Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Need advice on hot water loop in bath floor

Tom_128 Member Posts: 1
Hello. I'm new to this site, but I have heard great things about the knowledge that lives here.

I have a 90-yr old 2.5 story home with a 9-yr old gas boiler w/pump, and cast iron radiators. I have gutted my bath, and removed the radiator there. The bath is about 90sf, L-shaped. The radiator was fed off a 3/4" supply and return tee. No radiators downstream of this bath. A bedroom is fed off the other side of the tees.

My plan is to run 5/16" Hepex in loops spaced 6" apart on top of a new 3/4" T&G subfloor, and then pour self leveling compound on the HEpex so that I get about 1/2" of cover over the top of the tube.

I understand that 180deg boiler water is too hot for a comfortable floor. My intention is to run 1/2" Hepex supply and return lines from the existing tees to my drop-in tub surround (ie cabinet). In there, I plan to install a zone valve which is controlled by a T-stat on the wall with a probe in the floor. The thinking being that the floor will heat whenever the main system is running (I have no separate zones in the house), but that the T-stat can be programmed to shut the zone valve at a max. temperature so the floor doesn't get too warm). I've found a T-stat of this type that allows a high limit setting.

Questions: will this system operate properly. Do I need a mixing valve if I rely on the T-stat to set the high limit for closing the zone valve? Should I place a small sediment filter before the zone valve to catch any crud that may be in the system (I don't want to clog 5/16" Hepex)? Any recommendations for a zone valve and/or sediment filter. I need a quiet zone valve. Finally, do I need a separate pump for this arrangement, or will the pump at the boiler adequately circulate water through the the floor loops?

I really appreciate your advice and experience. Thank you very much.



  • kpc_73
    kpc_73 Member Posts: 26
    won't work...

    too much head pressure to get flow. You really need to run a separate zone w/ its own circ. back to the basement...
    It is such a small zone that electric may be a better choice.kpc
  • EJ hoffman
    EJ hoffman Member Posts: 126

    Pump sizing is your issue,use 3/4 pipe, and for the temp figure out if you really get 180 up to the radiators I bet you max out at 140-160. I have done this and just used the return off a towel warmer to dump some heat into the room and allow for cooler temps into the floor.
  • Paul Pollets
    Paul Pollets Member Posts: 3,656

    Oventrop makes the "UniBox" for this particular design. Simply remove the radiator, pipe in the supply and return from the radiator stubs to the Unibox, run Pex to the floors(with an 02 barrier) on 6 " centers, and embedd. I'd be using 3/8" rather than 5/16" tubing. You may be able to find some earlier Wall posts on this topic by searching "Oventrop UniBox". The Unibox has a built in setpoint control with limiter.

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • bruce_21
    bruce_21 Member Posts: 241

    I'd put some sort of aluminum heat transfer plate either under or over the pex before the 1/2 inch mud goes down to spread the heat and reduce the chance of hot spots.
This discussion has been closed.