Engine coolant to water heater

[bostonhatteras]

We have this feature on our Hat with Crusaders. The only problem is that after a long run the water is so hot that it trips the overtemp bimetal. If you don't realize that, the next day your hot water is cold as the electric element is not powered until you reset the mechanical button on the heater itself. On mine that button is under a cover'

This is an interesting comment in that the bimetal safety switch adds user complexity where I am attempting to make end user complexity less. I did read in the manual that there is a 'red reset button' and I questioned it for a second but then glossed over the whole idea thinking what would cause a need for reset in an electric heating element. There is no more in the raritan manual than pointing out in a diagram that there is a reset button. There is not any operating parameters given or reasons presented for a potential reset. Speaking of getting something for free, the cost of quality hose, clamps, valves etc to pipe this in would probably be a few hundred all told. If it takes two hours of electric operation to fully heat the water, then at 5 dollars per gallon I would have to not run the generator 30 times to break even. The convenience factor would outweigh the money spent but if I have to press a reset button deep in the engine room on a regular basis that would get old really fast. I think I need to contact raritan and find out what trips the 'red reset button'.

[Maynard Rupp]

The red button trips when the water is too hot. I wouldn't plumb it to the generator. It should T in to the coolant system on one of your main engines, usually the one closest to the hot water tank. If you are going to run the genny, it makes electricity and can power the electric element in the heater. It would make no sense to plumb coolant lines from that unit to the hot water heater.

[janice142]

Thank you fanfare... with the new engine going in shortly all these questions are coming to the surface. One less "thing" is always good. Besides, I can run off my solar regulator a hot water heater when the batts are full, so that sounds like the least onerous choice.

Timely thread.

[Canuck Dennis]

I know that DD will cancel warranty on any installation that does that...YMMV

[jim rosenthal]

All of the above are true: very hot water in the tank, added complexity, etc. But the sailboat and trawler crowd have been doing this for decades with very few problems if any. The savings in electric is not a factor- if there are even any savings at all. The convenience is well worth it. I don't run the genset while running the boat- all it would do is keep a (small) fridge cold and I don't need that. Having hot water when you get there, that stays hot for days, is very convenient.

Yes, some boats have the hot water loop tee'd off the genset. That works fine as well, and gensets are usually set up with a loop outlet (s) to do it. Depending on where the heater and genset are located, it may be a long hose run, which I don't care for.

As far as antifreeze getting into the water supply, I have not had that problem nor have I heard of anyone with it. Of course every possible problem will occur at some point on someone's boat, but there are a lot of sailboaters and trawlers in our area, and I asked one of the companies that does a lot of these installs, because this thread made me curious. They have never had a problem with an AF leak into the fresh water space of the water heater, either.

Commercial boats also use space heaters plumbed into the coolant loop to heat cabins and work spaces in boats- the heaters are sold by Hamilton Marine. These also work very well. They also use coolant loops to heat the water heaters on some boats, which is interesting because their gensets run 24/7. It may reduce fuel use in the genset enough on a boat with a crew and continuous operation that it's worth doing in that situation.

[Genesis]

Heat rejected to the cooling system is of course energy you paid for (in fuel) that is wasted. If you use that energy to heat water then you are getting useful work from it, and that is a net win, particularly when it comes with convenience you didn't have before as well.

[Boatnut]

Up north in the old days, our boat was plummed to circulate the engine hot water through hot water heater units to keep the boat warm while fishing in the late fall days. It was also plumbed for the engine to heat the hot water as well. Used these systems for 20 years or more, never had any problems.

[jim rosenthal]

Yes, I think those are the radiators that Hamilton sells. I think I am glad I live in a climate where I don't need them. They would be great in NE or the PacNW, though. Or if you used your boat year-round in these parts.

[SKYCHENEY]

The engine heat option is very common in large motorcoaches. Look up the Aquahot system. They use a Webasto diesel fired boiler to provide domestic hot water, engine pre-heat, and radiant heat inside the coach. When the engine is running, the coolant from the engine does the heating and the boiler does not run.

I designed a similar system on an old Eagle bus that we converted to a motorhome. It worked great, but as was stated earlier, I'm not sure I would feel comfortable having coolant lines running all over the boat. A motorhome is a totally different animal.

[Mike36c]

I had this set up on a Tiara years ago and as mentioned above that water is HOT, dangerous hot in my opinion. Haven't had it since and don't miss it. Not only is the shower hazardous, the faucet is too. I wonder if a thermostat arrangement could be fabricated and engine recirc water automatically cut off once above a certain temp, that would be the ticket.