Domestic Hot Water from Engine Coolent

Our hot water heater*heats off of 110 vac or engine coolant. I don't know how common this setup is.

Does anyone worry that a loss of coolant due to a leak in the hoses to the heater or the heater itself will cause an engine overheat?

Do you have shutoff valves between the engine and heater? If so does the coolant have to bypass the heater and return to the engine or can just the heater intake be shut?

Thanks- Bill

Bill, Almost every boat I know of has this set up including ours. I have never seen a failure in this system, although like any other, leaks can occur. I highly recommend you DO NOT put a shut off in line. Forgetting to open these valves one time will make you regret it. In addition, valves will add more connections to leak. See our post here on our replacement and hose upgrades. Chuck

There have been a couple of times where I have needed to service the hot water tank (removal/repairs/rewiring, etc.) where isolation valves in the coolant lines saved having to mess with*coolant in the main engine.* This may be installation dependent.

In a coolant bypass installation, if one of these valves is closed,*coolant is simply not provided to the hot water tank.

When I repowered my old Mainship I put shut offs on both hoses going to the water heater. I tie wrapped them in the open position so they would not vibrate closed.* The water heater was 12 feet away from the engine so I used*150 psi *hose. Very thick wall and the price was right.

My current boat with the Lehman is a very short run. There are no shut-offs. I just changed out the water heater last weekend and lost so little antifreeze it wasn't worth worrying about.

"How many times have you heard of a heater hose leaking?"

Actually fairly common place here in the northeast. Perhaps it's the temp changes that affects the hose. Regardless, it's something to consider for sure.




-- Edited by jleonard on Friday 10th of June 2011 01:13:06 PM

Thanks everyone for your replies.

I am still not sure if the hot water heater is in series with the other heat exchangers. If a valve was installed and shut would it stop all coolent from flowing throught the motor, not a good thing I'm sure.

I will probably replace the hose runs(eleven years old) with good wire reinforced hose, without valves.

DavidM wrote:
Millenium:

I am absolutely certain that the water heater circuit is in parallel with the main engine coolant circuit.

When I bought my Mainship 34T five years ago the water heater was not connected to my Yanmar 6LY. I asked on boatdiesel and they gave me a diagram as to where to find the fittings. I removed two PLUGS and replaced them with elbows and barbs for the heater hose. One plug is on the coolant circulating pump and is at higher pressure. The other one is downstream at a lower pressure point.

The engine now circulates hot coolant through both systems in parallel.

David

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*am i right thinking that the domestic water will only start circulating when the engine reaches operating temparature the temp controlled valve will open to commence circulation of coolant into the engine block?

boatk9 wrote:
I have a nagging concern that antifreeze will get into the potable water supply.

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*lol thats poison btw

heard its sweet tasting so be on the lookout for that

Bill: Your boat must be in fabulous condition, as you don't have anything to worry about and have time to dream up these "worries".

My original engines had the 1/4 turn shutoff for the domestic lines, at the engine. My repower has them on both engines, so I got to choose which to use. All flawless since new (1980 boat, still with original HW domestic system, 1990 engines repower, installed in 2000).

boatk9 wrote:


I have a nagging concern that antifreeze will get into the potable water supply.

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I have this fear also. In residential hydronic heating it is not allowed to used ethyl glycol in a system that has a indirect (heat exchanger) hot water heater, propylene glycol is what is required by codes.

I haven't heard of anyone getting sick either. I have been asking Hurricane combi heater salespeople the same question, and I get blank stares.

I am not sure what route we are going to take, but it seems odd that it is acceptable in boats but not in our homes.

"I have a nagging concern that antifreeze will get into the potable water supply."

Correct ,it could happen, in homes they use require double wall tubing inside the HW tank when solar heating.

Boat heaters have no such rules , however if you worry the engine can be operated on CAMCO or similar non poisonous anti freeze.

Residential as I said requires food grade polpropylene glycol.* I don't know if it is adequate or good idea for a marine engine.

There are now non poisonous anti freeze for engines.

Google and a bunch come up, here is one,

http://www.amsoil.com/storefront/ant.aspx

Nice looking boat there, FF. If it has a tabernacle it must be just about perfect.

My 3 cents:* I learned long ago, due to fungi circumstances that can occur inside old, secluded freshwater tanks, to NOT use "house water" for cooking or drinking.* That said... there are plenty who do, especially with high grade filter systems.* I still play in category of old world safety technique.**IMO Washing dishes, shower, etc*is fine from boat tanks.* For drinking and cooking water*we use multi gallon clear plastic*carry-ons that we regularly clean-out with dish detergent.* Or, bottled water just for drinking. - Art

I have a Californian 34LRC with Detroit 8.2 engines. The PO experienced a destructive overheat on the port engine due to a clog in the hoses supplying heat to the hot water system. The answer was a simple bypass consisting of a pipe going across the hoses leading to & from the hot water heater. One hose comes from the engine oil cooler to the heater, the other goes from the heater to the fresh water pump. Frankly, I had not given much thought to the issue of contamination prior to this discussion. I have never had any problem during heater maintenance or replacement with fluid loss, etc. My concern is that there may be some disruption of the cooling stream, as that engine seems to have a higher oil temp than than the other side. Working on it.

chc wrote:
The PO experienced a destructive overheat on the port engine due to a clog in the hoses supplying heat to the hot water system.

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*So what is different about the stardboard engine plumbing that not having a water heater connected is different than having one with no flow through it?

Nice looking boat there, FF. If it has a tabernacle it must be just about perfect.


It does, was wondering if anyone ever looked at the pictures , so took down the lobster cruiser and put up the 90/90, for a change.

Rick;
I do not know the circumstances that led to the overheat; it may have been an internal issue in the heater, or failure in the hose run (12' out & back) to & from the heater. It happened, leading to a new engine on that side. Normal hose run is a single 6" hose from the oil cooler outlet to the fresh water pump. Apparently there was no bypass provision installed at that time.
When it clogged, flow stopped. A reminder to check/replace hoses periodically? Just in case.