Anti freeze

[Stephen C]

I plan to install radiant heat in my 40 year old 800 square foot home on shore of Georgen Bay . I would like to use a tankless water heater for this project . I am concerned about damage from freezing during power failure or during any breakdown .
Can I protect from freezing the heating system by using anti freeze all the time in closed loop system ?
I see some units are fussy about what they will run . Rheem for example states their unit is only for potable water . They also state their units are are not for home heating . Why ?
I worked on industrial chillers that stored ice at night to air condition office buildings during the day . They used glycol and water mix similar to automotive anti freeze without all the other additives used in cars .
Do any tankless manufactures talk heating antifreeze ?

[jadnashua]

Tankless systems are engineered to heat potable water, so any antifreeze would make that water deadly to drink. Also, most are not designed for potentially continuous use 24/7, which might happen during a cold spell. Then, most do not have a huge volume capability and may contain an internal restrictor. A boiler is designed for this use...similar, but not the same. A few can be used for this application, and still have a warranty, but is some cases, that warranty is shortened significantly verses use as originally designed to heat potable water. Also, keep in mind that with any use of antifreeze, it carries with it an efficency hit as it does not transfer heat as effectively as pure water does (course, you'd want that for both a boiler and a HW source like the tankless if you're going to turn the heat off in the winter).

[Stephen C]

Thank you very much for your reply Jadnashua . I did not think of the reduced heat transfer of anti freeze compared to water . I will need more transfer plates and maybe some baseboard rads . I am not an engineer and I do not work in this field . Your input is appreciated . Reduced thermal capacity could also possibly lead to boiling problem in the tankless heater .

It makes sense that some ( maybe all ) tankless units cannot run continuously . I was told by several contractors that I would need 60 ,000 btu for a forced air system . I think the tankless unit will be 3 times that capacity to relieve overloading . Heater will be overcapacity so it should warm up fast . When return water sensor is warm , water stops running through water heater . If tankless heaters shut off burner when infeed water is too warm then I do not think I need a return water sensor . Otherwise , I might use sensor to switch solenoid to bypass heater and keep circulating pump running until room thermostat senses room is warm and then pump can stop .

I would only use anti freeze in a closed loop system that does not connect to my existing domestic plumbing in anyway . I would need a heat exchanger to transfer heat for my domestic taps if I want to change that sometime in the future . I do not drink my tap water anyway but I must consider that visitors might by mistake . It would also be ridicules expensive to lose anti freeze through taps . I want this anti freeze left in all the time for unexpected breakdowns or power failures . I live here all year round . Power failures can last for days when weather gets nasty . There is also a new problem developing concerning the North American power grid . The magnetic field of the planet protects us from solar radiation . Magnetic protection is week at the poles . Magnetic north pole is moving and when it gets to close to the distribution grid which is expected to happen in a matter of a few years ,the grid will be overloaded during solar storms . There is reason to believe that extended power failures will become very common . There is real science behind this . This might not be news people scaring us for ratings like the Y2K doomsday crap that never happened .