Achilles Heel: Heated Tanks but not Water Lines

[steve2777]

On my 2018 Siesta 24ST, on this winter's Southwestern trip, I discovered a significant flaw in its cold - weather water protection. On two mornings when boondocking, with overnight temperatures hitting mid or low 20's, the next morning I had no water from any hot or cold faucet. As the morning temperature rose, the water began to flow again, and there was no apparent permanent damage. The Siesta is equipped with "enclosed heated tanks", and unlike the electric pads used in other rv's, Thor achieves this by piping a small duct from the furnace through the bathroom, forward to the location of the black and grey tanks. This pumps furnace heat across the top of those tanks. (The fresh water tank is already above the floor, beneath a bunk, so protected.) While I don't know how effective hot air across the top of the tanks, when the liquid is in the bottom, will be, that is not where the problem turned out to be.

Thor runs the water line from the water pump down through the floor, to the cold outdoors, then right angled into the basement compartment which contains the metal box where the city/fill/normal selector switch is located. All water must pass out to this selector, then back in to the coach. There is no heating in this compartment or box, and the water lines to and from are completely exposed to the elements.

As for the exposed water lines, I'm planning to build up a heavy layer of spray foam around them. I'm debating whether they should be also first wrapped with heat tape. Also, the unheated selector switch / box seems like it's going to need to be addressed as well, though I haven't tried to see if the box face can be removed to get to the inside. There again, I'm debating whether to use just spray foam, or also heat tape.

Has anyone else been through this problem yet? What was your approach and results? Thanks.

[MJC62]

As a retired 35 year member off Heat & Frost Insulators Local 17. I will give you my professional opinion. I advise against spray foam on anything that may ever need to be repaired or replaced. For obvious reasons if it is properly installed on a clean surface it is a nightmare to get off.
If you plan to insulate the lines use a low temperature heat tape and run the strip along the bottom of the line it is not necessary to spiral the tracer on a line you intend to insulate. Attach the tracer with strapping tape.
Next is the piping out of the weather? If yes than after applying the tracer, at the local hardware get a roll of the Fiberglass pipe wrap insulation, Frost King makes it, then spiral wrap the lines with the glass. Use your trusty duct tape to secure it.
If the lines are out in the weather where they might get wet. You are better served to insulate them with closed cell foam insulation. You will need to oversize the pipe insulation to cover the pipe and take in the tracer. My guess 1/2 pipe covering should be plenty. You can also get the closed cell foam at the hardware.

[steve2777]

MJC62: Thanks, sounds like the way to go. Enclosed is a picture of the lines from floor to/from the basement locker: looks like Thor foamed into the entry and exit holes, but left the lines themselves completely exposed. I have no idea how far into the locker switch cabinet the foam extends, but my guess is if they didn't foam the lines themselves, there's probably no insulation inside the selector switch cabinet. Has anyone tried removing the front of that cabinet to get inside?

[MJC62]

Try wrapping the lines with the glass before you worry about a tracer. There doesn’t seem to be much exposed piping in that pic. The insulation will keep that small amount of ppg at its ambient temperature. If it continues to freeze you can pull the glass off and add the tracer later.

[steve2777]

MJC62: Thanks!

[Hooligan2]

My 24 ST, The ducted heat to the holding tanks has worked well down into the lower teens. However, when temps are going into the lower 20's, I put a 100 watt rugged bulb and aluminum reflector in the water compartment just in front of that metal panel. I plug into the pedestal.

If you boondock often it may be worthwhile to duct heat into that area also. The furnace has duct openings that are not used..

[steve2777]

Hoologan2: That's a good idea, Thanks !