12-48 volt cabin heaters & blanket

[DaveP]

I have been looking for ways to heat the cabin on my Albin 25 and came across a very interesting website with a number of 12 & 24 volt cabin heaters. Some plug into the cigarette lighter and others hook to the battery but I'd never seen this selection in any auto, boat, or RV catalogs. There is even a 12 volt electric blanket to keep you warm at night. Just go to the link http://www.sportsimportsltd.com/12volth ... GgodC3PunQ

[Mariner]

I would look very carefully at the amp draws and BTU outputs of those heaters. Due to the nature of DC electical systems, it is difficult to produce much heat from a 12 (or even 48) volt heater. A space heater capable of heating a space the size of a boat's cabin would typically need to draw around 1,000 watts. On an 120 volt AC system, this is a mere 8.3amps. But on a 12 volt DC system, this is 83.3 amps. Even high output alternators typically only put out 100-150 amps, and the wire size required for this type of draw is very large, and very expensive. Most cigarette lighter circuits are only capable of 10-15 amps (and this is assumes a marine installation in which larger gauge wire is commonly used).

Instead, my guess would be that these heaters produce much lower amounts of heat, in order to keep the amp draw to an acceptable amount, and the wirinng to a practical size. They are typically relegated to uses like de-frosting the windshields of trucks whose diesel engines take too long to heat up, and whose drivers are anxious to get moving.

More effective solutions for cabin heat are diesel or propane furnaces, or a direct heat-exchanger unit. Diesel and propane furnaces utilize fuel that is arleady stored on the boat in abundance, but are often expensive. Diesel is safer, and typically has a larger supply to draw from. Propane furnaces are generally less expensive and easier to install. These both have the advantage of working even when the engine is not running, meaning they will keep the cabin comfortable overnight. A direct heat-exchanger is by far the most efficient, in that it simply piggy-backs off the coolant system of the engine and uses heat that would otherwise be lost out the exhaust to heat the cabin. It works just like the heater in your car, and consumes no additional fuel, and is a relatively inexpensive installation. But unlike the furnaces, it won't work when the engine isn't running. In my opinion, a well equipped cruising boat will have both systems.

If you spend most of the time in marinas connected to shorepower, or run a generator constantly for other reasons (typical on commercial vessels), a couple good quality AC space heaters, or a reverse-cycle A/C system will be good alternatives.

[DaveP]

Thank you for all the information both pro & con of using a 12 volt cabin heating system. I'm sure you are exactly correct about the amp draw to run an adequate 12 volt heater. I'm leaning toward the heat exchanger and diesel heater that you suggested but it will be sometime next winter before I'll be able to afford to intall them. Thanks again.