Calorifier loses heat too quickly.

[Piddy]

I have a new-ish 40 litre calorifier under my cockpit locker floor which is heated either by running the engine or using mains. Both work well and produce lots of hot water.

However when not attached to mains, even if the hot water isn't used the water temperature drops dramatically overnight to a point where it's no use for anything.
What I noticed for the first time this last weekend (whilst plugged in) is that the hot water is keeping the engine hot 24hrs after the engine was run it was noticeably hot to the touch. No problem when plugged in but I suspect it's somehow transferring the heat from the caloriifer to the engine through the coolant pipes that connect the two.

This isn't the case on other boats (I have friends that have enough hot water to shower the next day).

Is there a valve I should have fitted or should the pipes follow a particular route to/from the engine to the calorifier. I have found internet sites that mention thermal loss but I wonder if anyone has had any success at this? I do have a non return valve to stop cold water entering the hot outlet pipe but that's it.

Thanks in advance.... Mrs Piddy will be delighted if I can fix this one....

 

[NormanS]

I'm no expert, but it sounds as if you need a non-return valve on the appropriate side, between the engine and the calorifier.

 

[sarabande]

for a start, is the calorifier located above or below the engine block ? If below, then you may have a thermo-syphon loop which is the cause of the heat going back to the negineblock and radiating out overnight.

 

[Piddy]

The calorifier is below the engine block. I wonder if it would help if I route the pipes downwards to stop the heat rising?
I'm wary about putting anything in the pipes that would restrict flow and put any pressure on the water pump...

 

[sarabande]

that won't work. A non return valve or even a ball valve to shut off the flow, is needed.

 

[geem]

you could fit a solenoid valve such that when you run the engine the valve is enegized to open. when you stop the engine the valve closes. This would stop the thermosyphon effect and keep the hot water in the calorifier. alternatively, just close a manual valve but you need to rememeber to open and close as you start/stop engine.

 

[theoldsalt]

Piddy,

It certainly sounds as if the calorifier is back syphoning into the engine.

Did you fit the calorifier yourself? It sounds as if the hoses are incorrectly connected to the engine. What engine do you have and where are the calorifier hoses connected to the engine cooling system?

I may not have a solution but the information may help someone more knowledgeable.

I have a calorifier fitted to my engine and lower in the boat than the engine. The engine cools down far quicker than the water in the calorifier but still doesn't back syphon, and I am not aware of a non-return valve in either hose to the engine.

 

[theoldsalt]

Piddy,

The more I think about your problem the more I am convinced it is a problem with the connections to the engine. The calorifier supply and return hoses should be connected to the engine either side of the engine thermostat so that the caloifier acts as a by-pass loop for the engine coolant pump. When the engine stops, the thermostat soon closes and with the pump stationary, water circulation can no longer take place through the calorifier.

 

[Plevier]

The calorifier supply and return hoses should be connected to the engine either side of the engine thermostat

Not always the case, e.g on my Volvo MD2020 they are both on the body of the water pump. Thermosyphoning won't happen because of the lack of a temperature gradient between them.
In fact bridging the thermostat would be bad, it would be the same as opening the thermostat early, it would let water below thermostat opening temperature through to the cooling circuit delaying engine warmup.

If you put a definite dip in the pipes between the engine and calorifier it should stop thermosyphon circulation. (You'll have to make provision for bleeding at the cal when filling.)

 

[Piddy]

Piddy,

It certainly sounds as if the calorifier is back syphoning into the engine.

Did you fit the calorifier yourself? It sounds as if the hoses are incorrectly connected to the engine. What engine do you have and where are the calorifier hoses connected to the engine cooling system?

I may not have a solution but the information may help someone more knowledgeable.

I have a calorifier fitted to my engine and lower in the boat than the engine. The engine cools down far quicker than the water in the calorifier but still doesn't back syphon, and I am not aware of a non-return valve in either hose to the engine.

The engine is a Thorneycroft T80 and the calorifier is plumbed as far as I am able to determine, in the way that Moodys intended. The pipes for the calorifier come from a part that holds the thermostat although I have never studied it in detail other than what the manual shows.... I have renewed the pipes, changed the thermostat and done normal maintenance over the last 12 years we have owned her but ostensibly all is still as original. The calorifier has never stayed warm in the time we have owned the boat suggesting nothing I have done has changed anything.
Manual:

Thanks for the comments.

 

[theoldsalt]

Hi Piddy,

We have the same engine.

This photo shows my calorifier connections on the thermostat housing.


View attachment 32013

 

[RAI]

A simple test would be to swap over the two hoses on the engine (or calorifier). See how that works.

 

[Piddy]

theoldsalt: yes, same engine but a few subtle differences - the thermostat body is rounded on yours, square on mine. yours is clean, mine isn't! I think I do see something in the pipe going away to the the calorifier - is that likely to be a non return valve?

RAI: yes, I agree. perhaps if it rains this Saturday, I'll swap them over.

Thanks again.

 

[michael_w]

Most obvious cause is there's not enough insulation on the cylinder. Buy an old fashioned hot water cylinder jacket. Made a huge difference on my boat. Also, the size of the cylinder plus how much water you've used has a considerable affect on heat retention.

 

[prv]

Most obvious cause is there's not enough insulation on the cylinder.

That was my first thought, but then he said that the engine was staying hot. So quite clearly that's where the heat is going, and insulating the cylinder won't help.

Pete

 

[theoldsalt]

theoldsalt: I think I do see something in the pipe going away to the the calorifier - is that likely to be a non return valve?


Thanks again.

Hi Piddy,

No not NRV. Each hose has a shut-off valve so that the hoses can be disconnected (if necessary) without loss of coolant. The engine manual states they must not be closed when running the engine.

 

[vyv_cox]

A dip in the hoses from the top of the calorifier down to around the lowest point then up to the engine connections will solve it. Not a problem I have had but it has come up here several times before. An alternative that will work with an indirectly cooled engine is to introduce a spring loaded non return valve. The engine pump is powerful enough to open it but convective flow will not.

 

[michael_w]

That was my first thought, but then he said that the engine was staying hot. So quite clearly that's where the heat is going, and insulating the cylinder won't help.

Pete

Cast iron engine will retain heat for ages. Occam's Razor methinks.

 

[prv]

Cast iron engine will retain heat for ages.

Not 24 hours, though.

Occam's Razor methinks.

Indeed - which is more likely?

• a calorifier which is new and therefore fairly well insulated is nevertheless inexplicably losing large amounts of heat through its walls
• the hot water is rising up the pipes, as hot water famously does, to the large engine-shaped radiator mounted above it

?

I know which seems like the simplest explanation to me.

Pete

 

[NormanS]

Mine has a non-return valve, and works.