Radiant heat question


Hi,
I have a question for anyone having actual experience with a floor based radiant heat system.
I'm planning on installing a hydronic between-the-joists system. It will use PEX fastened to the underside of the subfloor. The person who'll be helping me with the install, and has installed these systems before says that the aluminum heat diffusers you can apply along with the tubing are useless, especially if you're using water heated to about 100F. I've been reading Siegenthaler's book on the subject and he's absolutely in favor of their use.
Does anyone have any comments? My biggest concerns are 1) will the system be more efficient and able to react faster when needed, and 2) will you get hot stripes on the surface of the finished floor without them possibly leading to premature degradation of the hardwood flooring finish.
FYI, I plan on using mostly hardwood flooring (some tile). Subfloor is 3/4" advantech. House is mostly one floor with a full basement. Joists are 16" on center.
Thanks for your input.
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guessing: your local answer may be directly related to your climate and temperature swings of the basement. nice cutaways at: http://www.healthyheating.com/Page%2055/Page_55_g_radiant_sys.htm no mention of the diffusers at: http://www.neoheat.com/expert-zone/wet-systems/neoheat--flow-range-design.html
Just Me wrote:

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Just Me wrote:

With hardwood floors you want to try to equalize the heat distribution underneath the floor. Hardwood floors expand and contract with temperature and humidity and the radiant amplifies the expansion and contraction. The hotter areas will have larger gaps and that can tend to look off. Use the diffusers.
R
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It is critical that the joist cavities are insulated with reflective insulation. Haven't used it myself, so I'm not exactly answering your question, but this is what I am hearing from our plumbing supply house in Duluth, MN. If it works here, it ought to work anywhere.

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Heating engineers spent a lot of money on R & D to come up with the ideal method of heating the floors. What has your friend done for testing? Use the diffusers.
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#1. if your water is only going to be 100 degrees, don't bother. #2. if you don't "radiate" the heat out from the tubing, what's the point? the aluminum plates are essential for this type of install.
--
Steve Barker


"Just Me" <kenk228@adelphiadotnet> wrote in message
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Steve Barker LT wrote:

#1 and #2 seem to offer conflicting advice. What are you recommending?
R
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So I've seen these diffusers which look basically like a piece of sheet metal with a channel formed to fit the PEX tubing. My guess is that you pay a pretty hefty premium for the form-fit. What about just fastening flat metal to the underside of the subfloor, then fastening the PEX to the metal.. It may not be 100% as efficient as the formed diffusers, but if you get 80% of the value for 20% of the cost it might be worth considering. Also, I would guess that a flat piece which is *between* the PEX and the subfloor will reduce striping *more* than the form fit diffusers. Just seems intuitive to me. Anyone have an opinion?

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