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Surface temp sensor for warm floor boiler?

moondog Member Posts: 1
Hey guys I have a question about radiant heat. Situation is: I have a 65,000 BTU condensing boiler providing radiant heat only, through four zones, but no individual zone control. Boiler is controlled through a Delta controls panel as opposed to a standard thermostat. There is a very old slab sensor (don't even know where it is in the building though!), and when the slab temperature falls below the programmed setpoint, central heating call is sent to the boiler to turn on.

My problem is that the existing slab sensor is nowhere near the actual surface temp of the warm floor. Slab sensor will say 76, but then an infared temp gun pointed at the floor will read close to 100. I don't really have a way of calibrating the existing sensor, and I don't want to drill a new sensor into the floor. The building is a dog kennel for puppies, and customer is pretty set on trying to keep a constant surface temperature of the floor at around 85 degrees (tough to do!). They don't give a hoot what my slab sensor says, they are all about using that infared gun, and they freak out if we go above 90. The other problem is that the floor temp set point can only be adjusted by logging onto the Delta controls systems via a desktop, and then changing the programming, not something I can have the customer do on the regular, so I really wish I had just a regular thermostat controller inside of the building.

Why can't I just get a thermostat with a surface temp sensor that I stick on the surface of the floor in an innocuous spot? My dumb plumber's brain is envisioning an aquastat with the probe duct taped down to the ground and some insulation over it! Does such a thing exist? I'm not having any luck finding anything like that online. I'm a plumber who is pretty comfortable messing around with the boiler but warm floor controls aren't something I'm very familiar with. I'm used to controlling boilers and circulating pumps via pipe temperature, so just wondering if I can do the same with a floor temp.

TL;DR At the end of the day all I want to do is create a 24volt DC signal when a surface temperature falls below 85 degrees, and when the surface temp goes above 85 degrees I want the 24 volts DC to go away. Can this be done?

Thanks for any help or ideas you guys might have. I don't have a lot of radiant heat experience so a part of me is wondering if I just asked a really stupid question haha!


  • hot_rod
    hot_rod Member Posts: 22,157
    Use a radiant specific thermostat, with slab sensor. You need to read air and slab to prevent over-heating the space on mild days.

    I like this type where you can set a not to exceed slab temperature.

    Depending on the location you want more than just a taped down sensor, build a copper well with some tube and some tabs to get a solid mount to the slab if you cannot gets into the slab.

    Dogs need a cool spot to control their body temperature, hopefully they have a pallet or raised platform for the pups to get off a hot floor like that, that 85 seems way to high to me

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream