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Converting an in-floor system to radiator

vpfalcon Member Posts: 5
I have an infloor heating system in my attached garage, and greenhouse. The system uses a hot water heater which is filled with RV antifreeze. The previous owner installed it. It has worked well the past few years, although I’ve had to top off the RV antifreeze with about 1/2 gallon a week. So I knew there was a leak somewhere in the tubing inside the concrete floor. 
The system has 2 zones and uses 2 1/25 hp pumps. 
The leaks in the concrete floor got quite a bit worse this week. I’m now forced to add 2 gallons per day to hot water heater. I will temporarily switch over to space heaters to keep the plants in the greenhouse alive.
So I’m wondering if I can switch from in-floor to radiator heat in the garage?  Can I divert the antifreeze from the floor to baseboard radiators. I could continue to use the existing hot water heater and pumps. I was thinking about using 4 eight foot long baseboard radiators which are $90 each from HD. 
My other option is 2 5000 watt electric heaters, which would cost quite a bit to run.


  • vpfalcon
    vpfalcon Member Posts: 5

  • Zman
    Zman Member Posts: 7,569
    Well, this is a new one. Just when you think you have seen everything. :o
    To answer your question, you can use many emitters to distribute the heat. Hot water baseboard and fan coils are common ones for a garage.

    In other news:
    • RV antifreeze is for winterizing RV's. It should not be used in heating systems.
    • Heating systems should be pressurized to help keep the air out.
    • Hot water heaters are not designed to be used as space heating appliances
    That being said, If all you are trying to do is heat your garage and greenhouse, install some heaters and carry on. :)
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Zman
    Zman Member Posts: 7,569
    You could isolate the loop to determine which is leaking then abandon just that loop....
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mattmia2
    mattmia2 Member Posts: 9,632
    Oh my.

    RV antifreze is propelyne glycol like hydronic antifreeze but it doesn't have the corrosion prevention package that hydronic antifreeze has.

    Something like panel radiators would likely to be more effective emitters than fin tube baseboard radiators, you would have to run a lot of baseboard radiator and/or run the water at a much higher temp to get equal output to the radiant floor.

    First step is a heat loss calculation so you know what the emitters need to output.
  • Jamie Hall
    Jamie Hall Member Posts: 23,276
    RV antifreeze should be ethanol based, as it is the only one which is non-toxic. You can check the label.

    And ethanol antifreeze does evaporate well below 212, depending on the mix. This is not an issue as an antifreeze -- but it is in a heating system, and you would want to limit your maximum temperature accordingly -- no more than 170 F to be on the safe side.

    However, I can well see that in a greenhouse you want to have a non-toxic antifreeze! So with the exception of the limited temperature, I'd say it was a good choice.

    I'd go for refitting with panel radiators. They have excellent output even at lower temperatures, and you can simply make them bigger along the knee walls of the greenhouse.

    The water heaters are problematic. Even if you limit the temperature to 140, they are going to have a short and miserable life. However, they are what you have -- and when they do die, you cold refit the same greenhouse heating radiators with an LP mod/con to great effect.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • kcopp
    kcopp Member Posts: 4,431
    I would see if you can find the leak... What type of tubing is in the slab? A Flir camera could help find it.
  • mattmia2
    mattmia2 Member Posts: 9,632
    Propylene glycol is non toxic. That is why it is used in hydronic antifreeze, if it were toxic you would need things like rpz backflow preventers and double wall heat exchangers between it and systems that provide dhw or have potable water system makeup water connections.
  • vpfalcon
    vpfalcon Member Posts: 5

  • mattmia2
    mattmia2 Member Posts: 9,632
    kcopp said:

    I would see if you can find the leak... What type of tubing is in the slab? A Flir camera could help find it.

    You might want to pressurize it and see if it is leaking somewhere not in the slab as well, especially if it is hot ethanol it could be evaporating.(although you can probably smell it wherever it is)
  • vpfalcon
    vpfalcon Member Posts: 5
    Thanks for all the great advice.
    I will lower the temperature on the water heater, and see if that helps. If it’s all evaporation that would fix it. I do believe the water heater has been used for the floor heating since the last 90’s, when this system was installed. It’s held up a long time.  I can also isolate the two zones to try to determine which one is leaking. The tubing is a semi hard black plastic and I think it is degrading, there is a purge? Spigot in the greenhouse and when I open it the RV antifreeze that comes out is dirty. 
    I’ve kept the system open during the winters, topping off almost on a daily basis to keep the air out, but there is a valve just below the fill bottle and I’ve closed that today to see if that helps. 
    Thanks again 
  • hot_rod
    hot_rod Member Posts: 22,121
    Some RV antifreeze are propylene glycol, not ideal, but not the worse fluid.
    various alcohols are used as geo antifreeze
    I know someone that uses vodka as a system fluid.
    see if you can limp by on one loop, sounds like polypropylene tube, a common DIY tube

    Radiant  ceilings could be a future retro fit option, plants may like heat from above 
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • vpfalcon
    vpfalcon Member Posts: 5
    I lowered the temperature on the water heater and also closed the valve under the upside down “fill” bottle. I waited 24 hours and checked for antifreeze loss and there was none. After another day, again no fluid loss. 
    I’ve used this garage floor heating system for 4 winters and I always left the valve under the “fill” bottle open. I thought I would I would have “vapor lock “ if I closed that valve and that I would ruin the pumps. I’ve had to add antifreeze regularly every week, and now after I close that pesky valve, the system seems to be airtight and there is no fluid loss. 
    The garage is a nice 64 degrees and, at least for now.... everything seems to be fine!
    I guess the loss may have been due to evaporation all along, and with the closed loop there is no evaporation.
  • mattmia2
    mattmia2 Member Posts: 9,632
    one of the reasons the system should be pressurized is to help prevent the pump from caviatating.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    Is that black polyethylene pipe? 

    Glad to hear you are not losing (evaporating) fluid any longer. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!