — Thu, 04 Aug 2022 13:41:27 +0000

Accepted practices for home ventilation changed, of course, with the introduction of Central AC. Prior to that, double hung windows, operable transoms over doors, whole house fans (I am from Michigan and had them frequently), etc. A “breathing” house was called normal.
Without AC, attic fans make perfect sense to me as there is no risk of pulling cooled air up into the attic.
Obviously, the issue created by AC is the temperature differential and dew points. Now we have to keep the warm air from ever meeting up with the cool air. I.E. very tight houses.

By: Dan

Dan — Thu, 04 Aug 2022 02:04:57 +0000

Hi Allison, great article!

But we’re still debating if we should install an attic fan in the dormer of our cape cod. It gets really hot up there in the summer. We have gable vents on each side of the house. We just reinsulated one of the rooms in the dormer with rockwool (ceiling is not covered with drywall yet). We don’t have central AC, but we’re considering adding a mini split system.

Does it make sense to add an attic fan in this case? What about a radiant barrier instead?

Thanks!!

By: Jeff

Jeff — Sun, 24 Jul 2022 14:25:56 +0000

My elderly friend lives in southern California in a 2700 sf ranch style, open beam house with 12 foot gabled ceilings, no attic. There is no insulation. The interior temp of the ceiling surface can exceed 100 degrees on a hot day, essentially a 2700 sf whole house radiator. She has 2 central hvac units, but hot air gets trapped at the high points of the ceiling. She lives on social security and can’t afford to replace the roof to add insulation., and insulating the ceiling is not an option. I was going to suggest a whole house fan to evacuate the (blazing hot) air trapped in the area at the peak of the gable, but your writings condemning attic fans while praising whole house fans leave me wondering why a whole house fan would not cause the same problems as an attic fan, eg removing the cooled air, causing backdrafts etc.?

By: smith p

smith p — Thu, 30 Jun 2022 23:41:19 +0000

NW Arkansas resident. 5 yr old custom home w HVAC in attic with ducts suspended half way between the roof deck and floor. can’t put in radiant barrier per a contractor who just put in r42 due to some insultation settling/rafter exposure (it has helped some).

Was going to put a solar fan in but now not so sure. HVAC can’t keep up when its 90 and sunny w temp set at 75. It’ll run 45 min/hour between 3 and 7p. Ducts are insulated (not sure if its r6 or r8) and i suspect radiant/ambient heat is killing the cold air.

What can i do to improve the efficiency? Wrap the air handler? Is there better duct insulation?

By: chris

chris — Tue, 28 Jun 2022 03:28:21 +0000

Middle Tn – we used 2 PAV to replace all our ridge vents when we got a new roof – roughly 5300 sf house – 3 stories plus high pitch attic / roof. Choppy roof that had very short LF of ridge vents. Our 2nd story duct work is in the attic, getting hot… PAV may not help with the radient heat, but if its 110 degrees instead of 145 than I figure it’s better. My first goal was to reduce the heat entering from the attic into 2nd story, and reduce the heat entering the attic ductwork thru convection or radiant. Wrapping the ductwork or foaming/ sealing the attic was not cost efficient for me. A $350 attic fan may be good enuf – for me. It may be a wash cost wise, but if my AC can ‘keep up’ on 100 degree days upstairs, I’m happy. PS – house has good intake ventilation in the soffits. Sometimes an analog truck is better than a Tesla…good luck.

By: Thomas

Thomas — Fri, 13 May 2022 12:27:05 +0000

In reply to Chad. In coastal NC, in the evenings and overnight, with the temperature drop, RH maxes out and there is condensation everywhere. Wouldn't the fan be pulling in that saturated air as well?

By: John Proctor

John Proctor — Thu, 12 May 2022 20:01:49 +0000

Chad, I have not checked your calculations, but there are other reasons to not have the attic ventilator. I was standing next to a natural gas furnace checking for CO. All was good, very low. Then the attic ventilator went on, the meter went off scale and I reached over and turned off the gas. Felling very bad, I walked into the front yard and barfed my guts out.
Some houses are very connected between the attic and the mechanical room. As I am sure you know a depressurized mechanical room is a bad thing.

By: Chad

Chad — Wed, 11 May 2022 21:24:58 +0000

To help answer the question presented by the article, I think there is definitely something to be said for powered attic ventilation for areas with a combination of high heat and humidity. While I agree it is the wrong solution to the problem taken at the article’s chosen scope limited to “heat” and discrediting the marketing behind attic ventilation products (which isn’t hard to do). If your attic has passive ventilation but still creeps above 20-30 degrees over ambient in 100 degree summers with high humidity (90%+), your enemy isn’t heat–it’s moisture, especially if your air handler is up there. 130+ degree air can hold more moisture than you think, and all that moisture stays inside the attic when it finally cools during the night. As the hot attic air cools at night, the relative humidity increases. Since heat is no longer being used to “move” the air through the passive vents in the attic, the relative humidity will continue to rise with a much higher dew point than outside air. Given that, a powered ventilation to replace the cubic volume of the attic per 1-1.5 hour ran at a few intervals of the day wouldn’t be a bad investment. Your attic will still be hot, but moisture would no longer be a concern.