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  1. #1
    Join Date
    May 2008
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    21

    Conditioned crawl space w/radiant heat

    Hi all ....does anyone have experience/input on utilizing a conditioned crawlspace with radiant floor heat versus bat insulation underneath the radiant piping? I want to try and decide if it is worth the extra expense ....is it better? Is there any problems with this concept? Thx, RH

  2. #2
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,036
    The insulation is there to "direct" the heat up through the floor. If you leave it out you'll have possibly three things happen. 1) You'll spend more money heating the extra space. 2) You'll more than likely have to increase the water temperature in the tubing to deliver the required btu's through the floor to heat the home above it which will cost more due to less efficient operation of the heating plant and that's if you can raise it high enough. 3) You'll have to insulate the crawlspace to the same level that your home is insulated to or you'll loose heat. This includes the floor. And sealing and insulating a crawlspace has a tendancy to increase mold and mildew problems.

    Now....... how much do you think you'll save by not insulating the tubing? Will it save you enough to justify a lifetime of the other added costs?
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  3. #3
    Join Date
    May 2008
    Posts
    21
    The research I have done on conditioned crawlspace (where heavy mill plastic or other even other heavier mil material is used on the ground and sealed around any supports ...then foam insulation is blown against the walls) states that it actually reduces mold and mildew ...and then equalizes the temperature so that the temperature below the radiant floor is not so cold with the result of it drawing or reducing the heat from the radiant tubing. I intend to install a metal heat reflector under the tubing (my thoughts are flashing at this point) to direct the heat upwards from the pex. So the question is whether the conditioned crawl space with its insulation approach is better than the bat insulation under the radiant floor pex installed as I just indicated. To my knowledge the foam insulation is superior to bat insulation ....but more expensive of course. I also do not like the idea of the foam being sprayed between the floor joists under the pex .....and actually it is cheaper to create the whole conditioned crawl space as opposed to this. The issue is how much heat will transfer from the pex and the heat reflector to the conditioned crawl space vs. having bat insulation underneath it with whatever heat loss happens through it if any. Looking for anyone with experience with the concept of a conditioned crawlspace as described. Thx, RH

  4. #4
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,036
    I suggest that you spend some time doing research on the correct methods of installing radiant heating. Direct your research towards the manufactures of the radiant heating products, not the makers of insulation and other items not directly plumbed into the system.

    There are hundreds of mistakes that can be made when installing a system that will not allow for "simple" fixes and in some cases will require most of the system to be taken out and replaced properly. Some of the mistakes can destroy the floor covering. Some of the mistakes will result in the home not coming to set point no matter how long you run it or how high you set the temperature of the water.... and this can be at 10's of degrees away from outdoor design temperature.

    I've been designing and installing radiant heating systems for 20 years and I've fixed just as many DIY jobs as I've installed new ones from scratch. Trust me.... it's always easier and cheaper to do it right the first time.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  5. #5
    Join Date
    May 2008
    Posts
    21
    I agree ....I want to do the radiant right which is why I keep asking all these questions. I am currently waiting on the book "Modern Hydronic Heating for Residential and Light Commercial Buildings" which I will read thorughly before installing. Any other eduction suggestions are welcomed.

    However, the conditioned crawl space seems to be something that is becoming a popular form of insulation in our area ....but of course those are normally forced air systems ....which is why I am trying to get a handle on its use with radiant heat. Thx again, RH

  6. #6
    Join Date
    May 2008
    Posts
    21
    What about using foil backed bubble insulation under the pex ....would that work as well as regular flashing type material for reflection of the heat ....and then provide the needed insulation to prevent heat loss into the conditioned crawl space? Thx again, RH

  7. #7
    Join Date
    Jun 2008
    Location
    Surrey, BC, Canada
    Posts
    35
    I am not sure if I am reading the question right. Do you have a staple up piping in the crawlspace, between the floor joists above , with insulation pressed in from below. If so the insulation should be down approximately 1" from the infloor piping to allow the air space around the pipes to heat. This is not nearly as good as having the piping in light weight concrete inside the floor itself. If you have a staple-up stystem as described above - I would run a seperate line from the boiler, with a zone valve and a couple of baseboard radiators along the walls in the crawlspace. This type of heating is considered a high temp system, but so is a staple up system.

  8. #8
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
    Posts
    1,582
    What type of space are you trying to heat ? Is it a kitchen, if so I would use the bubble wrap leaving a 1" air space and put down a vapor barrier down on the floor of the unconditioned space, and use a tile floor covering if this is in a kitchen will increase your BTU's somewhat and also help retain the heat in the room. Foam insulation up in the floor joist is not gonna do you much in a way of increasing BTU's of the pex as Pex is plastic, now if you were gonna use copper which of course is more expensive vs. pex then this again will increase BTU's and use less energy than pex but it's hardly a trade off at best. If you can I would do the pex with a lightweight concrete on top and use bubble insulation with the air space will be your best option of them all. I have been in a kitchen that had radiant heat with a tile floor and it is the best of the best for heating once everything get up to temp including the furniture and will keep you nice and warm. As suggested read up on warm floor radiant heating from various companies will give you better info than insulation companies will as they only want to sell you more insulation that you really do not need.

  9. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,753
    If you seal your craw;space, and don't have insulation in the joist under the pex. The craw;space is now part of the heat load, and requires more pex, and uses more fuel for heating.

    As the name implies. Its radiant heat. Radiant heat is not like hot air, radiant heat travels down just as easy as it does up.

    Many people have thought since they have a heated basement, they didn't need to have insulation in the joist under the pex. They found out thats not true when their system didn't heat the space when it got colder outside.
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  10. #10
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,036
    One more try on this one.

    I'm sure when you get your book that you'll understand better what people have been trying to explain to you about radiant heating. Chapter 10 is the one you want to understand fully but the whole book is basically required in part to get a good grasp of hydronics in general.

    Best thing that I can suggest for you is to forget everything you've read, heard and basically start over with an open mind. Radiant heating is not an inexpensive type of heat to install. Cutting corners will guaranteed come back to haunt you. Biggest mistake people make is looking for "a way around, or alternative" to doing something that a manufacturer of the tubing documents as the acceptable ways of installing their product.

    A comment on one of your previous posts: The metal/flashing that you were describing you were going to install under the tubing to "reflect" the heat up will not do what you think. The use of the metal materials under the tubing is for dispersion of the heat to a larger area than just the 1/2" diameter of the tubing. It's like the fins on a radiator. In some applications it's desirable to use because the calculations show the water temp needed to heat the space above would potentially create hot spots in the floor directy above the tubing itself. The panels/metal spread the energy out over a larger area and thus have the effect of smoothing out the heat transfer to hopefully a point at which your bare feet can't detect the temperature differences. Also, there are a lot of flooring products and adhesives that can be damaged by concentrated heat energy coming from underneath.

    I know you want to do the very best you can at installing your system and expect it to work flawlessly and that's all anyone giving you information is after also. Good luck reading the book, learning what makes a radiant system function and enjoying the satisfaction of a job well done.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  11. #11
    Join Date
    May 2008
    Posts
    21
    I definitely will be reading the "book" extensively to better understand the install of a hydronic system .....and all this information is really helpful as well. To define again ....the reason I have investigated the conditioned crawlspace is to improve on what I have been led to believe was the traditional way to install the radiant heat ....not to cut corners. In fact ...it is more expensive. The method for the conditioned crawlspace is to put down heavy (10 mil) plastic on the dirt floor and run it up around any support posts as well as the walls of the crawlspace. Next closed cell spray foam is applied to the walls as well as the base of the supports ...creating a closed insulated area ....hence a conditioned crawlspace. I now understand that the radiant heat will not just rise but will also dissipate into to this conditioned crawlspace ....so if I do proceed with it I want to discover the best way to dissipate and radiate the heat into the house instead of the conditioned crawlspace. I believe the conditioned crawlspace to be a good idea ....but if my needs for properly insulating the radiant floor heat take too much of the budget then I may have to forgo it. Keeping in mind that the conditioned crawlspace is an insulator itself .....I thought maybe the foil backed bubble insulation might do the trick for the insulation of the radiant floor and also get rid of the expense of the flashing .....but I now understand that that is there to help dissipate the heat. I definitely do not want to cut corners if I do this and want to do it right. Thx again, RH

  12. #12

    Foil bubble wrap insulation

    Beware of this insulation, also known by one well-known brand name, Reflectix. The FTC has forced them to stop making false claims about its R-value, which they were claiming was R-4 or greater. In reality, this product is about R-1, which is not that great. The radiant benefit should give you a little bit more, but not even close to R-4.

    I would recommend conditioning the crawl, but as part of that you should have some air exchange between the crawl and living space. This is tough with radiant heat. You can find more on this at www.buildingscience.com. If you need to do staple-up radiant, you'll probably want some substantial insulation under it (at least R-19), with foil-facing or FSK facing up.

    Good luck.

    Mark
    RESNET Certified HERS Energy Rater

  13. #13
    Join Date
    May 2008
    Posts
    21
    I talked to a manufacturer last week ....Fi-foil .....about their product whihc is a bubble insulation between a layer of foil on each side. Of course it was the manufacturer of the product .....but he indicated that the air space between the the floor and the joists (where he recommended stapling his insualtion product) is what really created the insulating factor. He said that with 8 inches above the installed insualtion as directed would give an R-16. He confirmed that the product itself did not have a high R value. Any input on this? And why do I need an air exchange with radiant heat utilizing a conditioned crawl space? Thx, RH

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