Comments on: Don’t Let Your Attic Suck – Power Attic Ventilators Are a Bad Idea

By: Mark F

Mark F — Tue, 23 Sep 2014 02:02:41 +0000

David Butler, thank you for
David Butler, thank you for the reply. You make some interesting points but I don't think I can agree with all of them.

First of all, regarding newer more efficient homes, you state "...the risk of depressurizing becomes greater". I take issue with that statement. If a home is well-built it should have less risk of depressurization because the attic will be adequately vented and the ceiling less leaky. In my home it is negligible. And even if it wasn't I would just add some roof vents and caulk or insulate the ceiling pass-throughs (which in my case are limited to few light fixtures, bathroom and stove vents and the whole house fan vents) rather than foregoing the benefits of the cooler attic.

And a well-insulated home is far more likely to be amenable to cooling entirely with fresh air as mine is. This isn't such a rare case. There are entire regions of the country where this is common practice. Admittedly not in the humid southern states but that's not where I (or many others) reside. And as I said the PAV decreases the number of days where the comfort level becomes unbearable to zero in my case. On even the hottest afternoons (sunny, low 100's) indoor temperatures can be kept below 80 degrees making air conditioning completely unnecessary. And even if there were days where the outdoor temperature were even higher and required supplemental air conditioning the usage would be significantly reduced and a much smaller capacity unit would suffice. Still a win energy-wise. This is only possible with a well-insulated home. I also have good windows and added IR films to the south and west facing ones.

And regarding the energy tradeoffs I very much disagree that the PAV would unconditionally use more energy per unit of heat reduction in the living area than the energy required to remove the heat buildup via air conditioning. My ceiling area is 1550 sf and insulation is R-38. If it's say 130 degrees in the attic and 75 degrees in the living area that gives a heat transfer of 2243 BTUs/hr if I'm not mistaken. Now say a 1500 CFM/30W attic fan can cool it to around 100 degrees, reducing the net heat gain to 1019 BTUs/hr. That's a gain equivalent to a 1224 BTU air conditioner rumming at 100% duty cycle, but using only 30W power. Which gives a 40.8 BTU/W efficiency rating.

That's around four times greater than the most efficient air conditioners on the market today I believe. And this imaginary 1224 BTU/hr air conditioner would have to run much longer than an attic fan would, since the PAV shuts of in early evening when the the ambient temperature drops while the the air conditioner would otherwise run hours longer due to the stored heat in the attic that remains even after sundoown. As I said, some of my neighbors' air conditioners run into the early morning hours even though it has long since cooled off outside, which I believe is due entirely to residual heat stored in their attics. I have no doubt that either a whole house fan or PAV (or better, both) would significantly reduce their cooling costs. I'll report back if/when they decide to give it a try.

Again, I will say that I think some newer studies of PAV efficiency are needed. After following up on quite a few of the provided links I found none that were even remotely applicable to my own situation. Or really any that involve drier, higher elevation climates and newer more efficient homes. Or energy-efficient PAVs.
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M. Johnson, I believe that fantech model is a special situation fan (variable speed, external fan) and less efficient than even the cheapest attic ventilator fans you can get at the big box stores. But check out the energy-efficient fans from QuietCool. I also have two of their their whole house fans, one in the main living area and a smaller one in the master BR, which are both super-efficient and extremely quiet. They're supposedly the highest rated ones by the State of California energy commission. From their website:

QuietCool AFG ES-1500 Attic Fan Specifications:
Motor Voltage - 120 V. AC, 60 Hz - Uses A Special AC/DC Brushless Motor For Super Energy Efficiency
Motor Amperage - .25 Amps
Power Consumption - 30 Watts
Motor Speed - 1,100 RPM
Air Flow @0.1" SP - 1560 CFM
CFM/Watt - 52.0 HIGHEST RANK - CA ENERGY COMMISSION
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Adam Stetten, thanks! I may take you up on that beer offer some day. And from reading this thread I can understand your frustration. This so-called "building science" does not seem to be like any kind of science I have been exposed to. Giving an unequivocal, absolute answer and then dismissing all data points that contradict it is more in the realm of dogma than science. That's why I say that more comprehensive and objective studies are needed, especially given the number of real life examples I've seen here which seem to contradict the conventional wisdom. Real science would embrace these and look for a better model to apply in the future.

By: Adam Stetten

Adam Stetten — Mon, 22 Sep 2014 21:03:52 +0000

AGAIN FROM ADAM:
AGAIN FROM ADAM:
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@ M. Johnson regarding the town-homes... There was no problem with any of the town-homes! I can't seem to get that across! The roofs needed to be replaced and the roofers were converting the PAV houses to Ridge-Vent EVEN THOUGH THERE WAS NO VAPOR RETARDER. They were charging for it, and we assume the HOA board members signed a boiler-plate proposal without thinking or even understanding the consequences. Energy bills went up and comfort went down for the homes that had been converted, the data set was small, but the nerdy owners were convinced this was the case.
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I am under attack and everybody thinks I am crazy, so I will start by saying this: when I worked for Southern Energy Management as a HERS Rater, my boss, Maria Kingery taught me something really, really important. She said, “We stand FOR things, not against things.”
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“Don’t Let Your Attic Suck - Power Attic Ventilators Are a Bad Idea”
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The title and content of this post stands clearly AGAINST Powered Attic Ventilators and briefly touches on spray-foam and passive venting but does not give readers any useful guidance IMHO. It doesn't clearly stand FOR anything except [paying an electrician to disable your PAV].
Many years ago, after listening to my colleagues and friend Arnie Katz and reading all this “research” I made similar recommendations and even changed the settings of some PAVs so they pretty much never came on. I regret that, but I am proud that MY MIND IS STILL FLEXIBLE, that I am willing to learn, and that I didn't go public (with duplicate negative posts) on my business's website and create a situation where I can't change my mind or my words. If you wanted to change your mind or take a less negatively charged stance Allison, could you? Oops.
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A few years ago I had a client who's air-conditioning broke at the wrong time. They needed to move some money around, get some bids, and it looked like it was going to be a few days before they got any relief, but they had a single PAV in their attic, almost directly above their attic pull-down stair. I adjusted the PAV for them and we “ran the hell out of it” for a few days with the pull-down open about 5”(with 2 yoga blocks) until they would get their temperature down. When the sun came up they would shut the attic access. The PAV was able to improve their indoor comfort substantially. The “scientists” above think this is impossible/stupid. Get out and try it. Either way in this particular situation everyone was glad they had a PAV and it didn't matter how much energy it used, but knowing what they know now they got an upgraded fan motor. I see these people occasionally and they still apply the “CUPOLA strategy” when they can and seam to be somewhat grateful that they have a money saving strategy after an unfortunate situation. They now have an over-ride switch for their fan, right next to their t-stat. Their attic pull-down has been customized to have an adjustable amount of open-ness.
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There needs to be a separate place for people to go, a new post, that explores the fact that builders have built and continue to build crap. Ridge vent and other passive options can effectively remove moisture, but are nowhere near as effective at removing heat. Even energy star houses with code compliant attic venting, attic air-sealing and R-38 in the attic can still have problems with heat gain in the attic and stored valuables that the occupants would like to keep cool. I have a colleague who refers to all of us energy efficiency people as, “Your People...”, because he thinks there are lots of things we are missing in the “Seal it up tight” mantra we use, which is correct just not the full story if we hope to become sustainable.
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Shouldn't refrigeration be a last resort?
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It is a problem that people use refrigeration as a means to keep their homes comfortable when it is perfectly comfortable outside. All the technology we have these days yet people are not provided A GOOD HOUSEHOLD OR ATTIC VENTILATION STRATEGY unless they are really really adamant and creative and know how awesome it is to have them. The problem is that solar gains, ceiling fans, the fridge, the coffee-pot, cooking, cleaning, showering, the people, the pets, the lighting, the TV's they all use power, generate heat, which rises, and can not get out. Passive attic venting puts a blanket of heat over every house when the sun is shining and for a long time after the sun goes down. Assisted venting turn the tables, allows users control, at the expense of paying for the energy used. To outlaw such a useful device is a horrible abuse of governmental power/resources.
I am not a republican or democrat I hate both equally.
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I am now really motivated to create a knowledge library post that has a different feel, that talks about attic ventilation in a more constructive way, that takes into account that a lot of the suggestions above are undesirable, expensive, unrealistic, and potentially useless in real life. Let's not install a dozen turbine vents or run a box fan in a window. Your readers are REAL PEOPLE needing REAL SOLUTIONS, not a million roof penetrations.
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The world is not a laboratory, you can't extrapolate [old] test house findings to the real world's existing crappy housing stock. In the real world builders are idiots, and meeting code is nothing to brag about.
We don't send our children off to college and instruct them to get a 2.0 gpa and no higher. That is what builders are doing. Shooting for the minimum. People need help and it needs to work.
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I was just in a house with 4 huge gables that had no gable venting. The “storage” in the truss-filled attic was about 4' wide running down the middle, so all the attic R-6 duct-work was hugging the roof, where it can apparently reach 160 degrees, there was a bunch of extra ducting associated with the zoning system. Radiant barrier is not feasible given the calamity, and due to an atmospherically vented appliance I don't think spray foam is a great idea right now. It was nearly 150 degrees in the attic on a relatively cool but sunny day. There was no light showing through the ridge-vent and hardly any through the soffit vents. This client is willing to take out an equity loan for retrofitting their relatively new, relatively uncomfortable home. It is probably going to be significantly cheaper to install a single PAV, and disable the ridge-vent from below, than other alternatives. I hope someday we can experiment with adding returns in every room, and a system to open the return plenum up(with a damper'd duct pointed at and terminating near the PAV) so that the PAV can help assist the CUPOLA effect so that when it is comfortable outside they can TURN OFF THE AIR-CONDITIONER and achieve a more natural kind of comfort. They have a walk-out basement and they could crack the exterior door and let all the heat rise. From my experience this process doesn't need much assistance. We are talking about removing only the top few inches of air from a room every few minutes. We actually don't want this process to be fast. The client wants their home to have the ability to allow heat to rise, and then to be able to stop it with ease.
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The old outdated research that says something like [powered attic ventilator fans use 10 units of power to save 6 units of power] could be redone with today's lower-wattage, stronger, quieter, more intelligent ECM fan motors that use less than one quarter of the power to say that, “powered attic ventilator fans use 2.5 units of power to save 6 units of power”. Even if millions were spent to conclude this I would still think the research was questionable because the way people behave changes the moment their behavior is measured and the world doesn't function like a laboratory. It never will, sorry.
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David Butler is right in his other threads and is super experienced with homes and running the numbers. The math for PAVs can be way off, but just like some of the others, he is now married to the idea that PAVs are bad because it is in black and white. PAV manufacturers withhold information, they use the cheapest motors they can get, they don't even care what the wattage is, and it isn't their problem. If you DO want a PAV an ECM fan motor will sweeten the deal for about $60 and they are usually sold at HVAC supply stores, and yes, of course: FOLLOW ALL OF THE GUIDELINES ABOVE ABOUT PROPER INTAKE VENTING, PROPER AIR-SEALING and INSULATION, AND COMBUSTION SAFETY.
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Since my last comment there's been constructive comments, some good sharing and some nonsense. When folks take a hard stance on a topic, and then put their hard stance online for everyone to see, they tend to take an even harder approach to attacking those who disagree, especially when the opposition comes into enemy territory to do so.

I stand by my initial comments. I have read every article, all the research, every comment, I understand all of that. I just don't operate out of fear or benefit from it enough to perpetuate it.

@ Mark F
Mark F has his own version of home ownership where PAVs are critical to comfort. They save him energy too. Thanks for sharing buddy. If you are ever in Raleigh NC beer is on me.

@ Allison
I have never said anything in support of SOLAR PAVs so both Arnie's article and your mention of it aren't relevant. You repeatedly baffle me with your assumption that (insert “expert” here) is right and everyone else is an idiot.

I have had the pleasure to work with and train with John Tooley and Arnie Katz and Cyrus Dastur, some of the brightest and most prominent building scientist's of our time, and you are obviously extremely surprised that somebody like me is not drinking all of their Kool-Aid. There are a few other things that people at Advanced Energy and other idolized building scientists got wrong. They promote 100% electric homes, even where natural gas is readily available, even in low-income communities, even when large families are involved, and there is no doubt people are taking cold showers right now as a result of it. They promoted this way before heat-pump efficiency/technology started making even a little bit of sense in the winter, in NC, even though they preferred to heat with gas in their own homes. As a result you can walk through low-income “system vision” neighborhoods all over the country during the winter and see heat-pumps “defrosting” even when they are not frozen.

“World Class” Building Scientists have taught me to use negative pressurization during blower door testing, but they never taught me to always check that you won't be pulling in unhealthy air from the crawlspace/attic prior to starting the test, I had to figure that out myself by noticing how dusty homes get during energy audits and HERS ratings, and as a result I don't want or need blower doors and duct-blasters to run a pretty damn good home-performance-contracting business. The proof is in the energy bills.

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Do you use/teach negative pressure testing? You are going to kill someone or make them sick, haha. Do you wear sandals? Do you have long toes? You should remove your sandals and destroy them, they are potentially dangerous. You are so quick to suggest that my actions are going to harm someone and sling your fear-mongering around when all I do is promote healthy housing and help people with sick/wet/costly buildings find resolution. I am not out here to hurt anyone, and I don't appreciate you making this thread so hostile that people with differing opinions are likely scared to jump in. I feel like my job here is done because people seem to be chiming in in support of PAVs or at least experimenting with them.

I know this comment is all over the place but I am fighting an uphill battle against people I have never met who are slinging fear and hatred from all directions. If you are looking for guidance on your poor attic ventilation problem you might want a paid consultation from someone who hasn't made up their mind yet. I likely wont be posting here any more, but will ready any further comments. Thanks for sharing/reading everyone. ~Adam

By: M.Johnson

M.Johnson — Sat, 20 Sep 2014 04:23:24 +0000

I question that a quality fan
I question that a quality fan can move 1500 cfm with 32 watts. Fantech is a top quality manufacturer, and look at the specs on one of their models:
www. fantech.net/RE-10XLT_enus-40230.aspx

Their 526 watt model is rated for 1009 cfm max, if there is zero back pressure. I expect you will sneer at Fantech, but will you share the name of your super efficient fan?

By: David Butler

David Butler — Sat, 20 Sep 2014 02:45:13 +0000

@Mark, I'm not aware of any
@Mark, I'm not aware of any studies on PAV's in efficient homes, but the lessons learned and reported in the older articles and papers apply even more so for more efficient homes. Not only do the potential benefits go down (smaller pie) but the risk of depressurizing becomes greater.

You're correct that some newer models (with ECM motors) are more efficient, but I see no compelling reason to do more studies. When we build homes properly, the ceiling loads become such a small portion of total cooling loads, why bother.

Your previous comment about using a PAV to supplement whole house fans is interesting. As outdoor temperatures rise, there's a point where the WHF won't cut it, so I can see how a PAV might delay or eliminate the need for AC in that case. But there's also be a point where the PAV won't be enough. So there's a limited range of conditions where the cumulative energy consumed by the PAV would be less than cumulative AC energy after factoring in the *much* longer PAV run-time to achieve the desired result. However, I would first consider whether improvements in the ceiling wouldn't be a better value over the long term.

I'll grant you this: If someone in a dry climate doesn't already have an AC, and can use this strategy to forgo that expense -- and remain cool, then that's obviously a good thing. But that's a special case, and there are tons of these things being installed in homes where they do more harm than good. For the most part, I see them as an expensive band-aid.

By: Mark F

Mark F — Fri, 19 Sep 2014 23:18:40 +0000

I've also noticed a scarcity
I've also noticed a scarcity of scientific studies and comprehensive data on the topic of powered attic ventilators. Some of the references commonly cited are decades old and most have extremely small sample sizes and focus on humid southern climates and homes with problems like leaky ceilings and inadequate attic venting causing significant negative pressure. Are there any studies out there that specifically look at potential savings with newer, well-built, well-insulated homes in western US climate zones and with energy-efficient attic fans combined with appropriate passive venting?

By: Mark F

Mark F — Wed, 17 Sep 2014 22:19:11 +0000

Wow! Some great discussion
Wow! Some great discussion here, even if it's a bit heated. Like Adam Stetten, Dr. John and others I also decided to ignore the unconditional black and white conclusion that PAVs are bad and rely on my own judgement, scientific knowledge and assessment of my situation. I installed an attic fan this summer and the result has been stunningly positive.

Here is my situation - dry climate, blazing hot and sunny summer afternoons, cool evenings and nights, newer ranch home, fairly tight, decent ceiling insulation, reasonable attic ventilation, no ductwork in attic. We decided to cool our home entirely with fresh air - no air conditioning or swamp cooler. I installed two quiet energy efficient whole house fans instead.

In the evening as soon as the temperature drops below 75 or so we open up the windows and turn on the fans. Within minutes the house (and attic) have cooled down to ambient temperatures. In the morning we close up the house to contain the cool air and turn off the whole house fans if they are still running.

This system almost worked, but on the hottest summer afternoons (high 90's to low 100's) the house still became uncomfortably hot by late afternoon, sometimes reaching the mid-80's. And with the whole house fans off in the afternoon the attic became unbearably hot. Even with decent insulation a quick calculation showed that heat transfer through the ceiling was adding significant BTU's to the interior. And the ceiling was definitely warmer than the room air temp, which confirmed it. Running the whole house fans was not an option because it would require opening windows and losing the remaining cool air inside.

Long story short the solution was a powered attic fan. The results have been stunning. Since installing it my peak indoor temperatures on the hottest days have been 5-8 degrees cooler than before. The difference is stunning. Before we installed it we were on the edge of breaking down and getting a small air conditioner as a backup. Now there is absolutely no need to do so.

I studied this blog, the comments and looked up many of the links before making my decision. All of the objections to PAVs seem to stem from a very narrow set of assumptions - leaky ceilings, inadequate attic vents, humid climates and so on. I could not find one that reflected my situation or that of many others in my area (both whole house fans and attic fans are popular and effective here).

I've also seen a mention of attic fans consuming as much as 500 watts which blew me away. A modern energy efficient model I looked at is rated at over 1500 CFM with 32 watts energy consumption! The amount of energy you save with one of this cooling your attic by 30-50 degrees will be far more than the air conditioning load to remove the extra heat from your interior if your system is designed well. There's no comparing energy consumption of an efficient fan versus air conditioning. Not to mention that I hear my neighbors' air conditioners running until well after midnight due to the stored heat in their attics. But not having air conditioning at all is the big winner for energy efficiency, and the attic fan was the last piece of the puzzle that enables me to do so without any loss of comfort.

So take all of this discussion with a grain of salt and don't trust any "expert" who believes that one answer is right for every (or even most) situations. And don't be afraid to experiment and trust your own judgement. That's my takeaway.

By: ORLANDO GONZALEZ

ORLANDO GONZALEZ — Wed, 17 Sep 2014 04:23:43 +0000

I LIKE THIS ARTICLE, I WAS
I LIKE THIS ARTICLE, I WAS GOING TO BUY ONE SOLAR POWERED , BUT NOT NOW.
SHOULD I BUY BETTER AN AIR VENT SIMPLE CUT INTO THE END OF THE OOF SIDE WALL OF THE HOUSE?
WOULD THAT BE BETTER OR JUST NOTHING, I ONLY HAVE THE 8 VENT EAV AROUND THE HOUSE?
THANKS LET ME KNOW WHAT YOU THINK?

By: David Butler

David Butler — Sun, 14 Sep 2014 00:04:38 +0000

@Aaron, attic condensation is
@Aaron, attic condensation is a cold weather issue. I understand you have wet winters, but since condensation evidence is isolated to one corner, this is not likely the result of outside humidity.

Here are some questions:

Is that corner of roof more heavily shaded in winter? Is here a bathroom or laundry in that corner or the house? What about a disconnected bath vent, or a bath vent exhausted through the soffit (blow-back)? Or a bulk water issue (roof leak)?

Find the source before prescribing a solution. If it can be confirmed that outside moisture is the cause (unlikely), then you might consider increasing the soffit vent in that area and/or a passive box vent or turbine above that section of the roof.

Note that mold will grow if humidity is high enough, around 70%. Condensation requires 100%, or a bulk water source. So the lack of mold is a clue.

By: Aaron

Aaron — Sat, 13 Sep 2014 06:37:11 +0000

Asking this in the spirit of
Asking this in the spirit of interest and my own attempt at understanding, I wonder if anyone could comment on the use of a PAV in my situation:

10 year old house that is having moisture build up in the attic. We had additional vents added recently but the issue remains. Not so much moisture that mold is an issue (yet) but in one corner of the upstairs there is some evidence of water staining and attributed it to humidity build up. We've had contractors evaluate and have ruled out other sources as best they can. We are in Oregon - so we get long and wet winters (and springs and falls). The advice we got was to add a PAV with a humidity controlled fan.

I have no need to cool the attic or the house using a PAV, we only run the AV 15 days a year because it just isn't that hot most of the time. My use of a PAV would only be to control humidity in the attic.

Thoughts? Thanks!

By: Laura in Chicago

Laura in Chicago — Thu, 11 Sep 2014 16:38:15 +0000

I have the identical question
I have the identical question as Kevin's. Strangely enough, my home fits nearly the same description: hip roof, 160 linear feet of soffit, newly restored ceramic tile roof. Attic is not ventilated, and barely insulated. I am looking to have cellulose insulation blown in (R45-R60 -- as much as possible, given the bitter cold Chicago winters), once I've had a chance to air-seal any penetrations to the attic. There are no ducts in the attic, but a few recessed lights, electric conduit, etc., all of which will be properly sealed. I am also planning to have Attic Foil brand radiant barrier attached to the rafters to deflect summer heat, and later laid out over the insulation to deflect the home's heat/cooling.

My biggest concern at this point is not the heat or coolness of the attic. As much as I intend to seal off the attic (and no, it will not be used for storage or anything at all), my biggest concern is moisture that might still make its way into the attic from the inside of the home. I do not run humidifiers, but even so, moisture from cooking or normal household air will almost certainly find its way to the attic.

I'm assuming my best bet is venting at the soffits, and then perhaps one or more box vents near the top of roof to act as the outtakes. Not sure how to figure the correct placement or number of vents, but if someone has some tips, that would be helpful. The home is a historic, 1-story bungalow, so aesthetics is also very important to me.