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Backboiler question


Jenwil

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11 hours ago, Tom Richmond said:

Having just installed a pumped radiator system in my boat, I can confirm that rads come with 1/2 bsp female threaded inlets and outlets, and therefore can easily be connected to without proprietary valves. Any 1/2bsp threaded fitting will work (nb: 15mm compression uses 1/2bsp thread so you could use a normal 15mm fitting without the olive and collar.

Reason for smaller pipe in the diagram is mostly dictated by the inlet size on the rads (as indicated above, 15mm is ideal) but also, even if total flow from backboiler is through 28mm pipe, each rad only uses a portion of that flow, so 15mm should be adequate. Lastly, 15mm much easier to make fiddly connections to rads, and can be made to look much nicer.

Can I ask what circulation pump you are using, and what it needs to run please, I may consider this as an option too.

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7 minutes ago, Jenwil said:

Can I ask what circulation pump you are using, and what it needs to run please, I may consider this as an option too.

 

If you're fitting a circulation pump then the whole system design can change, and a whlo load of different problems present themselves.

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10 minutes ago, Jenwil said:

Can I ask what circulation pump you are using, and what it needs to run please, I may consider this as an option too.

I am using a jabsco ecocirc. Not cheap, but widely agreed to be very efficient. I got mine from Mack Engineering, cheapest place I have found for pumps...

It is rated to draw 1.7a, but has a variable speed setting. I run mine on about 2 (out of 5) and it draws less than half an amp. My inverter standby load is more than the pump... Obviously pump also does not run all the time... I could run in on the lowest speed as it still shifts the coolant, but it is so quiet that I can't hear it, and i like to hear it coming on to know everything is working right.

I went for a pumped system because I do not have a straight run between all my rads (mostly I have a doorway in the side of the boat which pipework needs to pass beneath). It was relatively cheap and easy to run plastic push fit plumbing to all rads, so you can offset the saving in thick copper against significant cost of the pump.

Disadvantage is that if the pump fails you have no way of moving the coolant and it will boil. Need to ensure you have a feed and expansion tank close to stove so that this can happen relatively safely. I am lucky that my stove is a rayburn in the kitchen and my feed and expansion tank sits over the sink (and yes, it has boiled a few times as I have been working the system out...)

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1 hour ago, Mike the Boilerman said:

 

Having cupboards where the pipes need to go seems a bit strange too! ;)

The cupboards were there first:)

1 hour ago, rusty69 said:

28mm and 15mm (to rads). Normal rad valves fitted.

Can you draw a pic of your setup please?

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18 minutes ago, Jenwil said:

The cupboards were there first:)

Can you draw a pic of your setup please?

Our setup is very similar to the pic you already posted,but with three rads,and the drain point near the lowest point in the system. If doing it again, I wouldn't bother with the valves (have been meaning to take them out). The pipework has a gentle incline to the last rad. The stove is near the front of the boat,and the last rad in bedroom of a 70ft boat.

13 minutes ago, Jenwil said:

So if the pipes go through the cupboards how do I get the rise to go up (behave rusty)

I said nothing:)

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I did a sample layout diagram a while back which may help:

gallery_2174_346_1611.png

Some things worth mentioning are

- There must be NO valve between backboiler top outlet and header tank vent pipe (v. important!!!).

- The top of the gravity fed radiators should be as high as poss compared to the backboiler top outlet.

- The heat output of the gravity fed rads should largely match the heat output of the backboiler, say at least 70% to 80%

- If a pump is needed the cheap 100°C rated 'solarproject' type pumps are reported to work well.

- The gravity fed rads can be near or next to the stove which allows more choice over where the heat is output to.

- The incline on the pipes to the gravity fed rads is more about making that part of the system 'self bleeding' of trapped air.

All that said backboilers are more worthwhile for off grids boats largely occupied 24/7 in winter, for partly occupied boats that some quick heat at the other end once or twice a day, there's also blown air diesel and propane heaters like Eberspacher and Propex.

Edited by smileypete
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On 04/12/2017 at 23:08, Jenwil said:

So the pipe goes in at the top right, out the top left in a kind of circle then back in at the bottom left and out the bottom right and so on if not using valves?

thanks guys.

??

The flow comes out of the top of the boiler, into one or both connections at the top of each radiator, out of the bottom connection(s) of each radiator and back to the bottom of the boiler. With or without valves.

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18 hours ago, smileypete said:

I did a sample layout diagram a while back which may help:

gallery_2174_346_1611.png

Some things worth mentioning are

- There must be NO valve between backboiler top outlet and header tank vent pipe (v. important!!!).

- The top of the gravity fed radiators should be as high as poss compared to the backboiler top outlet.

- The heat output of the gravity fed rads should largely match the heat output of the backboiler, say at least 70% to 80%

- If a pump is needed the cheap 100°C rated 'solarproject' type pumps are reported to work well.

- The gravity fed rads can be near or next to the stove which allows more choice over where the heat is output to.

- The incline on the pipes to the gravity fed rads is more about making that part of the system 'self bleeding' of trapped air.

All that said backboilers are more worthwhile for off grids boats largely occupied 24/7 in winter, for partly occupied boats that some quick heat at the other end once or twice a day, there's also blown air diesel and propane heaters like Eberspacher and Propex.

So you have used 28mm t's not 28mm to 15mm ?

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On 12/6/2017 at 12:15, Jenwil said:

So you have used 28mm t's not 28mm to 15mm ?

Sorry for the late reply...

I s'pose 15mm should work OK for the 'tails' off the main run if we're talking about several small rads running off a smallish back boiler.

Some people put the flow and return at diagonal corners for the gravity rads but I doubt this makes much difference, and might make it trickier to change the radiator later on for a bigger/smaller one if need be.

Edited by smileypete
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2 minutes ago, smileypete said:

Sorry for the late reply...

I s'pose 15mm should work OK for the 'tails' off the main run if we're talking about several small rads running off a smallish back boiler.

Some people put the flow and return at diagonal corners for the gravity rads but I doubt this makes much difference, and might make it trickier to change the radiator later on for a bigger/smaller one if needed.

Thats how ours is wired.

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Just now, rusty69 said:

Thats how ours is wired.

Yeah I'm just thinking that if there's some space to one side of the gravity rads then they can be swapped round to change the heat output in different locations, in case the more distant ones aren't giving out enough heat.

With a diagonal connection it might be more tricky if all soldered in, with connections one one side it might just mean undoing the compression to 1/2 BSP that connects into the rads.

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3 minutes ago, smileypete said:

Yeah I'm just thinking that if there's some space to one side of the gravity rads then they can be swapped round to change the heat output in different locations, in case the more distant ones aren't giving out enough heat.

With a diagonal connection it might be more tricky if all soldered in, with connections one one side it might just mean undoing the compression to 1/2 BSP that connects into the rads.

Ours are diagonal. But, I see what you mean about connecting them on one side,but may be detrimental to the flow through rad and hence heat?

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