Installing Stove with Back Boiler

[Staarek]

Hi everyone,

 

I’m looking into installing a stove with a back boiler that would serve one radiator located in the bedroom. I was thinking about Aarrow Acorn (1.2kw to water, 3.8kw to room) The Stove would be installed right at end by the stern bulkhead and the cabin is at the other end of the boat (hence the idea of additional rad as the boat is 65’ long)

 

Here’s a crude drawing:

 

 

Any other aspects I should take into account?

Will 15mm piping be sufficient or shall I run it in 22mm and then 15mm to rad’s valves? If I would want to isolate the rad can I still use the stove on its own?

 

Many thanks

[SamKingfisher]

Make sure you size the radiator so the system can't boil. With a pump 15mm pipe is fine.

put the pump on the cold side i.e. just before the boiler.

Make sure you don't build in anywhere that can be an airlock.

 

ps regarding last question - no not unless you use calorifier as heat sink and that'll only work if it's not hot.

 

good luck!

Edited April 7, 2014 by SamKingfisher

[Staarek]

Make sure you size the radiator so the system can't boil. With a pump 15mm pipe is fine.

put the pump on the cold side i.e. just before the boiler.

Make sure you don't build in anywhere that can be an airlock.

 

ps regarding last question - no not unless you use calorifier as heat sink and that'll only work if it's not hot.

 

good luck!

 

Thanks SamKingfisher. The rad is 1.2kw and I'm planning to place the header tank in the engine compartment so 1.2Kw + quite a bit of piping (around 30 m altogether) I'm hoping will be enough for the water not to boil. By saying to put the pump on the cold side, do you mean on the return?

[smileypete]

I'd go for something like this:

 

Based on adequately sized gravity rads near or next to the stove, and more distant rads on a pump.

 

That way you can choose to have all the heat going to the saloon if you wish, and are not reliant on a pump and it's 12V supply.

 

cheers, Pete.

~smpt~

[Staarek]

I'd go for something like this:

 

Based on adequately sized gravity rads near or next to the stove, and more distant rads on a pump.

 

That way you can choose to have all the heat going to the saloon if you wish, and are not reliant on a pump and it's 12V supply.

 

cheers, Pete.

~smpt~

 

Thanks Pete. Yeah, gravity option seems good as no electrical supply is needed but since I'm putting only one rad I thought that it would be easier to install circulation pump. Also I already have pipe boxing so I can hide the pipes.

[MoominPapa]

The right-hand pipe from the header tank should come from the bottom of the tank. The left-hand one should run in an inverted U, as high as possible, before descending into the top of the tank. That will give an escape path for steam, but stop the pump creating a permanent waterfall in the tank, which would aerate the water and cause corrosion. The top of the tank should not be sealed or sealable.

 

MP.

[Staarek]

The right-hand pipe from the header tank should come from the bottom of the tank. The left-hand one should run in an inverted U, as high as possible, before descending into the top of the tank. That will give an escape path for steam, but stop the pump creating a permanent waterfall in the tank, which would aerate the water and cause corrosion. The top of the tank should not be sealed or sealable.

 

MP.

Thank you MoominPapa.

 

Is this sort of thing you've got in mind:

 

[b0atman]

you need to put isolate valves near the back boiler and a drain off valve at low point between valve and back boiler for summer useage this saves draining all the system.

I think you will have problems with water boiling though.

[Staarek]

you need to put isolate valves near the back boiler and a drain off valve at low point between valve and back boiler for summer useage this saves draining all the system.

I think you will have problems with water boiling though.

 

Thanks for your reply b0atman. Will water still boil even if use 1.2kw rad (which is rated output of the boiler) and a lot of piping (30-40m) all together? Also I'm planning to put the header tank in the engine compartment which should help with cooling the water down.

[b0atman]

I have a oven thermometer on my fire top and monitor this to keep water temp under control I am feeding 3 radiators and have problems when rooms ambient temperature raises and slows heat exchange from radiator. My overflow pipe from header tank now goes into a container so if system boils and blows off then I do not lose antifreeze (using Halfords pink ready mixed).

[BEngo]

You should put the circulation pump in the lower pipe between the stove and the header tank pushing water into the stove . That way it has to deal with the cooler water and will last longer ( some are only rated to 90C and even the 100C+ rated ones are better off cooler). It will also reduce the tendency to pump water through the header tank. Fit lever stop valves either side of the pump so you can get it out without draining the whole system.

 

In theory, the 1.2 kW radiator will ensure that the system does not boil because the fire input is only 1.2 kW. That assumes that the heat can be carried away from the stove fast enough. 15mm pipe will introduce a significant flow restriction. I would use 22mm pipe and short as possible 15mm drops to the radiators. That way the system will probably thermo circulate at low power outputs, saving battery and pump life if you fit a thermostat on the pipe outlet from the stove.

 

Fill it with antifreeze and there is no need to drain down in summer.

 

N

[Staarek]

You should put the circulation pump in the lower pipe between the stove and the header tank pushing water into the stove . That way it has to deal with the cooler water and will last longer ( some are only rated to 90C and even the 100C+ rated ones are better off cooler). It will also reduce the tendency to pump water through the header tank. Fit lever stop valves either side of the pump so you can get it out without draining the whole system.

 

In theory, the 1.2 kW radiator will ensure that the system does not boil because the fire input is only 1.2 kW. That assumes that the heat can be carried away from the stove fast enough. 15mm pipe will introduce a significant flow restriction. I would use 22mm pipe and short as possible 15mm drops to the radiators. That way the system will probably thermo circulate at low power outputs, saving battery and pump life if you fit a thermostat on the pipe outlet from the stove.

 

Fill it with antifreeze and there is no need to drain down in summer.

 

N

 

Many thanks BEngo, it all start to make sense. Regarding the circulation pump, I was thinking about using webasto/eber type, would these provide enough flow?

[BEngo]

I don't really know these pumps, but as the heat output from a neverspacher etc is more than your 1.2 kW I would expect them to be OK. There is/was a suitable s/h Johnson circ pump on the Sale and Wanted pages.

 

N

[smileypete]

Do not put any valve whatsoever between backboiler top outlet and header tank vent pipe end.

 

cheers, Pete.

~smpt~

Edited April 7, 2014 by smileypete

[NorthwichTrader]

I mentioned it elsewhere, but I recently discovered to my surprise that 34ft of 15mm hep pipe held only a smidge over 1ltr of water, so between 3-4 ltr for your 30m of piping (about a kettle full), so not as much as you'd think?

Just a surprising factoid!

[Jambo]

We're looking at fitting a back boiler over the summer so I'm trying to hoover up as much info as possible on this so forgive the silly questions... but this one doesn't make sense to me:

 

Fill it with antifreeze and there is no need to drain down in summer.

 

Can someone explain why you would drain the system in summer and why antifreeze prevents this please??

[BEngo]

The antifreeze contains a corrosion inhibitor ( you could use something like Fernox or the DIY sheds' own brew instead., if the fire is going to be lit all winter) as well as glycol to keep the water liquid.. The suggestion was in response to boatman at post #8 who suggested a drain valve for summer, I assume because if all the water is drained out there won't be corrosion in the radiators and back boiler.

 

Draining down in summer (and washing the boiler fire space out with lime water) was not unusual on early solid fuelled house central heating systems IIRC.

 

N

[Jambo]

Ah ok, thank you! I was trying to work out how it might freeze over the summer....

[BEngo]

In UK?

 

N

[Staarek]

So I've got stove in its place, I run most of the pipes, I just want to double check if it's alright before I make it permanent:

 

 

The pipes are 22 mm and 15 mm to the actual rad.

 

Thanks in advance!

Edited August 21, 2014 by Staarek

[smileypete]

So I've got stove in its place, I run most of the pipes, I just want to double check if it's alright before I make it permanent:

 

 

The pipes are 22 mm and 15 mm to the actual rad.

 

Thanks in advance!

 

Errrr, not quite!

 

Move the pump and the isolation valves to the bottom left, so it pumps water from the radiator back towards the bottom inlet of the backboiler.

 

Then swap the connections to the header tank on the left, so the pipe from the top outlet of the backboiler points into the top of the header tank.

 

The top pipe on the left (vent pipe) should be 22mm, the rest can be 15mm. Could you upload a revised diagram just to be sure?

 

Would also be handy to know the output kW of the backboiler and size and type of the rad (area, double single etc), to check the rad is large enough.

 

I'm a bit puzzled as to why it's a non gravity pumped system, just to heat a single rad. Is there space near the stove for a gravity radiator, to act as a backup for the pump? If it's just to spread a bit of heat along the boat maybe try an ecofan?

 

cheers, Pete.

~smpt~

Edited August 21, 2014 by smileypete

[Staarek]

Thanks Pete. Is this sort of thing you had in mind?

 

 

The back boiler is 1.2kw and the rad is also 1.2kw (fairly big 3-column unit), there is quite a lot of piping though (around 20 m or more) so I'm hoping it's going to be enough. The single rad will be installed in the bedroom as our distribution is not great for heat distribution.

 

Forgive me stupid question, the back boiler has got 1 input & 1 output, do I connect the pipe just after the pump to the input and then it carries on from the output? Or do I have to put equal tees both on input & output ?

Edited August 21, 2014 by Staarek

[smileypete]

Ooops sorry, I actually meant move the pump and valves to the bottom RIGHT

 

If there's space near the stove at all, it could be helpful to put a gravity rad there, even if its say 700W. That way there's a choice of how much heat to keep in the saloon, and how much to heat the bedroom.

 

I expect the bedroom door could be opened to allow heat to the rest of the boat, but that may depend on layout and use. Do you know the total heat output of the stove in kW?

 

Probably best to have a large tee on the top and bottom backboiler connections to match the size of them, then go in each direction from there, reduce down if necessary with adapters. Are the backboiler connections threaded with something like 1" BSP male or female (BSP thread size not inches diameter)?

 

I'll try and do a diagram or two later myself, could help others too.

 

cheers, Pete.

~smpt~

Edited August 21, 2014 by smileypete

[b0atman]

Remember Fire keeps putting heat into the back boiler But the radiator only puts out max heat into a cold room and will put out less as room gets warmer.

[Staarek]

Ooops sorry, I actually meant move the pump and valves to the bottom RIGHT

 

If there's space near the stove at all, it could be helpful to put a gravity rad there, even if its say 700W. That way there's a choice of how much heat to keep in the saloon, and how much to heat the bedroom.

 

I expect the bedroom door could be opened to allow heat to the rest of the boat, but that may depend on layout and use. Do you know the total heat output of the stove in kW?

 

Probably best to have a large tee on the top and bottom backboiler connections to match the size of them, then go in each direction from there, reduce down if necessary with adapters. Are the backboiler connections threaded with something like 1" BSP male or female (BSP thread size not inches diameter)?

 

I'll try and do a diagram or two later myself, could help others too.

 

cheers, Pete.

~smpt~

 

Hi Pete. Thanks again. You are right, the boiler connections are 1" and I fitted 1" to 22 mm elbows. I think I'll run the pipes down and then fit 22mm tee.

Referring to the picture below I assume drawing A i correct?

 

Remember Fire keeps putting heat into the back boiler But the radiator only puts out max heat into a cold room and will put out less as room gets warmer.

 

Hmm good point... Maybe it would be a good idea to install additional rad (tower rail??) in the toilet that would be used only one the bedroom is warm enough?

Edited August 21, 2014 by Staarek