"Neil" wrote in message
...

"Larry" wrote in message
...
"Neil" wrote in :

Heater is a 12v 100watt ceramic heater

Make a little test before going farther down this slippery slope.....

Put a 100W lamp in the boat at dusk. Measure the temperature when you
start. Come back in the morning and see how hot it is inside the boat
from
this 100 watt heat source. I doubt it will raise the boat 1 degree.
That
will make it 11F inside when it's 10F outside....unless the wind is
blowing
through any hatches not hermetically sealed.

If you can't try this on the boat, try it in your garage WITHOUT parking
the warm car in there. Set a 100W lamp on the center of the floor at
dark
and check it in the morning. The boat isn't insulated like the garage,
either.

--
Larry

The ceramic heater is not a lamp, it will in 15 minutes defrost all the
glass in a Mercedes Estate car and raise the interior temperature to
acceptable before starting. Trying to source an appropriate thermostat to
operate it in the boat's water tank compartment.

Neil

Granted your ceramic heater puts out more heat than a 100 watt light bulb I
still think Larry has a point. You'd never warm up a whole boat with this
but I guess you might raise the temp above freezing in a smaller
compartment. How often is it going to cycle on though? Might end up
running almost continuously. A real nuisance as you don't have AC to
recharge your batteries.
Why don't you just pump out the water tanks, add some RV-type antifreeze
(pink stuff, propylene glycol) and pump that through the system. Now you
don't have to worry as much about the charge of your batteries, about high
currents periodically running through wires or the whole system failing and
the water freezing.