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  1. #14
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,164
    from other forum:
    oh...from other forum:
    The fan is a large attic ventilation fan near the ridge of the roof. The roof has two gable vents on either end and lots of small round soffit vents.

    pav probably doesn't come on in winter..depends on what it is set to.
    but it will...when operating... depressurize the attic. exacerbates duct/return
    leaks and leaks from attic into house...the one (yay!) recessed light, the
    oversized cuts at bath fans..and top plate leaks.
    disable the pav & when you replace it, use passive vents.

    and remember..this is a hole in the roof...air in...air out.

    I hear you about the gaskets...but the way to stop the leak comming out
    of the slots for plugs. baby proof things you put in outlets to keep kids from
    sticking stuff in the outlets. put the piece of foam gasket that you usually
    throw away on the baby proof plug & put it in the outlet.
    thats a Zero Draft tip btw. (credit where it is due)

    interesting reading between both forums.
    questions are really flowing now!!

    as for foam...call some local companies for pricing. if you can measure roof sq ft
    (or even if you can't) they can give you a sq ft pricing. estimates are usually free.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  2. #15
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,164
    oops, sorry bout that!
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  3. #16
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Reading all this again, id focus on the ductwork. Leaky ducts in the attic could be pushing a lot of air out the house and causing a big jump in bills. Many new construction have flex run by the lowest bidder. that means slap it in quick, usually by a helper wirh little training or experience.


    Sent from my SGPT12 using Tapatalk 2

  4. #17
    Join Date
    Mar 2013
    Posts
    24
    mbarson, my hot water heater is electric. The only drafting appliance I have is my basement propane furnace. It's a Trane XB80. I think it has a powered flue.

    I'll call around and see if I can find a company that will do duct testing. The energy audit company didn't recommend it at the time because the ducting in my attic looks a lot like my basement. Large main rectangular insulated trunk line down the center of the attic with short round insulated flex ducts leading to the boots in the ceiling. The audit lady said she's never seen an attic installation like mine. She said she almost always sees small boxes with round flex ducts all over the attic. So she thought it looked like a very tight installation. But we all know looks can be deceiving!

    At this point I'll try anything though! I even went around the attic fluffing the insulation trying to find black insulation that would indicate an air leak. I couldn't really find any black insulation in places other than the leaks the audit company pointed out.

    I'll also call around and get some foam estimates. I'm afraid the foam will be in the 8K or up range. The insulation company wanted $1,800 for the extra blown in fiberglass. I have an unfinished basement and they gave me a quote to foam seal my rim joist and that was $1,300! So I couldn't even imagine a whole attic!

    energy_rater_La, it's funny you mention the baby safety plugs: My 16 month old just the other day decided he liked plugging things in like mom and dad. So I just started plugging in the safety plugs all over the house. Great idea on using the round throw out piece with the safety plug! You'll def get credit for that one!

    The one thing I'm curious with on the attic duct system leaking: Would there be a difference between the air coming in when the system is on vs off? Since it got cold and somewhat windy this evening, I've got my nice cold draft coming up through my cooktop downdraft vent. The amount of air coming up doesn't seem any different with the attic furnace on or off. Could it just be I have a constant static loss on the duct system, or should the stack effect be amplified with the attic furnace on?


    Thanks again!

  5. #18
    Join Date
    Mar 2013
    Posts
    24
    I may have found a possible problem.

    I just went to do a quick gap check on the two returns and when I removed the filter from the smaller of the two returns a lot of cold air came pouring out of the return. The inside of the large return was warm to the touch, the small return was freezing cold. I'm talking about the area of the return boot right past where the filter sits.

    I remember checking both returns when I was in the attic two weekends ago and both are connected and there are no breaks. Also, when I turn the attic air handler on, the air sucks nice and strong from the smaller return. I'm wondering if I have a strange heat loop going on. The two returns connect to the air handler via a little box on end of the unit. The large return that sits right next to the handler has a very short round insulated run to the side of the box. The smaller return is connected to the top of the box and runs up into the top of the rafters and down to the return boot about 10' away. It's connected like a "L".

    I wonder if when the air handler is off the hot air from the house is going up into the larger return into the little box on the end of the handler. Then up into the smaller return duct where the air cools then falls back into the living space. It's like a little convection circuit. The two returns aren't that far apart on the ceiling. The large return is in the hallway right outside the bedroom the smaller return is located.

    However, this doesn't really explain the stack effect because the air should be balanced since it should be a closed system. Is that a right assumption? Hey I'm grabbing at anything now!

    I'll definitely see if I can find an energy auditor who can look at the duct system. Either way, I probably shouldn't have a blast of cold air coming out of one of the returns and not the other.

    Thanks!

  6. #19
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,320
    Some photos of what you're seeing may help this conversation a lot.

    If the ducts and air handler in the attic are leaky, it will affect the house pressurization/depressurization when the unit runs and when it is off. Return leakage from the attic greater than supply leakage into the attic will pressurize the house when the system runs. Supply leakage to the attic greater than return leakage from the attic will depressurize the house when the system runs. If the ducts and air handler are tight, or leakage on both sides is about equal, the net pressurization on the house is about neutral.

    I'm reminded of an article written by Dr. Joe Lstiburek at buildingscience dot com. In it he says, "A blower door measures the characteristics of the house, not the leakage rate of the house in service". What I think he means is that a blower door test delivers a number, such as "When we depressurize the house 50 pascals, it is leaking at this rate per minute". That shows you how leaky your house is (a characteristic), but it does not tell you where the leaks are, or how the house will leak in the real world. In the real world, you can have a cold norther blasting against the north and west sides of your house, with the east and south sides in a leeward state. Meaning the north and west walls are leaking air into the house, while the east and south walls are leaking air from the house to the outdoors. What that also means is that the high winds can cause the house to leak at a rate more or less severely than the blower door test revealed. Combine this with stack effect, and you have a house leaking in multiple directions. A "complex three dimensional movement of air in buildings", as it's been called.

    All a blower door test does is state "When we depressurized/pressurized your house to a determined level (commonly 50 pascals), it leaked at "x" cubic feet per minute. Real world conditions can exceed that leak rate, because nature knows no limits on what pressures it may apply to your house.

    The article referenced above, while a bit technical, can be found here:

    http://www.buildingscience.com/docum...t-and-airtight
    • 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.

  7. #20
    Join Date
    Jan 2007
    Location
    Minneapolis, MN
    Posts
    415
    I'm glad you don't have a gas water heater. You could peel back some duct insulation to see what it looks like on the joints. I would be surprised if it was sealed with mastic. Without being there it is difficult to access the whole house. There are many dynamic things going on that should be checked. Is there a Home Performance company in your area? Probably someone with BPI.ORG training. You need someone with the experience and equipment to make an accurate determination.

    On the returns the cold air is coming from somewhere, I would try to track that down. The unit should be isolated from the outside. And as requested pictures could be helpful. Perhaps the negative pressure is not from stack effect or the ducts. Cold air should not be coming in from the return. It is hard to say from here! I would make sure the ducts are sealed or have them sealed if not.

    As far as insulation goes you don't need spray foam. I only recommend spray foam for difficult areas that blown insulation would be too hard to install. Also I do not like fiberglass blown insulation. The best performance is from cellulose. Keep looking for a good contractor. The better ones have diagnostic equipment to quantify their results.

    You could also try finding the leaks yourself. An inexpensive theatrical smoke machine you can purchase from party stores will allow you to see the air moving in your house. That may lead to the direction the air is leaving the house.I don't mean to fill the house completely with smoke, just enough to watch it move.

    Keep giving us more info.

  8. #21
    Join Date
    Oct 2004
    Location
    So Cal
    Posts
    3,501
    Negative pressure in house (the title of your thread) would point me 1st to look at the duct system & leakage.
    Had one last week that was so bad on supply side that when the furnace came on, it would cause all the smoke from fireplace to fill the room.
    I'd slow down on throwing a bunches of fixes in the mix & find out why your home is going negative.
    Duct blaster by a HERS rater is where I'd start 1st.

  9. #22
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,272
    Quote Originally Posted by energy_rater_La View Post
    when you put in the whole house system, this doesn't address the
    stack effect, this is a fresh air exchange system.
    this allows you to continue to tighten the house, with fresh air
    being provided by whsystem.

    best of luck.
    So, why wouldn't mechanical ventilation mitigate negative pressure?

    April Aire model 8126 does not seem to be an EXCHANGE system.

    http://www.aprilaire.com/index.php?z...y=16&item=8126
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  10. #23
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,164
    www.resnet.us
    for energy rater in your area.
    we do duct testing on every job.
    talk to several raters and get someone with
    experience in existing homes. discuss the issues
    you've shared here.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  11. #24
    Join Date
    Jul 2007
    Location
    Delaware
    Posts
    3,824
    You can not make a house to tight

  12. #25
    Join Date
    Mar 2013
    Posts
    24
    Thanks for the input. I'm going to call around and get a duct blasting done. From the site that energy_rater_la posted there seem to be quite a few in my area so it shouldn't be too hard to find someone.

    Also, as requested I'm going to take some video/pics of my attic and ducts and post it. I agree, a picture is worth so much more.

    I purchased one of the those Black and Decker thermal leak detectors:
    http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

    I found that there was a 14.1 degree difference between the ceiling next to the return and the filter in the return. 65.3 ceiling, 51.2 aimed at the return duct. I also found similar differences when I aimed it at most of my supply ducts. Only two supply ducts didn't have any drastic temp difference.

    So maybe my duct system is the problem. However, wouldn't I expect the ducts to be colder since they're technically in unconditioned space? But 14 degrees does seem drastic!

    I hope to get home tomorrow before it's dark so I can get some good photos of the attic.

    Thanks again!

  13. #26
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,164
    take some pictures of the returns from both outside the return
    and inside if possible. also, check where plenums connect to equipment.

    looking forward to the pictures.
    I had that black & decker temp gun..someone borrowed it...now just have raytech.
    oh well...

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

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