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  1. #1

    Radiant/Foam/HVAC ?

    I am in the process of considering a HVAC replacement but am wondering about foam and radiant barrier.

    What is the experience is in the real world with paint on radiant barrier under the roof deck? Worth the $ ? (North Tx, 1400 sf frame house)

    Have always thought foam would be great but I understand it's very expensive. If you did radiant, will foam stick and would that be a waste of money? In other words, wouldn't just foam be good enough?

    Just wondering how the ROI works out if I just foamed the crap out of the roof, radiant or not vs replacing the old still working HVAC. Any comments on how well radiant barrier paint and foaming the roof deck have worked out are appreciated. Yes HVAC needs replaced but limited budget and the tax credit will work either way. So if I don't have the bucks to do it all, do I replace the HVAC with something efficient or Foam/barrier the roof ?

    Yeah I know it's a HVAC site but you guys seem to tell it like it is & I know someone out there is doing both for a living.

  2. #2
    Join Date
    Jun 2010
    Location
    Houston, TX
    Posts
    178
    Did you install the radiant barrier in the end?

    Quote Originally Posted by txconsumer View Post
    I am in the process of considering a HVAC replacement but am wondering about foam and radiant barrier.

    What is the experience is in the real world with paint on radiant barrier under the roof deck? Worth the $ ? (North Tx, 1400 sf frame house)

    Have always thought foam would be great but I understand it's very expensive. If you did radiant, will foam stick and would that be a waste of money? In other words, wouldn't just foam be good enough?

    Just wondering how the ROI works out if I just foamed the crap out of the roof, radiant or not vs replacing the old still working HVAC. Any comments on how well radiant barrier paint and foaming the roof deck have worked out are appreciated. Yes HVAC needs replaced but limited budget and the tax credit will work either way. So if I don't have the bucks to do it all, do I replace the HVAC with something efficient or Foam/barrier the roof ?

    Yeah I know it's a HVAC site but you guys seem to tell it like it is & I know someone out there is doing both for a living.

  3. #3
    No but I put foil barrier in a large shed that I have & I think it stinks.
    I didn't notice a big difference for the money, still gets plenty hot in there and it's well insulated.

    For the house, haven't done barrier or foam. Went with a heat pump instead and am awaiting first hot months bill to see if I want to spend the extra $

    Good luck

  4. #4
    Join Date
    Jun 2010
    Location
    Houston, TX
    Posts
    178
    Perhaps it's a matter of ventilation? Did you add ventilation to the shed?

    The radiant barrier kind of channels the heat to the top, but then you need to take it out... that's my understanding. But interesting to know... I'm still on the fence myself as it'd be a major investment considering the size of my attic..


    Quote Originally Posted by txconsumer View Post
    No but I put foil barrier in a large shed that I have & I think it stinks.
    I didn't notice a big difference for the money, still gets plenty hot in there and it's well insulated.

    For the house, haven't done barrier or foam. Went with a heat pump instead and am awaiting first hot months bill to see if I want to spend the extra $

    Good luck

  5. #5
    Join Date
    Mar 2007
    Location
    Madison, Wisconsin
    Posts
    2,263
    Good passive ventilation, combined with insulating only the living/work space (as in do NOT insulate the ceiling, and then insulate the bottom of the roof as well, it is either one or the other) These are the keys to keeping the HVAC bill down!

    Essentially you do not want to make a double wall with dead air space in between. Power vent fans are a poor substitute for a well thought out passive ventilation plan. If at all possible use energy heals at the edge of the roof and use 1/4 inch plywood to make your soffet venting instead of the cheap staple up foam ones. Use blown in insulation(I prefer fiberglass) and make sure your vents don't get plugged by the insulation. Then use a GOOD ridge vent.

    As for radiant barrier, it does only radiant reflection, it does not help with convection or infiltration. At my place I used a radiant barrier on top of the sheeting of my roof, then put my roof material over that. It helps to keep the roof material from heating up quite as much, at least in theory it does. My old house does not have energy heals, but even so I put in plywood vents every third truss and a good ridge vent. These along with a new steel roof, and my house is much cooler in the summer, and I think it helps a little in the winter.
    I r the king of the world!...or at least I get to stand on the roof and look down on the rest of yall

  6. #6
    Join Date
    Jun 2010
    Location
    Houston, TX
    Posts
    178
    Is it a big work to get a ridge vent installed? any cons?

  7. #7
    Join Date
    Mar 2007
    Location
    Madison, Wisconsin
    Posts
    2,263
    Quote Originally Posted by crayx4 View Post
    Is it a big work to get a ridge vent installed? any cons?
    not generally, Most shingle roofs here have them, metal roof it is just as easy.
    I r the king of the world!...or at least I get to stand on the roof and look down on the rest of yall

  8. #8
    Join Date
    Jun 2010
    Location
    Houston, TX
    Posts
    178
    Never noticed one with here in Houston. And all roofs are shingle..

    Quote Originally Posted by Wheelbaron View Post
    not generally, Most shingle roofs here have them, metal roof it is just as easy.

  9. #9
    Join Date
    Mar 2007
    Location
    Madison, Wisconsin
    Posts
    2,263
    Wow?? I wonder why that is??

    Different climate, but it should still make sense...
    I r the king of the world!...or at least I get to stand on the roof and look down on the rest of yall

  10. #10
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,198
    I suspect you are considering closed cell foam on the roof rafters, not your ceiling joist.
    This helps for 2 reasons first it seals the home better and reduces the infiltration and therefore reduces your load Second it puts your attic duct and leaky airhandler in the thermal barrier and therefore again has a good effect on your load.
    Both these reasons may help you cost justify the expensive foam insulation.

    Just make sure you are getting what you are paying for. Get a blower door test before and after the foam job. the results of the second blower door test will allow a good contractor to do a more accurate Man J cooling/ heating load calc that will right-size your unit.
    I'm not sure if the radiant barrier on the foam is doable. Ask a good insulating contractor. I know the DOE just loves the radiant barrier concept.

    Good Luck Cowboy

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