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  1. #170
    Costco is selling a solar powered attic fan assembly all in one unit ready to place on a roof for $300. The solar power takes away the need to run electrical though it also means the fan is going to be effective only during daylight hours so if there is any heat load being transferred from the house to the attic the fan will not be extracting it during the night.

    It is not unusual to have poorly installed or incomplete flashing for ducting that ends up pulling attic air into the house which is not good in the winter or the summer and one of the first things I check when installing a new HVAC system for a customer.

  2. #171
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Exclamation No night loaf on the roof.

    Quote Originally Posted by elkhornsun View Post
    Costco is selling a solar powered attic fan assembly all in one unit ready to place on a roof for $300. The solar power takes away the need to run electrical though it also means the fan is going to be effective only during daylight hours so if there is any heat load being transferred from the house to the attic the fan will not be extracting it during the night.
    The attic fanshoudl be able to run at least 14 hours a day which should be more than adequate. Any battery capacity on this unit?
    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

  3. #172
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Wink Of COURSE

    Quote Originally Posted by ampulman View Post
    as a Word document entitled: Shophound's Roof.

    Is that device known as an IR thermometer is it sensitive enough to detect cold spots?
    Definitely, my beer is 34'F.
    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

  4. #173
    Join Date
    Aug 2007
    Location
    Atlanta, Ga
    Posts
    213
    Just wanted to throw this out here...I was a firm believer in PAV's until reading along on this forum. I have done a lot of work over the winter in the attic. Adding insulation...making sure all soffet vents were not blocked. Also, my roof has many ridges, all have ridge vents. Taking the advice from people on this forum, I have added an attic tent, caulked all the penetrations through the top plates and disconnected my PAV. Today it was 96* and sunny...my attic temp reached only 110* Now it is currently 88* outside, my attic temp is also 88*. My upstairs Temp was 76* throughout the day, although my upstairs AC runs contantly from 1pm till 10pm, the humidity is very low. Every pro I have spoken with saids this is normal for a properly sized unit. I have 2 high efficency units(Ruud, 3 ton upstairs 2 ton downstairs) and cannot complain about my electric bill which runs about $50-$60 more than my electric bill in the winter. With my PAV, I could not achieve a temp below 78*. Thanks to all on this forum who know what they are talking about.

    Ask yourself this. Can a sealed attic with a PAV achieve only a 14* temp difference? Or is a well ventilated attic better (and no $$$ wasted on running the fan) Ditch the PAV

  5. #174
    Join Date
    Apr 2002
    Posts
    11,808
    if you sealed your soffit vents and went with something like icynene under the roof deck your attic would be 78F
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  6. #175
    Join Date
    Aug 2007
    Location
    Atlanta, Ga
    Posts
    213
    I have heard that icynene is great stuff...very expensive...would you remove the ridge vents as well?

  7. #176
    Join Date
    Apr 2002
    Posts
    11,808
    if you seal the attic you seal it
    no ridge vent

    if it is gabled insulate the gable also
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  8. #177
    Join Date
    Aug 2007
    Location
    Atlanta, Ga
    Posts
    213
    How does it preform vs. radient barrier?

  9. #178
    Join Date
    Apr 2002
    Posts
    11,808
    Sealed attic is like wearing a condom, radiant barrier is like taking valtrex

    You vent an attic to prevent icycles.


    Now think about it in cooling.

    An attic is a solar collector, the sun beats on it and it gets way hotter than the outdoor air. Then the vents let in humid air. So you have basically have a hot suana above you.

    Now when you seal the attic and insulate the roof deck, you are reducing the solar heat getting in. Radiant barriers make a difference but inside the attic is not the best place for them. If you want something to reduce the solar radiation, put it on top of the roof, it is going to reflect away heat in the first place. Then with insulation under the roof the attic will not be much warmer than the air conditioned space.

    I built a fourplex in hurricane alley. I put the insulation on top of my roof deck, then white roofing above it. It is a gabled roof, so I insulated the gable walls on the inside.



    I only have approximately an R7 roof, so it averaged 81F up there in the attic. Then I conditioned it with about 30 CFM, stays about 79F. I think if you had your AC ducts up there, the duct leaks would suffice

    After a major hurricane here a lot of places had new roofs. A common retrofit was about 6 inches of icynene, so must be roughly equivalent to R19 or so. Typical temperature up there was 78F

    I am in the tropics, been in the attics where they draped bubble wrap under the trusses then nailed down the sheating above the bubble wrap. One had a continuous perforated soffits and then R19 at the bottom of the trusses. Low/mid 80s and humid as hell in there. Was up in one particular attic like that as part of a major investigation into high humidity, When a couple whole house dehumidifiers could not keep up. Culprit was a major return duct leak, drawing in that humid attic air.

    Dehumidifers were wired to run the air handler fans to circulate the dry air. Unfortunately the system with the big return leak was one wired to run with the dehumidifier. Turned out to be a 4 ton drawing in 25% of its air from the attic
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  10. #179
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    Quote Originally Posted by Joe Mascitti View Post
    How does it preform vs. radient barrier?

    Bottom line is this...if you have ducts in the attic, which many homes do, icynene on the roof deck beats radiant barrier hands down. Radiant barrier will keep an attic cooler than without, but a foamed roof deck and sealed attic makes the attic capable of being conditioned space, and not much variance from indooor ambient without it.

    For those owning homes with marginal attic insulation on the attic floor, ducts in the attic, and a budget that excludes foaming the roof deck, you should bear in mind that radiant barrier yields higher energy reduction with marginal insulation on the attic floor than with higher levels of insulation. The spray-on radiant barrier in my own home has at best an emissivity of .22, compared to foil based products better performance at .05. The company who installed the barrier also increased attic insulation to ~R40, which in my opinion is where the largest reduction of heat transfer from attic to house occurred. The radiant barrier helps the ducts deliver more capacity from the cooling coil.

    When you crunch some heat transmission numbers, using a formula like U factor * area * delta T, and measure known R values of various walls and ceilings in your house, it often becomes clear where the largest sources of heat gain are to a house in summer. Transfer from the attic to the house through the ceiling, while noteworthy, is often considerably less than through single pane aluminum frame windows, which went into so many homes over the past forty years or so. Even a shaded single pane job can actually contribute more heat load to a room than the wall and ceiling surfaces combined.
    • 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. #180
    Join Date
    Apr 2002
    Posts
    11,808
    The big gains are the glass and the infiltration or ventilation. Elite spits out a pie chart, pretty good visual. Really emphaszied the window issue like you did on another thread.

    But still, when you look at numbers like that, the attic is a big part of the infiltration, and air from a vented attic will have a lot more enthalpy than 'your design dry bulb and wet bulb'

    My office has the worst scheme possible for an attic here. If you pop a t-bar tile, and get lucky, you see some R-19 friction fit between a couple trusses. The attic is vented, black shingles and a black gable. I am on the west end of the building.

    I was missing a lot of batts and a quick fix was the big sin, staple bubble wrap acorss the bottom of the trusses. Big difference, no penalty from dust yet.

    I should tape some black tape on the under side of the bubble wrap, and then apply some black tape on the under side of the R19 in an adjacent truss space.

    Then get the temperature of the tape with an infrared thermometer.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  12. #181
    Join Date
    Jun 2009
    Location
    Texas
    Posts
    13
    Quote Originally Posted by Joe Mascitti View Post
    Just wanted to throw this out here...I was a firm believer in PAV's until reading along on this forum. I have done a lot of work over the winter in the attic. Adding insulation...making sure all soffet vents were not blocked. Also, my roof has many ridges, all have ridge vents. Taking the advice from people on this forum, I have added an attic tent, caulked all the penetrations through the top plates and disconnected my PAV. Today it was 96* and sunny...my attic temp reached only 110* Now it is currently 88* outside, my attic temp is also 88*. My upstairs Temp was 76* throughout the day, although my upstairs AC runs contantly from 1pm till 10pm, the humidity is very low. Every pro I have spoken with saids this is normal for a properly sized unit. I have 2 high efficency units(Ruud, 3 ton upstairs 2 ton downstairs) and cannot complain about my electric bill which runs about $50-$60 more than my electric bill in the winter. With my PAV, I could not achieve a temp below 78*. Thanks to all on this forum who know what they are talking about.

    Ask yourself this. Can a sealed attic with a PAV achieve only a 14* temp difference? Or is a well ventilated attic better (and no $$$ wasted on running the fan) Ditch the PAV
    Joe, I am curious what your attic temperature was running before you did the work. I have been told by some A/C guys that my attic is the hottest they have ever been in.... Not sure about that, but it was 120 deg this morning at 10AM when the outside temp was about 80 deg. I have been up there before when it was 130-140 and that was on a day when the outside temperature was in the low 90's..... It has been over 100 here past several days, but i have not had chance to check attic temperature.

    I have soffit vents (not sure if they are all open but would presume they are since there has not been any new insulation blown up there since house was built in '90's). I also have the little rectangular vents on top - I think they call them air hawks (???) - but they are not powered vents or turbines, just vents. I have about 5 of those - I think my attic is around 2000 sqft.....

    NO ridge vents and NO PAV's... About 9" of the pink rolled insulation R-30 and I also saw some R-19

    I really don't think my house stays that comfortable and the A/C runs freaking constantly..... Just got a new Trane 4 ton 14 seer last year and think it is a tad undersized (about 2500 sq ft).......

    Curious your thoughts AND ANYONE ELSE'S !!!!! on what are best things to do to help the situation.

  13. #182
    Join Date
    Aug 2007
    Location
    Atlanta, Ga
    Posts
    213
    97* yesterday..my attic peaked at 113.7*...I cannot remember exactly before, but even with the PAV I think I was in the 120's...When I had my roof re-done a few years ago after a big hail storm. I asked the roofer to be sure to put a Full ridge vent on every ridge. Prior only the "Main" roof had one, and it was about 1/2 the length of the ridge line....

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