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 ?