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Thread: How warm can hydronic floors get?

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  1. #1
    DIY Junior Member bandrewfox's Avatar
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    Default How warm can hydronic floors get?

    Hi,

    I have already installed part of this system, but I am worried that the floors won't get warm enough for someone in the family who loves really warm (80 deg) tile floors in the bathroom. Here's my setup:

    Wirsbo/Aquapex 1/2" tubing
    *** Wirsbo Joist Trak - 2 parallel per joist bay ***
    3/4" old "ship lap" subfloor
    5/8" new plywood subfloor
    Tile flooring

    *** Main source of heat is forced air furnace - I am not relying on this system to warm the rooms.

    I am planning on using the floor heating as the return tubing for my hot water recirculation pump. So, I will get a non-iron recirc pump and the hot water heater will be the same one I use for consuming potable water.

    Does anyone have any experience in a similar setup? I would prefer to keep the HWH at 120deg for anti-scald purposes.

    Is it possible to warm these tile floors to 80 degrees? Are there any spec sheets/calculators for figuring this out?

    As always, thanks so much!

  2. #2
    In the Trades Tom Sawyer's Avatar
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    You have a lot of money? Heating the floor with a water heater is going to cost you a fortune. 120 degrees probably will not get you 80 at the tile. You will have to bump the water temp to around 160 and use a tempering valve at the fixtures.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    You've got a LOT of mass there, and wood is a fair insulator...to get the floors warm, you'll need fairly significant water temps when doing it from underneath with staple up materials. It's easier to do when embedded IN the floor, not under it.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Junior Member bandrewfox's Avatar
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    Thanks for your feedback. I got my plans for the "open direct" system from these guys: http://www.radiantec.com/faq/faq04.php

    They seem to be telling me that it is an efficient way to go and that 80 degree floor might be possible with 130 degree water. Then again, they are trying to sell me something, so maybe I shouldn't believe them.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    The number of tubes, the temperature of the water, the velocity of the water, and the thermal mass between the heat coil and the finished floor, ALL affect the final temperature. BUT, the one thing you do NOT have is a temperature limiting device. The return circulation water will be slightly less than the water heater's setting because of heat loss, but it could eventually approximate it, and since it is probably running 24/7, the floor should get warmer and warmer, then HOT, which could be unacceptable.
    Licensed residential and commercial plumber

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    Keep in mind that if you get the floor to 80-degrees and keep it there, eventually, the room will get close to that temperature as well, especially if it is not regulated and you are relying on forced air to warm the home. The real goal should be to get the floors warm. Good insulation and sealing of leaks can help a lot.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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