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Radiant heat in floor using using Radiator system??

mhopkins1 Member Posts: 3
I want to put in radiant heat in a bath that I am planning to remodel. My old house has radiators, which I love. What kind of issue's will I have? Is this is even possible. Maybe temperature, flow, zone valve, could all be issue's. My present system is one zone only. Maybe I should just stay with the existing radiator. Anybody have any thoughts on this?


  • You can install a tempering valve (to reduce the water temperature), pump and a pump relay for tubing in the mortar bed.
    Or you can install an electric radiant mat under the tile.
    Often wrong, never in doubt.
  • Jamie Hall
    Jamie Hall Member Posts: 18,941
    Well... got to admit that just keeping the radiator would be simpler. However... I expect that with the proper piping (treat the radiant floor as a secondary zone with its own pump and mixing valves) you could probably get it to work. It depends some on how your present system is controlled. If the existing system is on outdoor reset, and runs all the time anyway, it would be less of a hassle -- but you would still need the secondary loop, mixing valve, and pump and temperature control for that loop.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • And you don't want to micro-zone that bathroom. You may need to install a low-loss header to keep the boiler happy.
    Often wrong, never in doubt.
  • mhopkins1
    mhopkins1 Member Posts: 3
    Don't really like electric heat, but the mat idea sounds interesting I'll research that. I think my first choice would be a secondary loop. Thank you both for your quick response.
  • hot_rod
    hot_rod Member Posts: 16,307
    With electric cable or mat, you just need to do the area where you stand or walk, not the entire square footage.

    What size is the room, how much is outside wall? If this will be the only heat source maybe do a load calc on the room.

    Nice about electric you can quickly warm the area and use set back & floor sensors to dial it in to your use. Use it in shoulder seasons without firing the boiler also.

    Bathrooms and kitchens are the two best areas for floor warming in my mind. Electric towel warmers are another nice option.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mhopkins1
    mhopkins1 Member Posts: 3
    The electric mat is looking like a better solution. Thanks for the input.
  • Paul Pollets
    Paul Pollets Member Posts: 3,509
    The Oventrop UniBox converts a radiator to a RF zone without having to add a pump, relay or control. https://www.oventrop.com/en-US/products/productgroups/?g=13.b
  • The Oventrop UniBox converts a radiator to a RF zone without having to add a pump, relay or control. https://www.oventrop.com/en-US/products/productgroups/?g=13.b

    Looking at the schematic, you still need a mixing valve and a pump, no?
    This would be a good product for when you need room control of a heating system when you can't get a thermostat wire back to the mechanical room. You probably see it more in an institutional setting.

    Often wrong, never in doubt.
  • Paul Pollets
    Paul Pollets Member Posts: 3,509
    The schematic presumes there's a radiant load on boiler. When the boiler piping is existing for radiators, the Unibox is a mixing device and stand-alone, without a pump. I've used this application with as many as 3 loops on a manifold.
  • delta T
    delta T Member Posts: 870
    Just a thought.....what about installing a hydronic towel warmer where the radiator is?

    The simplest way (assuming that there is room for this above the radiator) would be to connect to the existing pipes coming through the floor and install a towel warmer on the wall behind the rad with surface mount copper or steel pipes that can be painted or boxed in somehow for aesthetic purposes. You would need to take into account what the room load is, how the system is piped, (series, parallel, home-run, monoflow?), what temperature you are running at and how the boiler is controlled.

    Installing a thermostatic radiator valve with a bypass to control the room temperature and effectively 'zone' your bathroom is an option too, and would give you the greatest flexibility in regards to tying this into an existing system and still being able to control the output.

    Runtal makes some good ones that won't break the bank, If sized properly it will work just as well as your existing radiator, but will have a much lower profile, and you will have hot towels every time you get out of the shower.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,249
    edited June 2018
    I’m just trying to understand this.

    If there’s no call for the radiators to turn on, the boiler won’t fire and the pump will be off. How does the system know if the room with the Unibox wants heat since they don’t communicate?

    And I don’t see any way that the Unibox is doing any mixing since there’s no mixing valve inside. The mixing valve (and pump) has to be installed by others before it gets to the Unibox.

    Maybe I should retire.
    Often wrong, never in doubt.
  • Paul Pollets
    Paul Pollets Member Posts: 3,509
    A TRV built in to the device regulates the heat. It works best if the boiler control uses constant circulation.
  • Steamhead
    Steamhead Member Posts: 15,334
    If this is an old gravity system, this may work fitfully if at all. @mhopkins1, how big is the existing radiator and what size pipes are feeding it?

    Also, I don't like electric floor mats in wet rooms like bathrooms, since they can pose a shock hazard if they get wet. Also, if they stop working, you have to tear up the floor to fix them.

    I'd keep the radiator, and get it refinished if needed.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service