Our 24M had Arctic pac heaters on the waste tanks but none on the fresh water tank.
The fresh tank had one heating duct from the furnace going to the area containing the fresh tank which would keep it from freezing only if the furnace was running. The furnace therefore was sending heated air to the outside and replacing it with cold air drawn into the living area. There was no thermostatic control of the heat supplied to the fresh tank.
I purchased a third heating pad for the fresh tank and installed it and connected it to the same circuit that operated the other two heaters for the waste tanks. I changed the fuse to that circuit to a larger one for the 50% increase in current. I also choked off the hot air supply duct from the furnace to the fresh tank.
The original setup seemed like a waste of propane and a risk of freezing the fresh water due to no automatic thermostat control. The only cost was the additional heating pad and my labor.
I think this should be a factory design change for all units if it has not been changed already.
On all the other floor plans the fresh water tank is installed under the bed area, so in conditioned space. On the 24M this would not fit, this the duct work.
As for no thermostatic control, as long as the furnace is working then you should be fine. This is how most Class A's do it and how we do it on all our gas Class C's. All you're trying to do is keep the fresh water tank above freezing. So if you're warm and toasty inside (or just warm) the tanks should be fine. The thing I don't like about the 12V pad heaters is when dry camping it drains batteries pretty quickly.
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We are in the process of ordering a new 24R and I'm pretty sure the fresh tank is not under the bed or in the heated living area. I'm requesting a heating pad on the fresh tank for that one. We are in Vermont where it might get below freezing when the motorhome is in the driveway and not winterized and I will use the furnace at a minimum setting to keep the plumbing from freezing, but I do not want to use propane to send heat outside through the fresh tank area wherever it is.
To access fresh water tank drain valve, open lift up panel behind left rear tire, see black door, open and the drain valve is to the bottom left of the tank. you can also see the tank behind the water pump
Turned the thermostat of my 2014 Solera to furnace. No heat inside, but the outside vent is blowing hot air. Looked over manuals, no info on furnace operation. What do I need to do to get hot air INSIDE?