Radiant Heat in Shower?

chaysDecember 11, 2011

We are close to starting on the Master Bath renovation.

My GC is planning to use an old-fashioned rubber membrane in the shower since he has not used Noble or Kerdi before and does not want my shower to be his gunea pig! This is particularly so because we have a 6' neo-angle shower and it may be complicated enough to deal with before trying new materials! This guy dis a fantastic job renovating our basement a few years back, so we want to go with him because he doea a great job and is easy to work with. I get a little, ummm, micro-manage-y with these renovations, so anyone willing to work with me again muct be a keeper!

I believe that he will do a preslope with the rubber membrane on top -- extending 12" up the wall so I think I am OK with the basic plan. I will make sure he uses a poly sheet behind the cement board on the walls.

The question now is how and where does the radiant floor go? The whole bathroom is over our garage so in the winter the floor is REALLY cold! The GC has never put radiant flooring in the shower, so I want to help make sure we do it right! I think he is planning to lay wires in place vs a mat because we have lots of angles in the bathroom.


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I believe that he will do a preslope too, just like you do, since you and I engage in wishful thinking. But then our micromanagement sense takes over. And our spider sense starts tingling too. After all, we don't remember him saying anything about a slope...

I'd talk to him about this now before doing anything else. Whether you micromanage or not.

If you want to micromanage, read a lot about heat transfer. In later posts, this will help you describe the insulation between your garage and the bathroom. And the air barrier. You must know fully and describe completely the structure that separates the bathroom from the garage. I'll state the obvious here: your bathroom floor is the ceiling of a garage. This is now a "building" discussion not a bathroom discussion. I can assume you have joists not a concrete slab. Other than that I have no idea what you have. I'll bet the original builders didn't work too hard at insulating the garage ceiling / bathroom floor. This is based on common knowledge, and it is confirmed by your statement about the floor being cold. Thus, you have to seal it. To get a warm floor you cannot have leaks letting air seep through. The air is invisible and imperceptible, but it is moving through the floor. Sealing it makes it better in terms of heat insulation. Some more real physical insulation will help too. At this point, any heat applied to the floor will produce a very good heat source for the entire room. It IS possible to heat the room with in-floor heat as the sole source of heat; but there is almost no one who has done this in a typical leaky house.

Once you can describe your structure, post it on another forum where you will find a few expert builders.
http://ths.gardenweb.com/forums/remodel/ is a good place.

Read these threads
http://ths.gardenweb.com/forums/load/bath/msg0122215817319.html How Hot?

http://ths.gardenweb.com/forums/load/bath/msg0220103225281.html a few Q's

http://ths.gardenweb.com/forums/load/bath/msg0920104819260.html icy floor

http://ths.gardenweb.com/forums/load/flooring/msg1213190628694.html thin layer to heat

http://ths.gardenweb.com/forums/load/bath/msg1116262914226.html SLC and air leaks

http://ths.gardenweb.com/forums/load/build/msg012231401366.html speed of heat loss

http://ths.gardenweb.com/forums/load/bath/msg0513161429748.html first Q's

http://ths.gardenweb.com/forums/load/kitchbath/msg1112254325274.html heat another thing

http://ths.gardenweb.com/forums/load/bath/msg1000120723905.html feeling cold
(feeling cold but it's not a cold climate = the way the building was built).

You also have to mention your climate zone when you post. Different climates = differences in the way your house structure was built, as far as air barrier and insulation methods are concerned = differences in the right approach to take now.

hope this helps.

    Bookmark   December 12, 2011 at 10:43AM
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Thanks so much for the links, I will check them out.

My house is in MD in a new subdivision - the house is 8 years old (built by Pulte). I am 99% certain that there is insulation in the bathroom floor over the garage. I also live in a town with very strict building codes and tough inspectors. I have the enjineered joists -- they are like 18" deep or something ridiculously tall like that.

My question was more specifically about radiant heat in the shower. Where in the floor/preslope/barrier/mud/tile process does the heated floor go? Also, I spoke to Bain Ultra and they said I can put the radiant heat under the tub also -- what do you all have to say about that?

Thanks again!

    Bookmark   December 12, 2011 at 12:04PM
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I do not know of any electric radiant heat manufacturer that will recommend or even hint that it is OK to have electric radiant heat in a wet area. Hydronic, yes. Electric, no.

    Bookmark   December 12, 2011 at 3:13PM
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electric cables work best when closest to the surface being warmed. This is obvious if you think about the fact that you want more heat in the topmost surface, as much as possible. A couple of counter-arguments can be made to fine tune this statement, but they don't invalidate the statement. Thus, for the shower specifically, and for any floor in general, for the tub specifically and for any surface to be warmed in general, you put the electric heat cables near the topmost layer (if you consider there are layers). All this and more will be clearer and clearer when you read the threads mentioned in the first post.

Some people have crawlspaces under their floor. It might be insulated too. It leaks. Read the "SLC and air leaks" thread if you want to know more now.

In any new house with deep joists and a bathroom above a garage, there WILL be some insulation. But this is an almost meaningless statement. How much, how done. These are the big questions. Read the "SLC and air leaks" thread if you want to reassure yourself why it's important. In terms of ensuring this one aspect of insulation, "strict building codes and tough inspectors" are useless.

    Bookmark   December 12, 2011 at 3:23PM
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Given your GC's lack of knowledge about state of the art waterproofing I would avoid radiant heat in the shower stall. Really not worth the hassle in my opinion to have radiant heat either for in the shower or under the tub. Not remotely close to the bang for the buck you will get investing in a properly laid floor. I would focus on getting the best waterproofing you can in the shower (even if your GC needs to sub the work to someone familiar with Kurdi, the Tile Center in Gaithersburg would be a very good option, and kurdi the entire all non glass walls to the ceiling) and use the money saved to get a dedicated 220/240 line rub from your junction box to a new outlet in your bathroom for your floor. The performance of the 3 systems I have put in using 220/240 is DRAMATICALLY better than standard 120. The hot water in your tub will be all you need as newer tubs have dramatically increased their insulation properties. Just tested out my new Sanijet Cierra last night and over a 40 minute soak it lost about 3 degrees, impressive. When you run the dedicated power line for the floor, you can also run an 8 pound ground wire for your tub that will protect its electronics from our wonderful Maryland thunderstorms (not to mention you if you are in the tub). Most newer Maryland homes have large empty cavities surrounding the cold air returns to the second floor so you can run these lines from your basement junction box through this chase to the attic and down to your bathroom. Any competent electrician will have no problem with this work (I did it myself and had electrician friend check my finished work). If you really want the shower floor to warm the instant you get in than a thermostatic valve with a remote that allows you to turn on the shower to your exact temperature preference from outside the shower stall would be a better way to go. I put Moen's version of this in my Mom's house for her and she loves it but honestly for me the one foot i put in the shower to turn it on and step out for 30 seconds before going in just was not worth the additional cashola. Good luck on your new project, I just finished my master bedroom last night and absolutely love it.

    Bookmark   December 12, 2011 at 3:41PM
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Realize that there are millions of other membraned showers out there, being manufactured, distributed, installed, warrantee and all. All working fine.

kurdi is only one option, but it seems that the internet is full of kirdee happy folk, like promoters. No matter how one spells it.

A liquid membrane that one paints on (by roller or trowel) is a lot easier than an orange sheet that has seams that need sealing. A Wedi style foam board is a lot easier too.

The orange sheet membrane requires a lot of work. It has to be applied with thinset. The seams might produce a wave in the wall. A foam board removes this step and gives you a flat wall. So, in terms of membrane the orange sheet with seams is not the greatest and not the best for all purposes.

    Bookmark   December 12, 2011 at 4:57PM
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I went to a tile store to discuss this - does this sound right?
Mud preslope
Rubber Membrane (extend 12" up wall)
Mud slope
Radiant Floor

We will also put the heat under the granite shower/seat bench.

On the walls, we will either use a poly sheet behind the durock, paint waterproofing on the durock or use Hardiboard, etc.

Does this plan sound good??

Thanks again!

    Bookmark   December 14, 2011 at 1:35PM
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Are you talking about placing electric heating cables in an area that will get wet? Doesn't sound like a good plan to me.

    Bookmark   December 14, 2011 at 3:00PM
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Chays, that sounds great. I hadn't thought of under the shower bench. My GC may hate you. What brand of radiant heat are you using, and if you don't mind, what's the ballpark cost?

I ask because my guy, Big Al, tells me it's gonna cost about $1000 for 100 sq ft including mat and thermostat. I scoffed. We had it in our last bathroom and my frugal hubby wouldn't have approved that cost. But maybe costs have risen in ten years...

I'm in Oakland, doing a gut remodel of a 1935 Cape named Vivian. So far, we've just begun the framing and roughins for electric and plumbing. I kinda need to make a decision quickly so things can move on.

Thanks a bunch to anyone who can lend some insight.
Warmly, Dina

Here is a link that might be useful: Dina Loves

    Bookmark   December 14, 2011 at 3:10PM
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BTW, I'm kinda micro-manage-y, too. Trust but verify is my motto!

It makes for a better end result, I think. For example, Big Al didn't mention adding a thermostatic balance to the shower. But because of the great GW folks here, I knew enough to ask for one.

He probably considers that stepping on his toes but that's better than me getting doused with cold water when the toilet flushes. Just saying...lol

    Bookmark   December 14, 2011 at 3:16PM
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Sounds right if you want to fry yourself or short out an electrical panel. Electric radiant heat doesn't belong in a wet location.

    Bookmark   December 14, 2011 at 3:39PM
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SunTouch makes shielded cable for use in wet locations. Apparently you need to make sure to get the wire rated for wet area uses. I *may* run a separate radiant system (to a separate thermostat - just in case of problems down the road) but I have not decided that yet.

SunTouch specifically allows use in the shower and under the bench. Two tile stores I visited did not think it was unusual at all. Coincidentally, they both sell SunTouch systems.

I have no idea the cost...we are planning to lay the wires instead of a mat since we have a lot of angles in the bathroom (and shower).

    Bookmark   December 14, 2011 at 5:45PM
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fwiw, i would simplify the layers.
any imperfect membrane, as a heat break
radiant layer
the real membrane, e.g. a liquid paint on Hydroban and the kerdi drain

    Bookmark   December 14, 2011 at 10:51PM
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In shower radiant heat is done routinely here. Sun Touch is the brand.

    Bookmark   December 15, 2011 at 7:12PM
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From the FAQ page at SunTouch ...
Can I install the SunTouch in a shower floor?
Yes. Both SunTouch mats and WarmWire are UL listed for installation in a custom shower floor or bench application. Refer to the SunTouch installation manual and WarmWire installation manual for further instructions.


    Bookmark   August 24, 2012 at 11:20AM
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I am looking at purchasing the SunTouch mat 12000630LW from Lowes. I want to *verify* this mat can be used in a shower application. I am planning to use this mat in a tiled curbless shower, so the mat will go under the shower and across into the bath. I see in the FAQ: Can I install the SunTouch in a shower floor?
Yes. Both SunTouch mats and WarmWire are UL listed for installation in a custom shower floor or bench application. Refer to the SunTouch installation manual and WarmWire installation manual for further instructions.

Also, if we insulate extra under the floor between the joists, are we able to use any type of insulation ? i.e. foam instead of fiberglass bats

P.S. What shower floor waterproofing methods are able to be used with this product ?

You are correct, the SunTouch mats can be installed in a custom shower as long as they are embedded in the mortar for the floor covering. I have attached a link to the installation manual (http://www.suntouch.com/mats/) which is located on the left of the page. Download the manual and note the exact sizes will not be noted in this manual as Lowes carrys a 30 wide product, but the construction and materials are exactly the same. Please refer to pages 12 & 13 for complete information.

As far as insulation goes, insulating the bays below the floor covering it is always a good idea. Because the insulation will not have any contact with the heating elements, the insulation type doesnt effect our products. Please feel free to insulate away.

Any shower membrane that is TCNA Approved should be able to be used with our systems. Make sure that any paint on applications do not include any petroleum products as they can damage the wire coatings. Otherwise, check with the store about the best products.

    Bookmark   August 24, 2012 at 12:19PM
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I'm sorry-- I know there are installers who will do it, but there's no way in hell, I'd even consider taking on the liability of installing ANYTHING electric in a shower pan. Especially when the wires are to be located INSIDE the membrane, where they're SURE to be exposed to moisture!! Moisture plus metal plus lime (from the mortar) equals deterioration. Sooner or later, that system will fail, and someone will, at best, get a real quick perm, and at worst, die. No thank you.

If you want to warm up the shower pan before you get in, run the hot water for a minute or two.

    Bookmark   August 25, 2012 at 9:21AM
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