Shower Bench Heating

Jamesgang

I'm redoing our masterbath and replacing the old tub shower combo with a glass enclosed tiled shower and bench. I am concerned about the surface temp of the bench. I'm going to be adding a dedicated hot water return for instant hot water as part of the project using a pump powered by the light switch. (We're retired so a timer is out.) The instant hot water system will only be for the master bath.

I'm considering embedding some 1/4" pex loops under the bench top tiles in the modified thinset and running my instant hot water return through the pex loops as a low budget bench heating system. I'm not sure if the water temp will be too high? Or if there's anything else that I'm not considering with this idea. Thanks for any comments.

Alan (California Radiant) Forbes

I would install a 3-way (potable) zone valve controlled by a thermostat with a slab sensor, but I would use 1/2" (potable) PEX.

Jamesgang

That sounds way more complicated than I wanted to do. I think it would be simpler to go electric radiant if involving a thermostat.

GroundUp

Electric resistance cables in an application that has them under a puddle of water 100% of the time? May want to rethink that.. As for your question, yes that can work and has been done quite a bit. The issue though is that the flow rate from your recirc will be diminished pretty bad by necking down to 1/4" tubing. I'd stick with at least 5/16" or better yet 3/8"

Gordy

Electric resistance option.

Tile is porous. It will absorb moisture all the way down to the thinset where your wires are.

However it can be done.

Gsmith

i have an unheated 1-1/4" thick soapstone bench in one shower. It does get a little cold, but the work-around we use is to just spray the bench with the hot water from the shower for a minute or so, then sitting on it is no problem. You do need a shower head on a hose to do this.

JohnNY

If you can make a little manifold of parallel tubes in reverse return (easier than it sounds) you'll negate your reduced flow rate through the smaller tubes. I've done this with ½" tubing with no issues. There's probably a better word here to use there than "negate", but whatever, you'll match your intended recirc flow.
Then again, 10 seconds of shower spray will warm your bench.

Jamesgang

Parallel tubes sounds like a good idea. I don't really have a great distance better the bath and the hw heater so 2 parallel will probably do. I have a location that will remain accessible for the connections to the pex.

Alan (California Radiant) Forbes

Controlling the temperature might be a problem - It could get too hot with constant circulation, no?

But it would be a good experiment. Let us know how it goes.

Make sure you install a crack isolation membrane to prevent the tile from cracking.

Jamesgang

The bench is one of those solid foam ones that are sealed. My thinking is hot glue the tubing. Install the side tiles a little high to create a tray and fill with modified thinset and install the top tiles at the same time.

The house is a A frame with the master in the top, shower location puts part of the shower wall next to an attic crawl. Plumbing is cpvc. I'll put the hw return to pex connections between the wall and insulation accessiblefrom that attic space. Potentially I could add a partial bypass or abandon the whole idea if it's too hot. I wasn't excited about burying all those connections behind a tiled wall anyway

hot_rod

3/8 soft copper works well, small OD and holds its shape well. Pipe with a valve as John suggested and you have some adjustability