Unusual electric heater

[davidaprice]

We’ve a small hot water tank in our boat, heated by the engine’s cooling water. We recently got round to connecting up its electric heating element, so we have (small amounts of) hot water when we’re on shore power. But we noticed a strange effect: a day after arriving, our engine was still hot to the touch. In fact, it was warming the boat quite nicely.

What seems to be happening is that the hot water in the tank is setting up a circulation in the engine’s cooling system, heating up the engine. Is this normal? Do people e.g. install taps on the cooling circuit to stop it happening?

 

[RichardS]

We’ve a small hot water tank in our boat, heated by the engine’s cooling water. We recently got round to connecting up its electric heating element, so we have (small amounts of) hot water when we’re on shore power. But we noticed a strange effect: a day after arriving, our engine was still hot to the touch. In fact, it was warming the boat quite nicely.

What seems to be happening is that the hot water in the tank is setting up a circulation in the engine’s cooling system, heating up the engine. Is this normal? Do people e.g. install taps on the cooling circuit to stop it happening?

What is normal would be to fit a non-return valve in such circumstances.

Richard

 

[Rafiki]

Your profile says you are in Finland - so surely in those cool autumns and springs this would be good. I appreciate that this week it has been very hot over there though.
Seriously though, I have never noticed a similiar effect in my own set up, so something must be wrong.

 

[davidaprice]

What is normal would be to fit a non-return valve in such circumstances.

But isn’t it possible that the induced circulation in the engine cooling water is flowing in the usual direction? There’s no easy way to check. Actually, it occurs to me that I don’t know how the usual circulation occurs, is there no pump?

 

[lw395]

A non return valve may have too much back pressure?
A lot of people never use the electric element.
Fitting a 1/4 turn valve in the circuit would be fine.

 

[Graham376]

What seems to be happening is that the hot water in the tank is setting up a circulation in the engine’s cooling system, heating up the engine. Is this normal? Do people e.g. install taps on the cooling circuit to stop it happening?

Quite normal with our boat. Why insert another valve to have to service and remember to turn on/off with engine use?

 

[RichardS]

But isn’t it possible that the induced circulation in the engine cooling water is flowing in the usual direction? There’s no easy way to check. Actually, it occurs to me that I don’t know how the usual circulation occurs, is there no pump?

As you say, the circulation in the engine cooling circuit is through conduction. The best way to stop this without installing a manual valve which the OP would have to remember to open and close, is to install a NRV or do some hose re-routing. He would need to check which way the conduction is operating but it would presumably be rising from the highest connection to the calorifier coil. A quick hand against the hoses will soon determine the flow direction. It might even be worth simply swapping over the two hoses to the coil as that might stop it.

It might also be possible to stop it by re-routing that hose so it heads downwards after leaving the calorifier but if re-routing or swapping the hoses over is not possible or doesn't solve it then an NRV to block the direction of conduction flow in the upper hose will certainly do the trick. If that happens to be also against the flow of water produced by the coolant circulating pump, then simply swap the hoses over anyway.

As someone says, apart from wasting some electricity which might an a concern if one is paying for it, I can't think of any reason why it would be damaging to the engine so if the leccy is free, it might be easier to leave it as it is.

Richard

 

[Leonidas]

There should be a shut off valve near the engine so you can isolate the cooling water branch to the calorifier. Calorifiers should also have inlet and outlet shut off valves.

 

[pvb]

As you say, the circulation in the engine cooling circuit is through conduction.

Not convection?

I'd try re-routing the pipes; putting in valves is a nonsense.

 

[RichardS]

Yes .... convection, but no sweat as it's not material.

Richard

 

[PowerSlapper]

We tend to "plug in" a few hours before departure to give a tank of hot water and "preheat" the donk which eases the load on the batteries and starter motor.. This also allows the fridge / freezer to chill down as well before we sail with out us having to motor sail or run the generator. As we don't leave shore power plugged in when we leave the boat the convection heating is not an issue (immersion usually off though in any event (force of habit)

 

[lw395]

Quite normal with our boat. Why insert another valve to have to service and remember to turn on/off with engine use?

Because heating the engine instead of just heating enough water for a quick shower takes a lot longer.
It might be possible to stop the issue happening by careful routing of the pipes?
The calorifier circuit should presumably only be open when the engine thermostat opens?
If the hot water from the cylinder coil has to go downhill to reach the thermostat, it may never open?

 

[vyv_cox]

Not an unusual occurrence if the engine is higher than the calorifier. As has been said, looping the hoses downwards will fix it. An NRV will also do it, I have one on my central heating system at home for exactly the same reason, but it may introduce complications in operation. I don't agree that calorifiers 'should' have shut off valves. They might be useful but I have never needed them with either direct or indirect heating.