The PAV in our 20+ year old house died last year. Thinking it to be essential equipment, I had it replaced. The handyman purchased the most powerful PAV which would fit. I know it's powerful, because everytime that sucker kicked on, it sounded like a garbage truck was rumbling down the street.

OK, it's moving a lot of air. That's its job. Fine. About six weeks later, we needed AC maintenance, and given the age of our current A/C, they offered us a free assessment on the cost of replacement, when the time comes. The HVAC company we use employs nice and thorough people. During the walkthrough, I lamented the noise the new PAV made, and his response was to say man, you don't really need that thing and if you want, I'll disconnect it while I'm in the attic. He told me the power consumed by these PAVs is not worth the cooling they provide. There was more to the explanation, but he convinced me and he disconnected it.

Two things I've noticed this summer so far- a lower power bill is number one, so I'm thinking he was correct in his assessment. The other thing I've noticed is that without the PAV hooked up, the initial flow of air out of the ducts when the A/C kicks on is noticeably warm. It makes sense- the attic is hotter, therefore the ducts will be hotter, and the air inside, of course. However, this goes away within a few seconds, and then the A/C blows as cold as it ever has.

Do any of you guys have any experience with this kind of thing? Speaking stricly as someone ignorant of most HVAC stuff, it's counter-intuitive to me that disconnecting the PAV gives me a lower electric bill.

Maybe it was sucking your AC cooled air right out and the system struggled to keep up as a result?


I’m not an HVAC expert but I know from my dad who had a 40 year commercial HVAC career that it’s all about balancing the system.

I think the PAV was doing just as the HVAC guy said- it was using a whole lot of electricity.

Had a few AC people tell me the same thing, that it's a waste of Electricity, looked at getting a couple of solar powered units but we never did the install. One thing they said is they can pull cool air from inside the house through existing ducts or openings as well as pull air in through vents that normally exhaust air if they are close to a ridge or roof vent.

This is one of the responses from Googlization

Do powered attic ventilators work?

Although power attic ventilators can provide relief in the summer, how they go about doing that is often not ideal or cost-effective. For one, they can steal air from the conditioned space of the home, forcing air conditioning units to work harder, use more energy and, therefore, raise utility bills

I had issues with condensation in the winter due to no vapor barrier (home built in the 1890s) and inadequate attic insulation (only 12" in MN) I added a vapor barrier and additional 24" of cellulose insulation. I added powered attic fan at the same time to prevent excess condensation (yes all bath fans etc were properly vented) just to cover my bases. I have it connected to a thermo/humidistat so it runs during the hot part of the day or if the humidity is high. Like most homes in MN - our air handling equipment (other than the heat pump/compressor) is in the basement.

We had two attic exhaust fans. When the roof needed to be replaced, the roofing guy advised us to remove them. I don't remember his exact explanation, but the overview was that we would have better cooling at lower cost without those fans.

We put in a couple of solar attic vent fans about 10 years ago. No power cost, and they don't spin very fast so there's no noise objection.

You may have great insulation between the floor of the attic and your top floor ceiling - in that case, the temperature of the air in the attic wasn't a drag on your AC and the power drain of the electric vent fan was really not providing much value, just as your HVAC tech suggested.

The most important thing is sufficient attic insulation. When I had this done it cut my AC bill dramatically. We had an attic fan in Wisconsin when we had no AC. It helped a lot. It might be nice to be able to turn on the PAV if your AC stops working.

It's certainly possible that the PAV was stealing cool air. The A/C does seem to be more efficient now, when I would have thought just the opposite would be true.

Well, at least if we ever sell this house, it has a brand new PAV which only needs to have the power reconnected. If I'd left the old one in place, I'd probably be replacing it in advance of a home inspection, so, no harm.

It's just a fan, can't use a huge amount of electricity.

One argument is it pulls cool air out of the living space... bull feathers... unless you have a really crappy poorly sealed house.

I put in a boat load of those things upon customer request back during my contracting days but never advised either way as to their benefit.

I replaced the one in this house when it failed largely because we have a ton of storage in the attic and if it keeps it a tad cooler it is probabally better on the stuff.

It used to be a big feel good fad to have one, thinking it did great things, it's actually probably a draw... they have fallen out of favor largely.

My advice if you already have one...
Adjust the thermostat until it only runs on the hottest of days and call it a day.

No, but I looked into having one installed the first time I lived in Houston. I had a brand new house, but my bills were higher than expected. After some research, I arrived at the some conclusion in that they were not necessary for my situation. Generally, they're unnecessary if you have good insulation and good ventilation to begin with (e.g. ridge vent and unobstructed soffit vents). One reason why they frequently get taken out when a new roof is installed is they fix the ventilation issue passively (e.g. add soffit vents, add baffles between roof and insulation so air actually flows from soffit vents, add roof vents, add ridge vents, etc) and the expensive band-aid (i.e. powered attic ventilator) is no longer needed.

quote:

Originally posted by tatortodd:
Unnecessary if you have good ventilation to begin with (e.g. ridge vent and unobstructed soffit vents).

We've got that stuff.

quote:

Originally posted by cparktd:
It's just a fan, can't use a huge amount of electricity.

One argument is it pulls cool air out of the living space... bull feathers... unless you have a really crappy poorly sealed house.

So, then, what is your explanation for what I've outlined in this thread?

Para we didn’t usually install Powered roof vents because they weren’t really necessary if the attic venting was constructed properly.

Most of these powered vent have some sort of thermostat so that you could adjust the temperature that starts it. Most of the time this would be set to about 140 degrees or so and should only come on for a few hours or so and even then at a relatively slow speed. You should not hear it normally.

Beside the power consumption, a PAV can do more harm than good by disrupting air flow through the attic and creating dead zones.

If the passive ventilation was done properly, a powered unit is unnecessary, at best.

I had a PAV for many years in a house with no Air Conditioning and under those circumstances, in a house with proper venting in the attic, it will cool a house tremendously. Not as well as AC, but very well.

Powered attic fans are not even allowed for new construction by the Georgia Energy Code anymore, fwiw. And haven't been since 2011.

The science is that the fan actually pulls more conditioned air from your house than from the outside. So it makes your AC work harder, plus the power that the fan itself is consuming.

https://www.energyvanguard.com...georgia-energy-code/

In my area they were causing attic fires so I disconnected mine (I had a coworker who's brother was a contractor and he had made a lot of repairs after fires). I put radiant barrier in my attic and that lowered the temp dramatically. Now the ridge vents will allow air flow through the attic and it does not get excessively hot, no fan is needed.

When I remodeled my house approx. 25+ years ago, I had an attic fan installed in my den and master bedroom. They work great for me here in Az. In the spring and fall, our nights cool down nicely and one can open a window and turn the fan on low, and it will bring in the fresh cool air.

Also, there have been times when I had odors(cooking, etc) in the house that I wanted to eliminate. Open the patio door and turn on the fans. In no time the odors were gone.

I like mine and use them throughout the year. They are cheaper to run than A/C in my part of the Country.

quote:

Originally posted by GT-40DOC:
When I remodeled my house approx. 25+ years ago, I had an attic fan installed in my den and master bedroom. They work great for me here in Az. In the spring and fall, our nights cool down nicely and one can open a window and turn the fan on low, and it will bring in the fresh cool air.

Also, there have been times when I had odors(cooking, etc) in the house that I wanted to eliminate. Open the patio door and turn on the fans. In no time the odors were gone.

I like mine and use them throughout the year. They are cheaper to run than A/C in my part of the Country.

This is a different thing... aka a "whole house fan." This is meant for ventilating the actual living space. Works well for dry air locales better than the humid deep south. What Para describes is only ventilating the attic.