Hot Water Heater Exchanger

After way too many failures in marine hot water heaters (powered by A/C and heat exchanged from an engine), I have decided to replace my last lemon with an A/C only unit. That leaves the question of what to do with the leftover plumbing from my port FL 120 that carried engine heated coolant to the old water heater. The outgoing and return hoses connected to the engine each have ball valves on them. I'd like to leave it all in place in case of future need. Is it OK to just shut these ball valves without causing problems in the engine cooling circuit?

Should be just fine- it's just a simple loop that feeds the water heater. Close the valves and think no more of it.

I can only guess but it seems that's what they are there for.....

Greetings,
Mr. PH. OK, it's a loop. Water goes out of the engine, through the heater and back into the engine. It doesn't go in and out at the same point so....the water must go out of one "chamber" and go back in another. If these exit and entry "chambers are not connected except by the water heater loop are you not starving the entry chamber by disconnecting it from the exit chamber? Not trying to be argumentative at all.

RT Firefly said:

Greetings,
Mr. PH. OK, it's a loop. Water goes out of the engine, through the heater and back into the engine. It doesn't go in and out at the same point so....the water must go out of one "chamber" and go back in another. If these exit and entry "chambers are not connected except by the water heater loop are you not starving the entry chamber by disconnecting it from the exit chamber? Not trying to be argumentative at all.

Click to expand...

Good question. Normally, heaters that tap off the engine cooling system are fed from dedicated connection points on the engine that are usually plugged (a screw port on the thermostat housing is an example). The ports are auxiliary, and capping them or closing the valves (as in this case) will have no effect on the engine- unless one leaks.

Implied in the proposal to shut the ball valves is to cap them as well. Just an added protection against a leak.

IF you use the boat in cool weather , there is your hook up for a box heater.

I have seen on older boats a small flat coil with a flip up cover.

Hot soup, coffee or tea , in the wheelhouse with no effort for the cook.

OR pipe it to towel heaters in the wet locker to dry out the foul weather gear.

Depends on how your system is piped up. On my Volvo the entire flow goes through the hot water heater so I hooked up a bypass line with an isolation valve. This gives me the option of flowing through the heater or not. I sometimes bypass the heater if running a higher rpm to get better engine cooling.

The Lehmans may only use a % of the coolant flow for h/w heating. No bypass would be necessary if that is the case.
If so, just close the valves and disconnect the hoses, but Definitely remove the hose fittings and install hex plugs, just in case a valve handle gets knocked to the open position accidentally, as Marty said.

I don't understand why you're having "way too many failures in marine hot water heaters". What sort of failures? Have you attempted to determine why you're having these failures?

In my opinion, eliminating the heat exchanger feature is in effect "downgrading" your boat. In my case, we rely on the heat exchanger to provide hot water after a day of cruising if we are spending the night anchored. No heat exchanger, no shower and no hot water for dishwashing.

As for dealing with the removal of the heat exchanger circuit, you can probably just close the valves, but not knowing your particular engine's cooling circuit, the safest way would be to make a loop with a piece of hose (you already have it) from the outlet to the inlet. Or just remove the hoses from the water heater and couple them together.

Captain K said:

After way too many failures in marine hot water heaters (powered by A/C and heat exchanged from an engine), I have decided to replace my last lemon with an A/C only unit. That leaves the question of what to do with the leftover plumbing from my port FL 120 that carried engine heated coolant to the old water heater. The outgoing and return hoses connected to the engine each have ball valves on them. I'd like to leave it all in place in case of future need. Is it OK to just shut these ball valves without causing problems in the engine cooling circuit?

Click to expand...

Show a pic/accurately describe where the takeoffs are and maybe we can help.

Mine comes out the bottom of the block near the oil pressure sender and a "T" in one of the big hoses that goes through the fan belt.

Those are definitely just a loop and can be shut off and not affect engine cooling...but the "T" fitting can't really be plugged so a new hose would be in order or just live with the ball valve and wire tie or remove the handle.

Heat exchanger failures are more likely to be a grounding problem at the dockside .

Depending on how the boat is wired , simply shutting off the HW heater will not stop the problem.

An isolation transformer will.

FF said:

Heat exchanger failures are more likely to be a grounding problem at the dockside . Depending on how the boat is wired , simply shutting off the HW heater will not stop the problem. An isolation transformer will.

Click to expand...

Ah, yes we have one. It's big heavy and makes a lot of heat. But it's definitely good to have, as I believe power back feeding lowers the life of your zincs.

Captain K said:

After way too many failures in marine hot water heaters (powered by A/C and heat exchanged from an engine),

Click to expand...

As others have asked, what failed?

If your hot water loop is creating stray currents and rotting out your heater, just think about the same effects working on the inside your engine. If not stray currents maybe old corrosive coolant?

BTW, per chance are your defunct hot water tanks made of Al? Or was your tank anode not changed out every few years? Eliminating the coolant heater core will not cure latent issues.

The most common cause of water heater failure is improper installation. Most are mounted directly on a deck and do not have hoses from the pressure relief valve or drain running to the bilge. Most are aluminum tanks wrapped in fiberglass batting inside a metal box. That batting will soak up every drip and corrode the aluminum tank.

Raising the tank by 1/2" by putting little blocks under the mounting flanges and adding hoses to the drain tap and pressure relief valve will greatly extend the life of the unit.