pump on solid fuel to overcome pipe drop

[john5711]

Hi
Looking at some time connecting my solid fuel boiler up to HW cylinder, problem i have is where cylinder is the first floor drops by about 350mm
so can not get a continues rise in pipe work, attached should be a diagram i think would overcome this issue, can you see any issues with what i have drawn? if the pump was to fail it is on the return side so if water in boiler got too hot the is no restriction to the vent pipe, also the is the heat sink rad, but not sure if the pump been in that position if it failed would restrict the return to much from the heat sink rad, if i put the pump before the return do you think the pump would interfere with the return as it would be positive pressure,
Thanks
John

 

[SimonG]

What part of the country you in? Just want to make sure nowhere near me.

This is not a DIY job, it needs a competent, experienced individual to sort it.

 

[john5711]

What part of the country you in? Just want to make sure nowhere near me.

This is not a DIY job, it needs a competent, experienced individual to sort it.

I know its not a DIY job just asking a second opinion if that's the best way to overcome a drop of 350mm,

 

[SimonG]

I know its not a DIY job just asking a second opinion if that's the best way to overcome a drop of 350mm,

NO.

 

[ShaunCorbs]

Can’t have a drop or trap

 

[john5711]

so what your saying is basically the solid fuel boiler can not be connected to the cylinder because of a 350mm drop and a circulation pump wouldn't over come the problem, and the is no other way round it?

 

[SimonG]

so what your saying is basically the solid fuel boiler can not be connected to the cylinder because of a 350mm drop and a circulation pump wouldn't over come the problem, and the is no other way round it?

Not saying there isnt a way round it, just that your way isnt it.

 

[Ric2013]

Not a 'competent person', but have seen a few woodburner systems. I'm not commenting on your specific house, so take these as general comments.

I wouldn't rely on a cylinder to be the primary circulation as once the cylinder is hot, convection goes down to near zero anyway. You need 2 things: constant circulation (by gravity) AND a vent. You are correct to say the pump must not be on the heat-leak circuit. You can use separate tappings for gravity and pumped circulation at the boiler, or go down the injector tee path which would ensure you don't have the risk of the pump fighting the convection in the gravity part of the circuit.

Who's to say the cylinder will be the the main place the heat goes anyway? You could have a gravity-fed radiator which, if large enough, could be your primary circulation [edit: need to make sure this CANNOT airlock] and then you will pump everything else. If your system is designed such that the cylinder is no longer integral to the safety of the system, then there's no real reason not to have the cylinder pumped on drops.

22mm is almost certainly too small for the vent. Imagine the water in the boiler expanding to 1600x its volume and you'll understand why we like to overengineer for the worst thing that might happen. The risk with this kind of system is that gravity systems have become a niche product, and not everyone understands them now, so sometimes normal practice will not be safe.

 

[ShaunCorbs]

so what your saying is basically the solid fuel boiler can not be connected to the cylinder because of a 350mm drop and a circulation pump wouldn't over come the problem, and the is no other way round it?

Correct the flow always has to rise and return has to drop / fall back to burner can’t have a pump on it to push / get over a drop / trap as you always need flow else it’s a bomb

Other than boxing in so that the flow always rises and return drops etc no

Or move the cylinder/ thermal store

 

[john5711]

Correct the flow always has to rise and return has to drop / fall back to burner can’t have a pump on it to push / get over a drop / trap as you always need flow else it’s a bomb

Other than boxing in so that the flow always rises and return drops etc no

Or move the cylinder/ thermal store

Forgetting the pump, what would be the difference from my 350mm drop, and solid fuel boiler on ground floor with flow and return rising up to the attic running across the attic then down to a cylinder on the first floor?

 

[ShaunCorbs]

Forgetting the pump, what would be the difference from my 350mm drop, and solid fuel boiler on ground floor with flow and return rising up to the attic running across the attic then down to a cylinder on the first floor?

You can’t run it up and back down as gravity doesn’t work like that

 

[Ric2013]

What sort of boiler are we talking about? Because we're all assuming it's an uncontrolled heat source that relies on gravity for safety... but it may not necessarily be so!

 

[john5711]

You can’t run it up and back down as gravity doesn’t work like that

View attachment 78856

You can’t run it up and back down as gravity doesn’t work like that

View attachment 78856

See attached picture, it shows solid fuel boiler on ground floor, gravity flow and return pipe going up to the attic, across the attic down to the cylinder on the first floor, this still works at the cylinder is higher than the boiler, plus how could it possibly be a bomb as you have a vent pipe on the heights point of the flow pipe, or do you think the Heating and Plumbing association of Ireland have got it wrong?

 

[ShaunCorbs]

That’s way different that having a drop and rise / trap before the header thank hence if it boils will have no where to go hence bomb as the drop / rise won’t flow so acts like a trap, trapping the water

If you look on the flow there’s a safety discharge/ valve and the feed teed into the return at boiler so if does boil the tank will refill with cold and safety will blow the boiling water out

It’s not the best design but will work but normally find it’s noisier as the flow has to cool a bit for it to drop and start the circulation on start up

Also we’re not in Ireland hetas is our solid fuel body

 

[john5711]

That’s way different that having a drop and rise / trap before the header thank hence if it boils will have no where to go hence bomb as the drop / rise won’t flow so acts like a trap, trapping the water

If you look on the flow there’s a safety discharge/ valve and the feed teed into the return at boiler so if does boil the tank will refill with cold and safety will blow the boiling water out

It’s not the best design but will work but normally find it’s noisier as the flow has to cool a bit for it to drop and start the circulation on start up

Also we’re not in Ireland hetas is our solid fuel body

Yes i see what you mean about the rise back up to the cylinder, if in the rise to the cylinder instead of a elbow in to the cylinder you put a tee on then had a second vent pipe going up that would solve the problem of trap for the hot water would it not? so then on the flow the would be a vent on the drop and a vent on the rise up to the cylinder, and also put the safety discharge on as diagram, could you see any issues with that

 

[Ric2013]

That’s way different that having a drop and rise / trap before the header thank hence if it boils will have no where to go hence bomb as the drop / rise won’t flow so acts like a trap, trapping the water

The OP's original drawing didn't have a drop and rise before the header tank?

If you look on the flow there’s a safety discharge/ valve and the feed teed into the return at boiler so if does boil the tank will refill with cold and safety will blow the boiling water out

It’s not the best design but will work but normally find it’s noisier as the flow has to cool a bit for it to drop and start the circulation on start up

Yeah, there's an injector tee on the pumped side which should start the gravity cylinder going. Agree it's not a perfect design if the cylinder is to be the primary heat dump (which I disagree with doing anyway).

Also we’re not in Ireland hetas is our solid fuel body

Long version... HETAS has not got the monopoly on competent persons for solid fuel but we all think of HETAS because they have a certain regulatory power and like to pretend only HETAS installers are deemed 'competent persons', but other schemes exist.

The OP has now done a revised drawing in which he asks if there any issues. Yes... the heat leak radiator will airlock unless he fits some kind of autobleed (the Aladdin type will work but then it takes so long to reopen once it has closed, it's not a reliable way of ensuring there is always circulation so the cylinder becomes the main circulation). 2 times 22mm could be argued to be equivalent to 28mm as a vent, but as one is across the drop, it's not necessarily going to be free to vent the boiler if it boils. Safety aside, I'm not convinced the cylinder in that latest sketch will gravity circulate and there is no pump in the system.

I'm going to be honest. It is possible to get gravity circulation where there are drops. I have seen it working. What I'm not sure is whether I have fully understood the mechanism, and I feel a need to set up a test rig to check if I've understood or not. But the one I have seen uses, I think, the gravity circulation of a cold cylinder to kick-start the gravity circulation in a small radiator. I'm not entirely sure it's 100% safe, but as the boiler is a backboiler in a rubbish and inefficient woodburning stove and the owner keeps burning wet wood, I doubt boiling is likely.

 

[ShaunCorbs]

Long version... HETAS has not got the monopoly on competent persons for solid fuel but we all think of HETAS because they have a certain regulatory power and like to pretend only HETAS installers are deemed 'competent persons', but other schemes exist.

True building control will also cert it but op isn’t qualified so no go either way also building control want to see it’s been installed a qualified person

 

[Ric2013]

True building control will also cert it but op isn’t qualified so no go either way also building control want to see it’s been installed a qualified person

I was thinking of OFGEM actually. They tells me they have a solid fuel competent person scheme. In the case of the OP, he could, surely DIY it and notify it to BC, but I'm not convinced he has the knowledge to design the system in a way that BC will deem acceptable.

Out of interest, Shaun, on that Irish Heating and Plumbing Association drawing, just near the vent tee, can you make out what the weird bit that connects the flow and the return together is? Looks like CCTs, but that doesn't make sense to me.

 

[ShaunCorbs]

My guess / thought is a temperature bypass but tbh not the best design as there’s no heat leak once the cylinder is upto temp and not enough pipework losses to stop it overheating / safety valve blowing

I would want a temperature bypass or 2 n/o port valve with a stat on the cylinder to a heat leak the same size as the max stove cap

 

[Ric2013]

I would want a temperature bypass or 2 n/o port valve with a stat on the cylinder to a heat leak the same size as the max stove cap

Agreed. I've lived in a house with a woodburning stove and backboiler. It did a tremendous job of heating the Primatic-type cylinder, but it didn't actually have a heat leak radiator, so the only sensible thing to do was to let the fire go out when the cylinder was hot. The firebox and backboiler were both small so serious overheating was not possible unless you persisted in stoking the firebox once you heard the backboiler kettling, but this also meant that you could only ever really have it alight for 2 hours (4 if you had a bath at half-time)..

It relied on user understanding for safety, which isn't the British way. Italian unvented cylinders with a woodburning firebox largely rely on the same principal: tiny firebox and a dial gauge with a red zone that you try not to let the pointer needle go into, so perhaps Ireland takes the same approach that you need to be competent (in the general sense of the word) to use solid-fuel stoves, whereas in the UK we only need to be competent (in the construction sense of the word) to install them.

Back to your normally open 2-port valve, I think that is probably the best way for this kind of system. Then, if the heat leak rad has to be in an undesirable location (for example if you live in a bungalow), it only gets heated when the pumped circuit fails (in a way, the ideal would be to have the heat leak directly above the stove so when everything else is off, the effect is to heat the room the stove is in as if it were just a plain old stove).