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Mod #40: Holding Tank Heaters

Posted By Mark Corgan On July 17, 2008 @ 6:36 am In featured, heating | 18 Comments

There is so much to see and do during the winter season and enjoying these activities from the comfort of your RV can be a refreshing experience. But it doesn’t have to be winter in order for the temperature to fall below freezing. If you camp at high altitudes, even during the summer months, it is possible for the temperature to approach the holding tank freezing mark. By doing this mod, you can be assured that your holding tanks won’t freeze in all but the most extreme cold weather.

Mod Difficulty:

RV plumbing systems are pretty much the same in almost every RV. They consist of a pump, some plastic PEX (cross-linked polyethylene - you can use that one at your next party!) tubing, faucets, a water heater tank, and fresh, gray, and black water tanks. Some RVs have the holding tanks inside the RV while others are mounted below the floor, exposed to the elements. Although some manufacturers claim that their RVs have “enclosed and heated” holding tanks, that may be only partly true.

Enclosed typically means a thin piece of plastic sheeting called Coroplast that is screwed to the bottom of the frame rails running the length of the RV, covering the holding tanks. There may or may not be insulation in between the the sheeting and the flooring. Heated usually means that there is a small duct from the furnace placed through the floor in to the enclosed space for heating the holding tanks. In combination, the sheeting, insulation, and heater duct can help in temperatures down to about 25° F, that is as long as the furnace is running. When it’s that cold, most RVers use supplementary electric or catalytic heaters to save propane, which make the furnace run less, contributing to less heat supplied to the holding tanks.

OK, now that you know everything there is to know about the basic way holding tanks can be heated, let’s get on with the mod. To handle temperatures below freezing without having to resort to running the furnace full time, you can affix thermostatically-controlled heating pads specifically made for plastic holding tanks. These pads have an adhesive backing that is used to stick the pad to the holding tank. Simply peel and stick, after cleaning the bottom of the tanks of course.

You have three options for powering the heating pads: 120 VAC, 12 VDC, or a combination of both. If you have a huge battery bank then go with the 12-volt option. The 12-volt option can draw a lot of juice so plan your tank heating time accordingly so you don’t wake up to a tanksicle. If you know you will always have a 120 VAC electrical source, then go with the 120-volt option. These don’t draw nearly the current as their DC counterparts and are a good solution if you are a full-hookup kind of camper. To cover all your bases, choose the combination model.

You also have options for the size tank you need to heat. The larger the tank, the larger the heating pad, and the larger the current draw. And while some may think it’s only necessary to heat the fresh water tank(s), it’s imperative that you consider the black and the gray tanks as well. Damage from freezing can just as easily occur with the gray and black tanks if left unheated in prolonged freezing temperatures, let alone not being able to drain your tanks if they are solid ice (or whatever is in there).

Wiring is straightforward. For the AC model, simply plug in the heating pad cord in to an AC outlet. The DC and AC/DC combination pads require that you dedicate a circuit in the RVs 12-volt panel. There are usually enough spare circuits available in the RV power center to accommodate multiple heating pads. Simply run a minimum of 14 gauge wire from the pad to the panel, giving careful consideration to the polarity of the wiring: red to red (+ to +) and white to white (- to -). These are the most common wire colors for most heating pads. Don’t forget to place a switch between the positive wire from the pad and the power center. You need a way to turn the pads off! Any single-pole-single-throw (SPST) switch rated for at least 15 amps DC will do.

TipExamine your RVs plumbing to determine what measures may be needed to prevent damage from freezing temperatures. Some RVs have plumbing exposed to the outside elements. In this case, you should wrap the exposed plumbing with heat tape and foam pipe insulation.

TipIf possible, empty the holding tanks if they will be subject to freezing and pour a couple of quarts of non-toxic, biodegradable antifreeze into each holding tank (except the fresh!). This will protect the dump valves. Pour in more antifreeze as waste water fills the tanks.

ModMyRV recommends these parts for this mod:

General Reference
How to Cold Weather Camp in Your RV
UltraHeat RV Holding Tank Heaters


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