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  1. #274
    Installing ridge vents are much more difficult on high pitched roofs. I installed one on a 12/12 roof once and I thought I would have to call the fire department to get me down off the roof. You can use a carbide tip blade on a circilar saw and cut away the area neccessary. What one has to watch for is trying to hang on straddling the ridge and not cut away so much material that the roof vent will not cover. It not very difficult to cut away too much. Also one needs to use the screws with rubber gasket. The ones like they use on Tin roofs. Roofing tacks could back out and driving them in on unsupported plywood could damage the plywood.

  2. #275
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
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    3,304
    When you say "one against the other" Brian could you please restate that? I just did not understand what you were saying. I am hoping it would not be too much trouble for you to look up and read the FSEC case study. If I remember right the published research suggests a potential 6% AC savings but the fan energy will probably exceed that unless solar powered. Will have to re-read the FSEC paper which actually focuses on solar fans, to remember its conclusions.

    6% is problematic because it is so small most experimentalists will have trouble measuring it, let alone most electric customers. The paper suggests other variables are much greater for heat gain into the house or attic ducts. I haven't given up hope somebody might demonstrate a set of circumstances where some hours of PAV operation might save more than they cost -- but have not seen it yet.

    Regards -- Pstu

  3. #276
    Join Date
    Mar 2008
    Location
    Long Beach, CA
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    3,730
    Pstu,
    What I meant was to not test the PAV vs. AC effectiveness by having both of them on at the same time. Test the PAV and AC separately. See which one uses more energy to reduce int temp.

    People claim dual pane windows are not energy efficient or have no effect on energy bills. That is to say they do not insulate better and have no effect on maintaining indoor temps. I think that claim is rubbish.

    Brian

  4. #277
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    14,915
    Quote Originally Posted by Brian GC View Post
    It is by overwhelming consensus that powered attic ventilators are discouraged here. But I am still waiting for more than opinions on theory. I want to see test results or hear from someone who actually turned one on in a well ventilated attic and watched their indoor temp rise (w or w/o AC). To my following of this thread that still has not been furnished.

    People like the roofer and others here have seen them lower indoor temps. Where are the people who have actually seen them do the opposite in a well ventilated attic?
    How about a 5500 sq. ft. with three 1200 CFM PAV's and over 1500 square inches net free area of dormer vents down low on the roof line.
    The house has had some sealing of recessed light fixtures and major thermal bypass issues sealed, but was still being depressurized to -11 Pa by the PAV's.
    The initial complaint from the customer was that their downstairs family room, living room, dining room and kitchen didn't cool well.
    After verifying that the HVAC equipment and zone controls were all working properly, I turned off the PAV's.
    The house immediately went to a neutral pressure, and within a few minutes it felt noticeably better.
    I talked to the customer again about 2 weeks later, when it was even hotter out, and they are no longer having a problem cooling that part of the house.

    This was actually a repeat problem with this house. In the summer of 2008 I found the house being depressurized to -26 pa, but it had no intake.
    The roofer came back and nstalled a whole mess of little dormer vents low on the roof line for intake, but I didn't get called back out to test it until we had the unusual humidity + heat we are having this year.

    I've solved the lack of cooling problem people were having in dozens of houses by turning off their PAV. Some didn't have near enough intake, but many had way more than the usual that is recommended.

    This isn't even taking into account the danger posed by PAV's in homes that have natural draft combustion appliances...
    Last edited by mark beiser; 07-28-2010 at 05:10 PM.
    If more government is the answer, then it's a really stupid question.

  5. #278
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,376
    Quote Originally Posted by Brian GC View Post
    It is by overwhelming consensus that powered attic ventilators are discouraged here. But I am still waiting for more than opinions on theory. I want to see test results or hear from someone who actually turned one on in a well ventilated attic and watched their indoor temp rise (w or w/o AC). To my following of this thread that still has not been furnished.

    People like the roofer and others here have seen them lower indoor temps. Where are the people who have actually seen them do the opposite in a well ventilated attic?
    Brian, you don't need to wait for anyone to do a study on this. You can conduct a study of your own. Purchase a Testo 510 digital manometer. They are not very expensive. Go to a house with a powered attic ventilator. Set up your manometer to measure indoor air pressure in relation to outdoor air pressure, measuring in pascals. Be sure all windows and doors in the house are closed tightly. Get an average reading from the manometer on whether it is negative or positive to outdoors prior to turning on the attic fan. Then have someone turn the fan on. If the house either goes negative or noticeably more negative with the fan on, you then know the fan is drawing some air out of the house. If it does not, you can then know there is either a decent airtight seal between attic and house, or the attic is very well provisioned with ventilation screens, louvers, etc. so the amount of air drawn from the house is negligible.

    I will say that not every house will perform the same with a running powered ventilator in the attic. Some will really draw air from the house, others not so much to not at all. It is worth measuring, regardless, as if there is a problem it is worth fixing if the homeowner is gung ho for using an attic ventilator. However, getting an air tight seal between an attic and a house is very tricky, so I would expect to see more of what Mark discussed in his last post above.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #279
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    If i can figure out how to convert a 1 gigabyte MPEG to something more manageable to upload to my web domain, I'll post a 27 minute training video I have on the unintended side effects of PAV's.
    It would answer pretty much all of the questions.
    If more government is the answer, then it's a really stupid question.

  7. #280
    Join Date
    Jun 2007
    Location
    Bucks Co PA
    Posts
    367
    Quote Originally Posted by geoss54 View Post
    I just finished reading alot of pages on this thread-very informative, but I really cannot come to a consensus of ridge vents vs. power vent.
    I have a 2 story townhouse between 2 other townhouses. Presently there is a power vent, but has never worked since I moved here. There are 2 soffit vents opossite each other.
    It is about time to replace my roof. Roofer told me he prefers putting in a power vent, more in the middle and higher up than the present one. He said he finds it does help in the summer(he did mention that my attic was one of the hotter ones he was in).
    I originally wanted a ridge vent.
    There are foam baffles at the soffits which allow air entry. I did call an insulation company for them to verify insulation thickness and whether baffles are set correctly and air is flowing well.
    Providing I get more insulation in and soffits properly open, which is the better way to go?-power fan or ridge vent. please, all ideas greatly appreciated. We are in the Philadelphia area.
    Thank you George
    I have both.

    My PAV was installed when the house was built in 1988. At one time I was worried about power consumption so I adjusted the PAV to turn on at over 100* instead of 90* - 95*.

    My second floor was always hot so I decided to put in a bypass timer on the PAV. My bedrooms are 5* cooler when the PAV is running vs not. With the timer I also run the PAV for a few hours after sunset to bring in cool night air.

    A few years ago I had the roof replaced and the PAV replaced as well, plus a ridge vent installed. I also have soffit and gable vents to help air flow.

    My house was "sealed" as it was being built so leakage into attic is reduced (I have no way of knowing if it is 100%). They did a blower door test after settlement so I know they did a good job sealing.

    .

  8. #281
    Join Date
    Aug 2009
    Posts
    1,127
    Quote Originally Posted by mark beiser View Post
    If i can figure out how to convert a 1 gigabyte MPEG to something more manageable to upload to my web domain, I'll post a 27 minute training video I have on the unintended side effects of PAV's.
    It would answer pretty much all of the questions.
    Try uploading it to YouTube. You can then imbed the video on your site. That will also drive a bit of traffic from YouTube to your own domain.

  9. #282
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    Quote Originally Posted by Jack2007 View Post
    My second floor was always hot so I decided to put in a bypass timer on the PAV. My bedrooms are 5* cooler when the PAV is running vs not.
    It would be interesting to have a chance to actually test your house, but I'm in Texas, so that isn't going to happen.

    My suspicion is that the rooms being cooler with the PAV running has very little to do with a reduction in attic temperature, and everything to do with the PAV changing how air moves through the structure with the PAV on vs with it off.
    Most likely the PAV is just masking one problem with a different "problem".
    If more government is the answer, then it's a really stupid question.

  10. #283
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,376
    Quote Originally Posted by mark beiser View Post
    It would be interesting to have a chance to actually test your house, but I'm in Texas, so that isn't going to happen.

    My suspicion is that the rooms being cooler with the PAV running has very little to do with a reduction in attic temperature, and everything to do with the PAV changing how air moves through the structure with the PAV on vs with it off.
    Most likely the PAV is just masking one problem with a different "problem".
    Perhaps drawing air up from the cooler downstairs regions?

    This thread must be a cat! It has nine lives! It keeps coming back from the dead!
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  11. #284
    Join Date
    Mar 2008
    Location
    Long Beach, CA
    Posts
    3,730
    Mark,
    You have definitely solved some problems caused by PAVs. But the example you site has far more PAV volume (3,600cfm) than is needed, wouldn’t you say? If you disconnected two instead of three wouldn’t that be the better way to pinpoint the problem? One PAV would probably have the same affect on attic temp and little-to-no effect on negative pressure. Also, if the house has thick blown-in attic insulation a PAV will have little effect. And if only one part of the house was adversely affected by the PAVs them that would show a significant envelope leak in that area. Were other parts of the house unaffected and possibly the upstairs was cooler with the PAVs on?

    As the subsequent poster said he gets positive results from his. Just like you would like to understand how his PAV achieves this, your customer’s house should be better tested so such a broad brush is not used to discount them. I’d start by saying three PAVs is overkill in itself.

    Brian

  12. #285
    Join Date
    Mar 2008
    Location
    Long Beach, CA
    Posts
    3,730
    Quote Originally Posted by shophound View Post
    This thread must be a cat! It has nine lives! It keeps coming back from the dead!
    Because it is complicated. A lot of things can make a PAV help or negatively affect living conditions. The problem lies in when a PAV is found to cause a problem; too much is read into it. Houses that benefit from them should be studied by the disclaimers to see they are not all bad.

    Brian

  13. #286
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    14,915
    Quote Originally Posted by Brian GC View Post
    Mark,
    You have definitely solved some problems caused by PAVs. But the example you site has far more PAV volume (3,600cfm) than is needed, wouldn’t you say? If you disconnected two instead of three wouldn’t that be the better way to pinpoint the problem? One PAV would probably have the same affect on attic temp and little-to-no effect on negative pressure. Also, if the house has thick blown-in attic insulation a PAV will have little effect. And if only one part of the house was adversely affected by the PAVs them that would show a significant envelope leak in that area. Were other parts of the house unaffected and possibly the upstairs was cooler with the PAVs on?
    Turning one or 2 of them off would only lower the depressurization, not eliminate it.
    There is a lot of very solid building science that has been done on the subject, and many case studies done by people that have the luxury of the time and budget to set a bunch of instruments up and play with different scenarios in homes.

    The universal consensus among those people is that powered attic ventilation is almost always bad, for a variety of reasons. How bad depends on a lot of factors.

    http://www.advancedenergy.org/buildi...%20Studies.pdf

    The problems associated with PAV's that have come to light in the last couple of decades are finally starting to be addressed in building codes.
    Beginning January 1 of 2011, Georgia's new energy codes BAN them completely from use in any new construction.
    http://www.energyvanguard.com/blog-b...-BPI/?Tag=IECC


    If you have something that shows positive benefits from PAV's, besides anecdotal accounts from people that don't really have a basic understanding of how air and heat move through buildings, I'd love to see it.
    If more government is the answer, then it's a really stupid question.

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