Certainly agree with everything you have stated
There a few Thor owners that have Aquahot heating and for those it is never a good idea to use air only
Given there are different series of hydronic heaters in various coaches which have different sizes of heating coils
The typical unit has around 160 feet of 1/2 inch tubing
Every spring there a few that tried air and then spend from 4000 to 8000 dollars due to the split copper tubing
Once through heaters or bypassed tanks air does work but you have to be very careful
Originally Posted by Judge
I'm on my second coach with the Girard Tankless water heater. The design could be much different than the AquaHot but I only used air on my last coach with it and never had an issue with damage from freezing. Last season I did run antifreeze through my current Girard unit.
Bursting of copper typically only occurs when a pipe / tubing is full of water such that when the water expands from freezing, it has no where to go and causes the pipe to burst.
If there is some residual water but plenty of air above it such that the water can expand and fill the void when it freezes, it should not damage the copper pipe / tubing.
As long as the hot water is open on each faucet when under air pressure, it should push enough water through the hot water unit so there is more air than water in the tubing and prevent any bursting.