Hydronic type water heating basics

[jmnapier]

Morning All
I currently have a 30 litre calorifier with a 1250W immersion coil plus a circuit from the left engine. Having just spent a week in the Scillies hot water has been a problem.
How does the Hydronic system work? Does it supply a second hot water circuit that heats the calorifier in the same way as an engine coolant circuit? Or does it heat water as you use it like a Vaillant domestic boiler? (I already have an Eberspacher air heater so am not interested in the central heating options of the hydronic, or the engine pre-heating options).
Many thanks Jonathan

 

[geem]

Morning All
I currently have a 30 litre calorifier with a 1250W immersion coil plus a circuit from the left engine. Having just spent a week in the Scillies hot water has been a problem.
How does the Hydronic system work? Does it supply a second hot water circuit that heats the calorifier in the same way as an engine coolant circuit? Or does it heat water as you use it like a Vaillant domestic boiler? (I already have an Eberspacher air heater so am not interested in the central heating options of the hydronic, or the engine pre-heating options).
Many thanks Jonathan

The best way is to have a second coil in the calorifier. The hydronic heater will then heat up the water in the calorifier via a closed loop, separate from the engine cooling circuit. It's just a diesel heater that heats water instead of air. You need an expansion/filler tank but that is all easy to see if you down load the webasto hydronic heater manual.
We recently replaced our aged calorifier with a two coil 30L unit and installed the webasto hydronic. Hot water at the push of a button and a 15min wait.
I believe some of the cheapo Chinese hydronic heaters are pretty good. Might be worth a look

 

[Ian_Edwards]

Hydronic system heat the domestic hot water in the calorifier via a coil in exactly as the engine.
My Hydronic 10 systems has 2 coils in the calorifier, one for the engine, one for the Hydronic 10.
If you look in the vast array information online, you'll find that it is possible for the engine and the Hydronic to share the same coil. That isn't common practice on boats. I guess because it could compromise the engine cooling system.

 

[vyv_cox]

It is quite easy to form an airlock in calorifier pipework. I find the best way to check is to remove a hose at the highest point and run lots of water/coolant through, catching the overflow in a suitable vessel.

 

[geem]

It is quite easy to form an airlock in calorifier pipework. I find the best way to check is to remove a hose at the highest point and run lots of water/coolant through, catching the overflow in a suitable vessel.

Airlocks aren't normally a major problem if you have the expansion vessel connection immediately before the pump. If the pump has a good water flow then they will often push the air back around to the expansion tank. It normally helps to leave the expansion tank lid off whilst you blead the system.
Also creating a bit of head to the expansion vessel helps.

 

[jmnapier]

Thank you all for the replies. That seems simple enough. There is a place to fit the hydronic unit nearby the calorifier.
However…. It is a single coil/circuit calorifier. I guess for this to work I’d have to T the unit ‘in parallel’ across the two engine supply/feed pipes to allow circulation? Is it ok to run with engine coolant as the heated medium? Again, thanks for these basic lessons in system design. It is literally this simple a system I seek.
Cheers Jonathan

 

[geem]

Thank you all for the replies. That seems simple enough. There is a place to fit the hydronic unit nearby the calorifier.
However…. It is a single coil/circuit calorifier. I guess for this to work I’d have to T the unit ‘in parallel’ across the two engine supply/feed pipes to allow circulation? Is it ok to run with engine coolant as the heated medium? Again, thanks for these basic lessons in system design. It is literally this simple a system I seek.
Cheers Jonathan

You can run it into the engine cooling circuit but you may need to isolate the circuit from the engine everytime you use the hydronic heating system other wise you may just circulate around the engine and waste some of your heat. I didn't go that route as I didn't want to complicate the engine cooling circuit. I just changed to a twin circuit calorifier as mine needed replacement anyway

 

[jmnapier]

You can run it into the engine cooling circuit but you may need to isolate the circuit from the engine everytime you use the hydronic heating system other wise you may just circulate around the engine and waste some of your heat. I didn't go that route as I didn't want to complicate the engine cooling circuit. I just changed to a twin circuit calorifier as mine needed replacement anyway

Thanks geem. My calorifier is only 4 years old and a twin coil replacement the same is about £700 so I may just accept the compromise. Does the engine driven coolant pump not prevent flow around the engine when the engine isn’t running? I think maybe that’s wrong otherwise the hydronic unit wouldn’t be offered as an engine preheat system.

 

[geem]

Thanks geem. My calorifier is only 4 years old and a twin coil replacement the same is about £700 so I may just accept the compromise. Does the engine driven coolant pump not prevent flow around the engine when the engine isn’t running? I think maybe that’s wrong otherwise the hydronic unit wouldn’t be offered as an engine preheat system.

They are offered as engine preheat systems. Hopefully somebody who has plumbed theirs into the cooling system can advice

 

[Steve_N]

I added a Hydronic heater to an existing single-coil calorifier using a pair of T valves which would either isolate the engine circuit or the Hydronic circuit. It's a good few years ago now and I'm struggling to recall the precise details but I know that a) it did work fine and b) it was a pain in the ar$e as it required 2 header tanks, one for whichever circuit was active. Not for the faint-hearted.
If I was doing the same again, i.e. wanting to retain a single-coil calorifier but add a Hydronic, I would just plumb the Hydronic alone to the calorifier and forget the 'free' heat from the engine; the Hydronic was very efficient plus I enjoyed using it (small boy at heart..).

 

[geem]

I added a Hydronic heater to an existing single-coil calorifier using a pair of T valves which would either isolate the engine circuit or the Hydronic circuit. It's a good few years ago now and I'm struggling to recall the precise details but I know that a) it did work fine and b) it was a pain in the ar$e as it required 2 header tanks, one for whichever circuit was active. Not for the faint-hearted.
If I was doing the same again, i.e. wanting to retain a single-coil calorifier but add a Hydronic, I would just plumb the Hydronic alone to the calorifier and forget the 'free' heat from the engine; the Hydronic was very efficient plus I enjoyed using it (small boy at heart..).

I would concur. Being a 5kw heater, on a 30L calorifier, you get a full tank of hot water very quickly. If you spend a lot of time at anchor, it would make a lot of sense

 

[jmnapier]

I added a Hydronic heater to an existing single-coil calorifier using a pair of T valves which would either isolate the engine circuit or the Hydronic circuit. It's a good few years ago now and I'm struggling to recall the precise details but I know that a) it did work fine and b) it was a pain in the ar$e as it required 2 header tanks, one for whichever circuit was active. Not for the faint-hearted.
If I was doing the same again, i.e. wanting to retain a single-coil calorifier but add a Hydronic, I would just plumb the Hydronic alone to the calorifier and forget the 'free' heat from the engine; the Hydronic was very efficient plus I enjoyed using it (small boy at heart..).

That is a bloody good idea… lateral thinking, works every time!
Thanks again everyone