hot water recirculation?

agesilaus wrote:
Why not use heat tape?

It would work fine as long as you are on shore power and they have a temperature switch that only energizes the tape when the temp drops below freezing. No plumbing and no pump.

The tubing in question is inaccessible. It is in a section of the underbelly which is covered by the black tank. I'm not willing to drop the black tank to get at the tubing. There is no access from inside the cabin.

DutchmenSport wrote:
That would work for you hot water lines. But what about the cold water lines?

Hopefully the warm water returning to the HWT via the cold water line will keep that line from freezing.

pianotuna wrote:
I think a mechanical thermostat might be more reliable.

Any chance of enclosing the waste tank area and then using forced air heating? That is what I use (but my tanks are already enclosed).

If I had planned further ahead, maybe some manner of framing could be built to enclose the tanks, and either light bulbs or a small heater could heat the entire area. My trailer is very very (very) low slung, there's only a few inches ground clearance, I'm not sure there's enough room to enclose the tanks without raising them into the underbelly first.

Right now I have 130 watts of heat pads on the gray (35g) and 65 watts on the black (20g) but the tanks are completely exposed to the elements. The exposed drain plumbing is wrapped with heat tape, reflectix and gorilla tape.

lawrosa wrote:
Im a plumber 30 years..

Get a watts check valve they use with thier recirc pumps. It uses the cold water as the return line..

...
Its a thermostatic check valve. When temp hits 95 F is closed. It continually opens and closes.

I would run the pump 24/7 when below freezing

I'll check that out. Maybe there's a lower temperature available? 95 F would be wasting a lot of energy, I'd think - maybe not?

RoyB wrote:
Check with SMKETNER on here on his HYDRONIC HOT WATER setup to keep his RV Tanks from freezing...

I have played with this concept using the RV Water Heater to heat up my trailer using a heat exchanger... Works pretty good when I tested it. Have not installed it yet...

I got this idea from another RV guy would installed it is his small floorplan trailer and it worked great fro him...

Very neat - I think I saw those diagrams before. What are you using for a radiator? My main concern was potability of the radiator's construction.

There are small copper core radiators for PC cooling, designed to handle 100-300 watts of heat. They have to meet ROHS requirements, which I think would make them drinking water safe as well.

I might be able to adapt this idea to add some extra heat to the tiny bathroom, without having to use a 120v fan heater in there.