Electrically there isn't much difference between a house and marine electric
only water heater. In a house the ground is connected via the water pipes, so you have to make sure you connect the boat ground likewise or whichever the appropriate place is in the manual. Electric
house water heaters are typically vastly cheaper. There may be something about the valve not working at certain angles,. But from what I've seen they're the same valve from the same supplier. Possibly swap out for the marine version and be money
ahead if this is the case.
Propane/Nat gas tank water heaters including RV propane
water heaters shouldn't be used. It's dangerous. Boats move more, sail boats heel specifically. Insurance
is unlikely to support it.
A marine specific water heater or calorifier
(outside us term) is different in a few important aspects. First the obvious is you can connect to the engine
and heat the water with engine
heat. This lets you disconnect from the dock
. You get a lot of heat from the engine. the hot water from my 7 gallon will burn me after 30 min run at load, which was about what it took to go into the marina. You will also find some of the new marine water heaters that have a combo 120v and 12v element, so you can heat from the DC bus or use as a dump load for solar
. As an alternative instead of connecting to the engine you can connect to a diesel
hydronics heater for heating
water anytime you want. For extra cost you can get some marine water heaters with 2 heater coils inside, 1 for engine, and 1 for hydronics or generator
. House water heaters have no need for either of those functions. Lastly The materials for a marine water heater are usually more corrosion
resistance. Stainless hardware
fittings ect. Tanks
tend to be thicker as well because the engine or dc element are not generally temp controlled. That means they build up more heat and pressure than a house or electric only marine water heater. Some marine water heater tanks
are made of steel
or glass lined steel
. Not sure if those are the cheaper ones or not, the one on my boat is made from stainless.
I've noticed that UK or european marine calorifiers may be much better than US marine water heaters. It appears they have better insulation
tanks, easy to get with one or two exchanger coils, can install higher pressure valves, have more dual 120v/12v elements built in, and come in a better range of smaller sizes. I was looking into a smaller 2-3gal with engine coil to install for the shower
as a heat exchanger
connected to a hydronic system. Couldn't find such an appropriate beast in the US.