Boat Heating

[johnlowe]

I have a solid fuel stove which I would like to fit a back boiler to. I would like to plumb this into the central heating circuit which is run by a Mikuni Mx40 boiler, obviously the Mikuni will be off when the back boiler is being used, does anyone know whether this can be done, ie. will the back boiler cause any ill effects to the Mikuni with them being on the same circuit. I can't see how else I could fit a back boiler without having a second set of radiators. Thanks

[Guest]

I do know that in domestic situations a woodburning boiler is often put in series with a gas or oil boiler, but I am not familiar with your particular boiler.

[rog guiver]

Does the present installation have a seperate pump, and if so does it take its control from a thermostat?

[DaveR]

With all the problems I have had with my Mikuni I would recommend ditching it and go with the back boiler on its own. I am planning just that.

[rog guiver]

Go with DaveR's suggestion, it works for us. Two radiators pumped from the Squirrel. Very quiet Bolin pump from Kuranda is automatically switched on by pipe thermostast on output from back-boiler.

 

We have also installed a single radiator bypassing the pump that runs on convection. This allows, on returning to the marina, closing down the electrics with the fire still dying down. All remaining heat convects through the single radiator.

 

Thought of having all the boat on convection but with its length I was worried that with the water tank approaching empty/bow high I might be asking the hot water to run DOWNHILL!

Edited July 20, 2005 by rog guiver

[John Orentas]

You must be very careful about using a thermostat to control the pump in these circumstances. The energy which the water takes from the stove must go somewhere and be lost, if it is not being pumped around the radiators it will inevitably boil and blow itself out of the header tank.

[dor]

ou must be very careful about using a thermostat to control the pump in these circumstances. The energy which the water takes from the stove must go somewhere and be lost, if it is not being pumped around the radiators it will inevitably boil and blow itself out of the header tank.

 

I'm sure it's been discussed here before, but what you should do is fit a thermostat (I used a standard tank 'stat) on the output pipe close to the boiler. This is wired in parallel with the room stat, but set at about 95 deg C.

Then, if the solid fuel boiler gets near boiling, it will turn the pump on and dump heat into the radiators, even if the room 'stat thinks the room doesn't need heating.

Edited July 20, 2005 by dor

[rog guiver]

John,

 

The "normal" operation of our system is the two remote radiators are pumped with the pump being switched by the pipe stat at the output to the boiler.

 

The reason for adding an additional radiator (gravity system, bypassing the pump) is, so that if the fire is still producing heat on arrival back at the marina, we could still turn off all the electrics. Obviously I have tried it with the air inlets to the fire closed and the "gravity radiator" dissipates the heat with no problem.

 

Likewise while out and about on the boat there are times when we might visit the odd pub with the fire alight. The fire is left ticking over (with the pump armed via the stat), but should the pump fail when required to run by the stat the heat will still be dissipated through the "gravity radiator".

Edited July 21, 2005 by rog guiver

[John Orentas]

Rog.

 

I did notice that you and Dor have a mechanism that in your cases gets over the problem of using a thermostat, I was really making a general point. I am sure though it would take a while to gain sufficient confidence in the system that you could go off to the pub leaving it to do it's own thing.

[rog guiver]

John,

 

On the B777 they use "skin cooling" to cool the flight instruments cooling air just the same as the engine cooling on most narrowboats.!

 

But in the case of our heating system if it was installed on a B777 there would be three thermostats, an electric pump, an air driven pump and a hydraulic pump.

 

However I do see where you are coming from. I would like to have made the whole boat "gravity" but as I said earlier that did not seem to be an option.

[johnlowe]

Thank you all for replying to the subject, but unfortunately none of you have answered the original question, which was, can a back boiler on a solid fuel stove be plumbed into the central heating boiler system, if the answer is no then does anybody else have a back boiler and a central heating boiler, and how do they run both systems side by side, ie. do you have 2 sets of radiators. Thanks

[Paul Evans]

I'm sure this has been discussed before somewhere on the forum but I can't find the thread. As I recall the conclusion was that it is possible to connect your back boiler to the central heating system on your boat. I am no central heating engineer (Where is Big Col when you need him?) but I have put together a diagram and loaded it into the gallery HERE that I think represents the outcome of the discussion.

 

You will need shut-off valves to isolate the back boiler and/or central heating boiler - you won't be running them both at once - and non-return valves across the flow and return pipes at the "ends" of the pipe runs. You will probably need a pump for the back boiler - I'm assuming the central heating system has an integral pump - and a header tank at the highest point in the system.

 

I don't guarantee this will work - in fact I'm certain that somebody will point out the flaws in the system!

[rog guiver]

Thank you all for replying to the subject, but unfortunately none of you have answered the original question

 

John,

 

The thread drifted somewhat as you did not answer the question regarding if you present system has a seperate pump. Assuming it does then as Paul suggests two shut off valves positioned upstream of the pump, one from the output from the CH boiler and one from the output from the Back boiler would work.

 

Depending on what controls the pump there might be a change to the wiring to introduce a pipe stat on the output from the back boiler. A little more information on the present wiring would help with regard to the modifications required.

 

There should not be the need for a NRV as with the appropriate shut off valve closed then the water (via the pump) will only be able to circulate around the "active" system.

 

I would also sugest that the feed from the header tank joins the pipe work on the return from the radiators just before the pipe splits feeding the return sides of the CH boiler and Back boiler. It will then be able to feed whichever system is active.

Edited July 23, 2005 by rog guiver

[johnlowe]

Rog

 

The only pump I have on the system is the integral one fitted to the Mikuni boiler, which in turn is directly wired to the dc distribution board. Thanks John

[rog guiver]

John,

 

In that case the new pump could be placed in the output from the squirrel prior to it merging with the output from the Mikuni (on its way to the radiators).

 

There would have to be the facility to turn off the power supply to the Mikuni (as well as closing the associated shutoff valve) when the squirrel is lit (its shutoff open). The control of the pump, yet again with a switch, could simply (as described earlier) be switched by a pipe stat.

 

On the occasion when the squirrel is not lit CH would be available as at present from the Mikuni. (Mikuni switch on, shutoff open, Squirrel switch off and shutoff closed). The two switches could be combined into one "two way" switch.

Edited July 24, 2005 by rog guiver

[DaveR]

Shouldn't the pump to be on the inlet side?

 

I was always told the pump should shift the water at its coolest point.

[dor]

To answer your original question (more or less) - whilst I haven't done it on a boat, I have done it on a domestic system - i.e. plumbed a solid fuel stove in parallel with an oil boiler. Used a thermostat on the back of stove to turn pump on if it was getting too hot. Worked no problem and I see no reason why a similar setup shouldn't work on a boat. The stove acts as a pre-heater to the boiler.

[stuart]

Quick question about thermostats... How are you attaching them to the boiler/pipe work?

 

The back of my stove is too hot for the thermostat - I'm worried that the plastic casing will melt- it gets VERY hot (too hot to touch)

[dor]

The thermostat goes on the water pipe outlet from the back boiler, not on the stove itself. A standard tank stat does hte job, wired up in parallel to anything else so it effectively overrides any controls and turns the pump on. I had mine set to 95C, the idea being that it would turn the pump on and dump heat before the water in the back boiler boiled.

 

You need to be careful if you have TRVs - as with any system using a solid fuel stove with back boiler you should have at least one rad without a TRV, and preferably able to themo-syphon.

[rog guiver]

Tank stats are designed to fit around a tank (with the long strap)

 

Pipe stats are designed to fit around any pipe (15mm to 28mm).

 

As the pipe stat "sensing surface" is designed around a diameter of 15mm to 28mm, rather than the tank stat around a diameter of approx 450mm, it is more accurate. Also it comes with two springs coils to fix it to the pipe.

 

With regard to the heat they are all designed to work in a very hot location but it is worthwhile using the correct heat resistant cable at least for the first 500mm from the stat.

Edited July 25, 2005 by rog guiver

[johnlowe]

Ok, these answers are really helpful, but just one last question. What size pipe should be used for the back boiler. The Mikuni runs into 15mm pipe, can this be used or does a back boiler use a different size. Thanks John

[dor]

Pipe stats are designed to fit around any pipe (15mm to 28mm).

 

As the pipe stat "sensing surface" is designed around a diameter of 15mm to 28mm, rather than the tank stat around a diameter of approx 450mm, it is more accurate. Also it comes with two springs coils to fix it to the pipe.

 

Fair comment Rog - when I first did it, I don't think pipe stats were around!

[rog guiver]

The output in our system from the squirrel is in 28mm but that is routed to the one "by gravity" radiator. The rest of the system is in 15mm.

 

In your case I think it would be worthwhile having a short length of 28mm then reduce it down to 15mm(I seem to remember the outputs are 1 inch BSP). This would allow the water to move within the pipe as it heats up prior to the stat starting the pump.

 

One last comment, the squirrel ash removal system is not that good with buildups around the round grate. They do two inserts (as optional extras) that fit each side of the grate and direct the ash towards the middle. They have worked well but did need a little attention (with the grinder) prior to fitting as they fouled the back boiler.

Edited July 25, 2005 by rog guiver