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Old 18-04-2014, 13:51   #1
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heating hot water with engine

Does anyone know of a hot water heater 120v & 12v that will heat water with engine at idle and water temperature up to 150 F. Seaward says engine must be under load at least 45 min. to open thermostat and have water flow thru heat exchanger. Would like to have hot water while at anchor and charging batteries. Thanks for any help from anywhere.
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Old 18-04-2014, 14:15   #2
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Re: heating hot water with engine

None I know will heat with 12V. But there are lots that heat with engine heat and 120V. Nearly all chandleries sell the engine/120V dual heat variety.
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Old 18-04-2014, 14:21   #3
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Re: heating hot water with engine

It isn't the fault of the water heater manufacturer--all engine heat exchangers require the engine to be warmed up. Some water heaters are well insulated and may hold heat overnight.

A propane-fired instant water heater would do the job.
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Old 18-04-2014, 14:31   #4
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Re: heating hot water with engine

First of all, running your propulsion engine at anchor to charge batteries and heat water is not a good idea. Operating for a long time at low load is bad for the engine- carbon build up, glazing of cylinder walls, etc.

At the very least put the transmission in reverse gear (at anchor) and rev up to at least 1,200 rpm. That will put enough propeller load on the engine to heat it up to operating temperature (open the thermostat) in 10-15 minutes rather than 45 as Seaward says (and they are probably right).

Most high output alternators need at least 1,200 rpm anyway to put out decent amps. If you don't have a high output, externally regulated alternator get one. Otherwise you are pissing into the wind trying to charge batteries with the OEM alternator.

Once the engine starts heating up feel the hose going to your water heater. It should start to get hot and build temperature as the engine warm. It takes about 1 hour of running at these conditions to fully heat a hot water tank.

It doesn't matter whose hot water heater. All of the marine water heaters have the same hot water coil that can be plumbed to the engine and a 120V electric element. You can replace the 120V element with a 12V element if you want to heat water that way. Another way is with an inverter.

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Old 18-04-2014, 15:11   #5
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Re: heating hot water with engine

My Yanmar 3gm has a bypass on the thermostat that allows cooling till it opens. My water heater comes off that connection allowing it to heat the water.
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Old 18-04-2014, 15:35   #6
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Re: heating hot water with engine

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Originally Posted by sailor0516 View Post
Does anyone know of a hot water heater 120v & 12v that will heat water with engine at idle and water temperature up to 150 F. Seaward says engine must be under load at least 45 min. to open thermostat and have water flow thru heat exchanger. Would like to have hot water while at anchor and charging batteries. Thanks for any help from anywhere.
sailor0516
Alot depends on your engine temp. Some run real cool, newer ones hotter. I can tell you this, I had a standard Seward type on more than one boat. My main charging on 3 cruisers was the main engine and alternator. The water heater would get so hot it was too hot to use without having a cold tap mixer. If I ran the engine to charge noonish or late morning, the water would still be warm enough for a shower the next am.
(Yanmar, Mercedes/Nanni and Perkins fresh water cooled engines)
I wont argue the use of the main engine for charging, it's been discussed many times. It was the way it was done for many, many years, and keeps the cost of outfitting down significantly as well as a more seaworthy uncluttered boat exterior.
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Old 18-04-2014, 16:00   #7
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Re: heating hot water with engine

Get a solar bag. Quick, simple and inexpensive.
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Old 30-04-2014, 16:01   #8
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Re: heating hot water with engine

I have this system with a Sigmar water heater and heat exchange with a Volvo D2-55. It has recently failed : I can have hot water on shoreline but not with the engine.
Is the engine thermostat responsible of this failure, and would its replacement solve this problem ?
Thank you to those who had a similar experience.

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Old 30-04-2014, 16:11   #9
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Re: heating hot water with engine

The thermostat failing, open, would only slightly reduce the fresh water temperature, once the engine was mostly warmed up, which would take longer. It failing, closed, would result in the engine overheating.

It's more likely a blockage/fouling in the heat exchanger.
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Old 01-05-2014, 06:39   #10
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Re: heating hot water with engine

Just to elaborate on Terra Nova's comments... If your engine is warming up to normal operating temperature reasonably quickly, and then holding steady there, then it is not your engine thermostat that is the problem. And if your engine is NOT warming up to normal operating temperature reasonably quickly, and then holding steady there, then hot water is the least of your problems!
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Old 01-05-2014, 06:50   #11
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Re: heating hot water with engine

I was told by a major Volvo parts distributor that a thermostat can stop the flow of coolant to the water heater. He said the system works different than what we are accustomed to. He said if the thermostat stayed closed or either the thermostat or tube with small holes was installed backwards there could be no flow.

I have the same problem after replacing a stuck thermostat which caused high engine temps. I will check it out this week and report on what I find.

In trying to solve the problem I replaced the water heater and put leaders in the hoses to make sure it wasn't a sir lock problem. The hoses stay cold with the engine at 160 deg. The engine does not over heat.
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Old 01-05-2014, 07:45   #12
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Re: heating hot water with engine

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Originally Posted by djmarchand View Post
First of all, running your propulsion engine at anchor to charge batteries and heat water is not a good idea. Operating for a long time at low load is bad for the engine- carbon build up, glazing of cylinder walls, etc.

At the very least put the transmission in reverse gear (at anchor) and rev up to at least 1,200 rpm. That will put enough propeller load on the engine to heat it up to operating temperature (open the thermostat) in 10-15 minutes rather than 45 as Seaward says (and they are probably right).If you run your engine in reverse gear while on a mooring or at anchor, you will stretch out your mooring/anchor chain to its max length while all the other boats around you are more or less on top of theirs, and then your boat will paddlewheel around in a big circle while all the other boats are stationary. It will load up your engine and generate heat, but you need a LOT of room to do it without bumping into your neighbors boats.

Most high output alternators need at least 1,200 rpm anyway to put out decent amps. If you don't have a high output, externally regulated alternator get one. Otherwise you are pissing into the wind trying to charge batteries with the OEM alternator.

Once the engine starts heating up feel the hose going to your water heater. It should start to get hot and build temperature as the engine warm. It takes about 1 hour of running at these conditions to fully heat a hot water tank.

It doesn't matter whose hot water heater. All of the marine water heaters have the same hot water coil that can be plumbed to the engine and a 120V electric element. You can replace the 120V element with a 12V element if you want to heat water that way. Another way is with an inverter.I've never seen a 12V element for a hot water heater. How many amps does it draw and how long would it take? In order for his alternator to put out anywhere near the large amount of amps needed to heat water with DC power, he would have to run his engine well above idle so he'd once again be running his engine with low load with the same attendant problems as if he were trying to do it with the heat exchanger.

That would have to be one VERY large inverter and battery bank to heat up supply enough power for a typical hot water tank.

David
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Old 01-05-2014, 07:56   #13
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Re: heating hot water with engine

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Originally Posted by djmarchand View Post
First of all, running your propulsion engine at anchor to charge batteries and heat water is not a good idea. Operating for a long time at low load is bad for the engine- carbon build up, glazing of cylinder walls, etc.

At the very least put the transmission in reverse gear (at anchor) and rev up to at least 1,200 rpm.
Why do you think one has to be in gear? I run our engine, out of gear, at 1500 rpm and it heats up just fine. I rarely use it to make hot water, just to get a charge on the batteries if I'm going to be at anchor for more than a night (i.e., not motoring anywhere on day 2). The end result is I get a little, very little but some, hot water. M25 engine.

I'm happy my anchor is set and I wouldn't want to put that kind of load on it unnecessarily. I set my anchor properly with reverse engine when I drop it. My anchor is noted in my signature. While it may seem small for some, I have sized the anchoring system for 42 knots for my boat, I'm not out in any conditions even close to that.
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Old 01-05-2014, 08:01   #14
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Re: heating hot water with engine

I don't know if this has been done before or not but don't see why it couldn't. With swimming pools and in home heating water solar panels are pretty common. All they are is a sheet of glass/ plastic and black water tubing underneath. They can heat the water in the coils very hot very quickly just on pass through alone. Why not try and make a small 1ft by 2ft say solar water heater and tie it into the hot water tank. You'd have hot water all the time at anchor engine or not? That or look at a pool products catalog and see how small of ones they offer. They are all meant for external use and are mostly plastic and corrosion resistant ect. I've always wondered why this doesn't seem to be common practice?
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Old 01-05-2014, 08:15   #15
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Re: heating hot water with engine

That's a very good idea. I use a Sun Shower, just easier to handle.
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