using an electric tankless water for heating small apt???

[Mike Row]

Has any one tried using an electric tankless water heater for heating ????

I have 1bd 600sqf unit the heat calculation calls for 25k btu, NO boiler is made below 50k, I have radiant pex in floor heating, so my temp can be set to 120-130.

I hear that electric tankless water heaters are designed to take cold water and bring it up to 120 or whatever your setting is max 140

but with radiant after awhile my return will be 110 and going back out 130 using very very few amps to heat those 20 degrees but how long will that last ?????

or are they capable of taking on hot water and heat it even more ???