Winter Use Tankless Water Heater

[Steamboat]

Does anyone have any experience with Tankless Water Heaters during the winter? I'm trying to find a unit that will function in below freezing temps (possibly 0 to -5 degrees). I see Girard's gen1 had what they call a Winter Use Device, essentially a solenoid tee that kicks on the heater when it is in danger of freezing, then turns it off. Are their newer models, or other manufacturers with similar functionality? Would it be possible to buy the WUD separately and wire it in to any heater? Thanks for you help!

 

[2TrakR]

Have tankless, do not have the winter "kit" option on it. Have not done longer term sub zero temps with it without having the water off to the heater so it would not freeze.
I would recommend against the tankless unit.