A few back boiler questions...

[sociable_hermit]

Fairy Nuff. A header from the top of the radiator will still end up collecting air from the system - if it can find its way to the top of the rad, it'll find its way to the top of the header tank eventually. But yeah I see what you mean about the header heating up too much. I think I've been lucky as my header tank is in the engine room about 6' from the one and only radiator, and at least 6" higher up, with quite a slim pipe. So it gets warm and keeps the frost away, but that's all.

[Canal Shop Man]

Just to confuse you all, I have a pressurised system!

 

It is tee-ed off the fresh water supply after the pump, has an accumulator tank and pressure relief valve and then goes into the circuit (which in my case goes to the calorifier). It works very well. The benefit is that, with a 40psi water pump, the water can get up to 131 degrees without boiling, so you can get a lot of heat out of it. It also doesn't need a header tank as the accumulator tank allows for expansion and contraction, whilst the water pump replaces any losses. It uses a gravity feed system in 22mm pipe.

[blackrose]

Hi,

 

I tend to agree with the comments about not fitting pressurised hot water systems. I suggested connecting the expansion tank to the lower pipe as I have found that connecting said tank to the highest point leads to one having an expansion tankful of hot water - a steaming extravagance.

 

Once the air has been drained out of the radiator no further bleeding should be needed and hopefully water in the expansion tank will remain cool.

 

I did try having the header tank coming off the bottom run (but higher than the rest of the system) when I first installed my stove, but it made a lot of noise and needed constant bleeding. I couldn't work out where all the air was coming from - but it kept coming for months! Eventually I changed the position of the header tank and Td it off the top run. It ran like a dream - no noise and no more air to bleed. Yes, the water in my header tank gets warm but it's only a little bit of water (half full at maximum expansion), so it's not really wasting any energy and the rads still get just as hot as before.

[Smelly]

I did try having the header tank coming off the bottom run (but higher than the rest of the system) when I first installed my stove, but it made a lot of noise and needed constant bleeding. I couldn't work out where all the air was coming from - but it kept coming for months! Eventually I changed the position of the header tank and Td it off the top run. It ran like a dream - no noise and no more air to bleed. Yes, the water in my header tank gets warm but it's only a little bit of water (half full at maximum expansion), so it's not really wasting any energy and the rads still get just as hot as before.

 

I had exactly the opposite experience... wierd. I don't understand how you'd get more air in if it's into the bottom of the run.

 

My header's teed off both with a valve on the top run, that way I can fill to the bottom of the run and it doesn't need much bleeding. You can "tune" the valve on the top, basically turn it right down so it's barely open and it creates a self bleeding system. I've never needed to bleed my system once it's full and it gets good and hot. A problem with the top run is that if your coolant runs down it sucks air in and you struggle to get it out again.

 

Anyways Kay, one thing to note is that water cools, gets denser and sinks to the bottom of the radiator, it's partly this pressure gradient that pushes the water round the system, it's best to have the water flowing diagonally across the radiator or it'll possibly just run down the piped end of the panel.

 

Having your header as far away from the boiler is a good idea as it'll prevent any boiling water, the pressure of which is helping with the whole pushing thing, from venting before it's pushed as much as it can. It minimises the need for pressurising the system.

 

I wouldn't play with a pressurised system as I don't trust my plumbing enough. It's all well and good knowing how to fasten two pipes together but a dodgy joint you could end up spraying boiling water everywhere. Even with a domestic 3 bar PRV it goe's a fair way through a small hole.

 

One system I'll play with in time is part gravity part pumped. That way it'll spread better but I don't need a pump running my batteries down whenever the fire's lit (24/7 in the winter).

 

If you use a big enough header; ours is a gallon, then you're not worried about it boiling over.

 

Chris (Pink) where did you get your header from? I searched everywhere anyone suggested, including google, and couldn't find one big enough.

[sociable_hermit]

it's best to have the water flowing diagonally across the radiator or it'll possibly just run down the piped end of the panel.

 

I agree with you wholeheartedly on the theory, but in practice I have both pipes in one end of the rad and it all still gets nice and hot.

[kayDee]

I'm a bit unsure about the gravity system now due to getting the pipe run right and the cost of the larger copper pipe stuff. The run goes through kitchen cupboards, behind the fridge, through three door frames and trying to get an accurate incline on pipes like that is going to be very hard for us amateurs! I think it might be easier to run two 15mm pipes nice and straight and then put a pump in the kitchen cupboard on the return run. This way, we could add another radiator a bit further down the run if we needed it. We'll have to just cope with the pump noise (perhaps try and muffle it somehow). I realise that the pump will need to be on whenever the fire is on. What will happen if we forget to put the pump on and there is static water in the back boiler? Will it blow up?

Kay

x

[wonderdust]

Add a pipe thermostat to the pump like This

[kayDee]

Add a pipe thermostat to the pump like This

 

I like that idea! Pipey gets hot - pumpy switches on! So simple when you know what you're doing!

Thank you for that, that's perfect!

Kay

x

[turnbuttonboy]

I mentioned it on another posting a couple of weeks ago but it might be worth mentioning again - the simplest way to avoid both a gravity system and a continuously running pump, is to use a pipe thermostat on the hot out pipe from the boiler connected to a relay that kicks the pump in as the thermostat closes. It worked a treat on our narrowboat for years (it was a tug style so we lacked the height for a gravity system) and it means that the pump only runs intermittently, and then only when the water is hot. Total cost was about £20. Having said all that I still think that a gravity system is the way to go if possible and have set the new boat's heating up this way. You don't say what stove you are using but it is worth checking that one radiator is going to be big enough to lose the full output of the back boiler.

 

Having posted this I now see that Wonderdust has made the same suggestion!!!

 

Giles

Edited October 22, 2008 by turnbuttonboy

[wonderdust]

Can i ask why you have the relay as our system does not?

 

I mentioned it on another posting a couple of weeks ago but it might be worth mentioning again - the simplest way to avoid both a gravity system and a continuously running pump, is to use a pipe thermostat on the hot out pipe from the boiler connected to a relay that kicks the pump in as the thermostat closes. It worked a treat on our narrowboat for years (it was a tug style so we lacked the height for a gravity system) and it means that the pump only runs intermittently, and then only when the water is hot. Total cost was about £20. Having said all that I still think that a gravity system is the way to go if possible and have set the new boat's heating up this way. You don't say what stove you are using but it is worth checking that one radiator is going to be big enough to lose the full output of the back boiler.

 

Having posted this I now see that Wonderdust has made the same suggestion!!!

 

Giles

[kayDee]

I mentioned it on another posting a couple of weeks ago but it might be worth mentioning again - the simplest way to avoid both a gravity system and a continuously running pump, is to use a pipe thermostat on the hot out pipe from the boiler connected to a relay that kicks the pump in as the thermostat closes. It worked a treat on our narrowboat for years (it was a tug style so we lacked the height for a gravity system) and it means that the pump only runs intermittently, and then only when the water is hot. Total cost was about £20. Having said all that I still think that a gravity system is the way to go if possible and have set the new boat's heating up this way. You don't say what stove you are using but it is worth checking that one radiator is going to be big enough to lose the full output of the back boiler.

 

Having posted this I now see that Wonderdust has made the same suggestion!!!

 

Giles

 

Thanks Giles, I still appreciate the reply!

Kay

x

 

 

Thanks Giles, I still appreciate the reply!

Kay

x

 

Oh, do these things need power or are they just a bi-thermal strip and a switch?

[wonderdust]

Yes they are conected via 12v to the pump.

[kayDee]

Yes they are conected via 12v to the pump.

 

Thanks for that! The electrics is the simple bit - its just the pipework that will be a nightmare! Haha!

Kay

x

[Smelly]

If you're going 'lectric can I suggest a small solar panel to cushion the impact on your batteries.

 

I knew a chappie, he had a big wind gennie admittedly but never ran his engine. When his batteries died he couldn't light his stove, a panel might have helped.

[wonderdust]

These are not bad for power consumption fairly quite as well click there are others available im sure others will give you ideas.

[turnbuttonboy]

Wonderdust - We put our pump in the engine bay next to the batteries and it seemed easier to run light cables through to the thermostat and return to the relay which meant that we only had a couple of feet of power cable to supply the pump. It was probably overkill but never let us down.

 

Giles.

[kayak]

If you were just using a pump and not relying on gravity can you connect both the inlet and outlet pipe to the radiators at opposite sides at the bottom like on a domestic set up?

 

Kayak.

[wonderdust]

Yes

 

 

If you were just using a pump and not relying on gravity can you connect both the inlet and outlet pipe to the radiators at opposite sides at the bottom like on a domestic set up?

 

Kayak.

[NBMike]

If you were just using a pump and not relying on gravity can you connect both the inlet and outlet pipe to the radiators at opposite sides at the bottom like on a domestic set up?

 

Kayak.

 

Radiators will always have a better output if connected Top In - Bottom Out.

[FadeToScarlet]

Before you take this advice you should seek the advice of a professional. My understanding is that you should never run a solid fuel boiler with a pressurerised system as the heat source is uncontrolable (IE you cant turn it off instantly like you can with gas & oil) so you could be creating a large pressure bomb.

 

 

 

Justme

 

My back boiler was pressure tested to 1000 PSI...

 

It's 15mm steel plate, welded internally and externally, by a friend of the previous owner who was more used to making things to withstand industrial pressures....

 

However, the pipes and rad aren't,of course.

[smileypete]

I'm a bit unsure about the gravity system now due to getting the pipe run right and the cost of the larger copper pipe stuff. The run goes through kitchen cupboards, behind the fridge, through three door frames and trying to get an accurate incline on pipes like that is going to be very hard for us amateurs! I think it might be easier to run two 15mm pipes nice and straight and then put a pump in the kitchen cupboard on the return run. This way, we could add another radiator a bit further down the run if we needed it. We'll have to just cope with the pump noise (perhaps try and muffle it somehow). I realise that the pump will need to be on whenever the fire is on. What will happen if we forget to put the pump on and there is static water in the back boiler? Will it blow up?

 

If the pipe run to the back of the boat is toooo far and complicated to be gravity fed, I would...

 

Have a gravity fed rad in the saloon fed from 28mm and a pumped rad in the bedroom fed from 15mm.

 

Then you can have all the heat in the saloon if you like, and switch the pump on to heat the bedroom before bed-i-bies.

 

This would also allow a rad thermostat to be fitted to the bedroom rad to stop the bedroom getting too hot.

 

Also if the pump stops working you're not stuck without being able to use the stove.

 

cheers,

Pete.

[kayDee]

If the pipe run to the back of the boat is toooo far and complicated to be gravity fed, I would...

 

Have a gravity fed rad in the saloon fed from 28mm and a pumped rad in the bedroom fed from 15mm.

 

Then you can have all the heat in the saloon if you like, and switch the pump on to heat the bedroom before bed-i-bies.

 

This would also allow a rad thermostat to be fitted to the bedroom rad to stop the bedroom getting too hot.

 

Also if the pump stops working you're not stuck without being able to use the stove.

 

cheers,

Pete.

 

Mmmm, will have to have a think about that one. How would both rads be piped into the back boiler? I think it only has two holes in it...

Good idea though, I was worried about the pump stopping and what might happen to the water in the boiler...

Kay

x

[NB Esk]

My back boiler was pressure tested to 1000 PSI...

 

It's 15mm steel plate, welded internally and externally, by a friend of the previous owner who was more used to making things to withstand industrial pressures....

 

However, the pipes and rad aren't,of course.

 

Might not be *fully* welded internally........

[FadeToScarlet]

Might not be *fully* welded internally........

 

It's a good point- I was wondering how he managed that!

[Guest TerryL]

Before you take this advice you should seek the advice of a professional. My understanding is that you should never run a solid fuel boiler with a pressurerised system as the heat source is uncontrolable (IE you cant turn it off instantly like you can with gas & oil) so you could be creating a large pressure bomb.

Justme

Right, I've read all the posts and seen the pictures and as a practicing heating engineer amongst other things I'm more than a bit concerned, so can I give a bit of safety advice here from knowledge and experience? In domestic properties the installation of heating equipment is controlled by building regulations which have become much more stringent in recent years. The safety issues have evolved over many years from experience with associated disasters both in domestic and commercial situations.

 

The problem with solid fuel and certain other boilers is that they cannot be stopped easily so the installation needs to be arranged so that the heat still being produced is safely controlled should something go wrong such as a pump or circulation failure or running out of water. If it is not controlled then steam will be produced which at 100oC expands 1600 times the original water volume. The resulting rapid expansion and increase in pressure will soon find any weak spot in a heating installation and invariably cause a steam explosion which is made even worse by the sudden pressure reduction and the resulting lower boiling point. I do not recommend death by scalding steam which will fill your whole boat!

 

Pressurised or sealed systems are not permitted in solid fuel systems in the UK. In some countries they are allowed with a mains water fed heat dump system but failure of this system has caused deaths and injury. A fully vented system is the safest with at least part of the installation being capable of gravity circulation, usually the open vented hot water tank and/or a radiator. This should have a heat resistant open expansion tank situated above the highest point of the system with a cold fill pipe to the bottom of the boiler and a vent/steam pipe from the top of the boiler back over the expansion tank with an air break. The tank will also need a ball valve for automatic top up for evaporation and to replace water lost by steam.

 

If the system cannot use the heat being produced then it will increase in temperature. The water in the gravity circuit will then transfer more heat to the hot water cylinder and/or heatleak radiator, the hotter they are the more heat is released. Usually this is sufficient to prevent the water boiling but if not then the steam and water can escape over the expansion tank. As the steam is released it takes with it quite a lot of the excess heat and as the water level falls it is replenished with the cold supply which then goes down to the boiler to help cool it. The open vented hot water tank is also arranged to vent steam into the domestic cold fill tank as the hot tank water overheats, releasing more heat the same way.

 

Unvented hot water tanks as your calorifier will be are not permitted in domestic properties with uncontrolled boilers. Rubber hoses secured with jubilee clips and plastic containers etc. are also a definite no no anywhere. All copper pipe in the right sizes for the gravity systems and plastic for the remaining pumped system is the minimum requirement that I would suggest. A poor and unsafe system could affect any insurance claims!

 

As you can see there could be considerable, if not insumountable problems involved or maybe just clever thinking needed in order to install a really safe solid fuel boiler system in a boat. I'm going to take a break now to let you think about it and wait for the usual replies claiming I'm scaremongering, it's your life!