Engine coolant to water heater

[bostonhatteras]

On my new water heater which is a raritan 20 gallon, I have the ability to heat the potable water with hot coolant from the engine. I know everybody understands the concept and has probably seen this personally. What I don't know is where to tap off of the engine. The engines are 8v71 and at the bottom rear of the water jacketed exhaust manifold is one place where coolant could be tapped. From there I need to find a place in the coolant circuit that will actually flow water through the potable water heater and not simply pressurize the thing with static coolant. There must be preferred ports on the engine to accomplish this. Another question I have is whether it is actually worth the effort to do this? I'm thinking it is but maybe I'm looking through rose colored glasses. Any advice would be greatly appreciated. Thanks. Russell.

[SKYCHENEY]

I don't know where to tap, but we did have a boat with this feature. It was very nice to have hot water without running the generator. I would do it again if the option was available. It shouldn't cost much to hook it up.

[jim rosenthal]

I have this on my Hatteras, and if the engines were Cummins I could tell you where to hook up, but on DDs I don't know. Your best bet would be to try Boatdiesel.com, I think.

I would not have a boat without this feature. Not having to run the generator to get hot water (and it is HOT! watch out!) is a huge convenience. Like when you've run the boat all day, and you dock and wash it down, and you want a hot shower. It's brilliant.

On my boat the water heater is in the engine room, which tends to stay warm for a day or so after the boat is run in mild or warm weather. So the water in the water heater stays hot longer as well.

When you do the installation, be sure to put ball valves in the water lines to the heater from the coolant jacket. There are times when it may be useful to be able to turn the water heater coolant loop OFF.

Keep in mind (see above) that the engine coolant will heat the water in the water heater tank to engine temp. If your engine runs at 195F, your hot water will be at the same temp. A little of that goes a long way, so don't step into the shower with the hot water on full unless you are made of asbestos or stainless steel yourself. And set the water flow and temp up before you let a kid get in the shower.

Incidentally all sailboats and trawlers are set up this way.

[bostonhatteras]

I have a couple solutions figured out. Referring back to the coolant hose that connects the rear lower cylinder block outlet to the exhaust manifold port, this is where the connection should be made as far as I can tell now. I have two methods for using this hose/port area. The first, with two main components, is to thread on two 5 port valves with two of the ports blocked (two per valve). This allows two handles to control everything. caveat is that the largest 5 port valve is 3/4'' and the existing hose on the engine is at least 1''. The water heater ports are 3/4'' though. Second option is three regular ball valves and two tees. This would have the hose running between lower block and exhaust manifold replaced by an assembly of hose to tee to hose to ballvalve to hose to tee to hose ( could get threaded parts but then need to thread on hose barbs additionally). in this scenario the tees would shunt water off to the water heater once the ball valve was closed. two additional ball valves would go into the lines to and from the water heater. This second scenario requires three valves to be turned. The two ball valves on water heater feed lines could be omitted but then the water heater cant be isolated, same for the first scenario needing two 5 port valves to isolate the water heater. Both of these solutions leave something to be desired though. I just went on boatdiesel and the pdf library is messed up. it flashes, or continually reloads the pdf youre trying to view so I guess Im waiting until I get back to the boat and Ill look at the manual there for cooling system flow diagram. finding two unused ports and using two ball valves would be ideal.

[jim rosenthal]

That is what we did and it worked fine. Email boatdiesel and see what they say. Are you a member? I think you need to be in order to see some of their tech stuff.

[Fanfare]

As energy costs rise it is always nice to tap into "free" solutions such as using engine heat to warm our hot water. On my boat the water heater is probably the second highest user of electricity next to the stove. But just as in the oft-cited "free lunch" you should be aware of possible downsides to this arrangement.

By tapping into your engine coolant you add complexity to a sealed system. The extra piping to the water heater is more vulnerable to breakage than the DD design which is mostly cast iron and quite sturdy hose connections. Since the worst thing one can do to a DD is overheat it (especially the '92 series, which ruins its o-ring seals) this should be approached carefully.

Depending on the antifreeze you use the solution circulating in your engine may be toxic. You probably cannot easily examine the inside of your hot water tank to check for leakage in this internal pipe. I don't use my hot tap water for drinking because I have seen the grunge inside my water heater when changing its elements. But others might. Coolant overflow kills many pets when they lick it up from beneath cars. I don't know how much antifreeze it takes to kill a human, but it may not be much. You don't want this to happen on board!

My engine coolant stays steady at 175 degrees. Consumer Reports recommends that water heaters be set between 120 and 140 degrees for sanitizing with a dishwasher. 175 can give a serious scald. And my boat does not have the modern equalizing shower valves that prevent sudden temperature shifts when other faucets are turned on or off. I keep my water heater at 120 because my grandchildren are aboard. But also I have a huge replacement water heater--it balances my port list, and my rather odd 1965 dishwasher was long ago removed. My heater has 4-5 inches of foam insulation around it and stays hot enough for several days in southern climes. My generator is sure to be on for part of this time ensuring my supply of hot water. My heater has two 1,750 watt elements and I have added a switch to keep the top element off unless needed. My boat also came with a lighted switch in the galley to turn the hot water heater off when I need to reduce my electrical load, probably because my boat came with 30 amp shore service which in the old days I often exceeded.

Should I want to use heat, I would probably tee off the generator rather than the main engines. My generator runs far more hours than the mains. Maybe non-toxic antifreeze could be used in it. It won't need as much antifreeze as the big engines, which have rather specific requirements for coolant. The generator engine is cheaper to replace than a DD and best of all it has an automatic overheat switch should there be a break somewhere in its cooling system.

Because of these reasons I decided to forgo using engine heat in my water heater. While it would likely save me a bit on generator fuel the amount would probably be lost in the rounding considering my normal generator use. For me the cost, complexity and the hazard just doesn't add up. But your mileage may vary.

[rsmith]

What Fanfare said! KISS

[SeaEric]

What Fanfare said! KISS

+1. Thanks Jim for a very thoughtful analysis and reply.

[Maynard Rupp]

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'

[Boatsb]

My water tank in down the center of the er. I get 150 gal of 120 degree water after running for the day. The water heater is only needed when we dont run. No need for all the extra plumbing.