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  1. #1
    Join Date
    Sep 2013
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    5

    Question Radiant Heat Under Tiled Soaking Tub?

    I live in Seattle, Washington and have the world's tiniest bathtub. It sucks. So I'm attempting to design and build (ha! I mean "have built") a tiled soaking tub that will be on an outside ground level wall. It gets pretty chilly here and I'd hate to fill up an ice cold tiled tub with hot water only to have it cool quickly because of the cold tile. So I've read about people utilizing radiant heat under tiled shower floors and thought it would be a great idea for the bottom of the tiled tub and maybe even up the back (the part you lean against). I called Sun Touch to ask about that sort of installation and they disavowed any knowledge of anyone doing that because it would be an application that would void the product warranty. I may have been hearing things, but I think I may have heard a nudge, nudge, wink, wink in there somewhere, too. So, has anyone got any ideas about this or know of someone who has done this? Also, how can I efficiently insulate the tub structure from the ground? Styrofoam, closed cell foam, icynene, etc? Thanks!

  2. #2
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,768

    Default Re: Radiant Heat Under Tiled Soaking Tub?

    What does Sun Touch make, the tiled soaking tub or the radiant heat? Do you want to use hydronic or electric radiant heat.

    Tiled soaking tubs are very common in Japan. They do heat the tubs somehow. I don't know how it is done today, but in the old days, they built a wood fire under the tub. Bear in mind, they did not use the tub for washing, only soaking, so they hardly ever changed the water. They bath outside the tub, rinse off and then get in to soak. Those tubs were often pretty small too, about the size of a 55 gallon drum.

    Even today in modern Japan, they still bath outside the tub but I think they change the water more often. Tiled tubs are not being built in Japan as much today though as most Japanese are going to fiberglass or aluminum tubs, mostly fiberglass.

    I would advise against electric resistance radiant heating. If the wires burn out or break, you won't be able to fix them. You also need some protection between the wires and the insulation. The individual wires get a lot hotter than the tubing used for a hydronic system, but they have much less surface area. That could end up melting or burning the insulation.

    Hydronic system with PEX tubing imbedded into the cement backer or thinset and then tile over with insulation behind the cement should work fine. Just keep in mind that you maybe entering uncharted territory here, but then that is how progress is made.

    The last shower install done on TOH put the radiant heat underneath the foam shower base. I don't think that is going to work very well.

  3. #3
    Join Date
    Sep 2013
    Posts
    5

    Default Re: Radiant Heat Under Tiled Soaking Tub?

    Thanks for the advice. I can't believe there isn't someone out there who has done something like this before. I'm thinking you're right and that I should consider doing the under tub heating with a hydronic system as opposed to the electric mats like the kind Sun Touch makes. I was just hoping to do this project in a low budget way instead of the TOH way on the shows with gargantuan budgets!

  4. #4
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,768

    Default Re: Radiant Heat Under Tiled Soaking Tub?

    Another option to consider if you are planning to to have a "Jacuzzi" system built in is to add a water heater to the circulating water.

  5. #5
    Join Date
    Sep 2013
    Posts
    5

    Default Re: Radiant Heat Under Tiled Soaking Tub?

    No, I'm not planning a Jacuzzi tub, just a plain old soaking tub. Maybe I can insulate the heck out of it so that the tile won't leach away so much of the heat from the water so quickly. Any suggestions? Has anyone ever used the Wedi system?

  6. #6
    Join Date
    Mar 2014
    Posts
    1

    Default Re: Radiant Heat Under Tiled Soaking Tub?

    Hi,

    just found this post. Any updates?

    I am also building a tiled soaking tub, 5' square, and was planning to use a radiant loop in the tub floor to try to keep the water warm (I have radiant in half of my house and it works great!).

  7. #7
    Join Date
    Dec 2013
    Location
    Montreal Canada
    Posts
    204

    Default Re: Radiant Heat Under Tiled Soaking Tub?

    Does it ever freeze in Seattle, Washington, If it does your heating pipes could freeze and burst also what about your drain pipe?

  8. #8
    Join Date
    Mar 2014
    Posts
    3

    Default Re: Radiant Heat Under Tiled Soaking Tub?

    I redid our bathroom about 4 years ago and put electric radiant heat in. DO NOT put it under that tub. I have not had any issues with ours and I have it encased in about 250 lbs of thinset and under a Ditra memebrane, but no issues yet. Electric systems can't be run under anything. As previously stated, they get hotter and that could cause a heat buildup and possibly a fire.

  9. #9
    Join Date
    Mar 2014
    Posts
    8

    Thumbs up Re: Radiant Heat Under Tiled Soaking Tub?

    I did this under a tile soaking tub and walk-in shower in Missoula Montana about 2 years ago. I used water - pex because I was already installing it on every floor as a primary heating system with a boiler, circulating pumps, outside temp drop sensor, etc. etc.


    Overall my heating system has been very efficient. I'm not sure I'd go out of the way to install a system like this under a bathtub or shower unless I'm already installing it everywhere-else. Also, I'd recommend against installing it everywhere unless you are staying in the house for a good 5 - 10 years. I'd recommend going with the electric unit if it's just for one area as more of a convenience. Keep in mind that pex / radiant systems take a while to heat up. Expect 30 minutes + before you notice much heat coming from the tile. The system is meant to heat a room up slowly and provide efficient room temp maint. It's not meant to provide instant warm-toe gratification. That's where your electric systems are good.


    All that aside, I do like waking up in the morning and walking into a shower with hot rocks under my feet. But, it's rarely super hot at night unless of course the temperature outside is steadily dropping quickly and the floor is on anyway.

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