Gravity circulation how powerful

[tamz]

what happens if the tank boils for 501 hours ? I will continue to give the same advice irrespective of hetas or any one else for that matter

I totally agree with you Transam

What Goldspoon needs to realise is there is a difference between what is permitted and what is best practice.
Most solid fuels will boil over at some point, depends how big you like the fire. After a few years it may well have held boiling water for more than 500 hours. I have know solid fuel stoves and cookers to boil over on an almost daily basis when no rads. I even still take the expansion through the roof with a swan neck if no rads. Not because i have always done it that way but because i know it will boil regularly and all that steam in the attic is not good for the building.
As an F&E tank is more or less a fit and forget item who is going to have it changed every few years? Who can say how many hours of boiling water it has held and when it needs changing?
For the sake of a few quid, I will continue to sleep easy in my bed and fit galvi or fibreglass and know my customers can sleep easy in their beds below, no matter what Hetas or anyone else say.

Some seem to think solid fuel and woodburners are a new idea?? I've done it since the 70's when i was fitting up to 5 a week and was taught the dark art from men who had forgot more than most will know. The courses at the time were run by the coal board (SFAS) and they were good in depth week long courses with written exams not ABCD's and an open book to look up the answers.
If the Hetas appreciation one has a 33 - 50% failure rate there must be some amount of clueless halfwits going through it.

 

[Onetap]

He says they will get hot and therefore will act as heat sinks anyway - just choose your rad and make sure the valves cannot be closed. I do not know - my knowledge of convection suggests that cold water falls through lighter hot water (e.g. hot rises). however if this is the case then surely the DROP I mentioned earlier has cold at the bottom and hot at the top - so why would any kind of convection take place?

The circulation is caused by the pressure difference across the boiler.
The pressure difference is ;

(Dreturn - Dhot ) x height x g, where

D is the density of the water and g is the gravitational constant.

The hot water is less dense than the cold water. You can calculate the pressure difference available at the design temperatures and the pipe sizes required to achieve the design flow rate, excatly as you might size a pumped system.

The problem is that the available pressure difference is tiny ( compared with that produced by a pump)_ and you have to use huge pipes (1", 1 1/2" or 2" typically) to get the flow rate required. Most heating systems used to work by gravity circulation, it can be made to work.


Your system won't circulate very well because the flow and return are from & to the thermal store, so the height available is very small (18"?). You will get some gravity circulation, but not much. It would work better if there was a return pipe going back to the boiler on the floor below; it would be possible to have a normally open zone valve on this pipe so it only opened in the event of a power failure.

The heat dump radiator is intended to dissipate heat from the system, it will not necessarily prevent it boiling.

 

[mysteryman]

Someone gave us a short list of professional and trade bodies. There are far too many of these.

What the trade needs is a professional body such as the British Medical Association or the Law Society, with proper legal powers over its members, who would not be allowed to work if suspended.

This would also lead to an improvement in the staus and kudos of our work.

 

[DeltaT]

what happens if the tank boils for 501 hours ? I will continue to give the same advice irrespective of hetas or any one else for that matter

I totally agree with you Transam

What Goldspoon needs to realise is there is a difference between what is permitted and what is best practice.
Most solid fuels will boil over at some point, depends how big you like the fire. After a few years it may well have held boiling water for more than 500 hours. I have know solid fuel stoves and cookers to boil over on an almost daily basis when no rads. I even still take the expansion through the roof with a swan neck if no rads. Not because i have always done it that way but because i know it will boil regularly and all that steam in the attic is not good for the building.
As an F&E tank is more or less a fit and forget item who is going to have it changed every few years? Who can say how many hours of boiling water it has held and when it needs changing?
For the sake of a few quid, I will continue to sleep easy in my bed and fit galvi or fibreglass and know my customers can sleep easy in their beds below, no matter what Hetas or anyone else say.

Some seem to think solid fuel and woodburners are a new idea?? I've done it since the 70's when i was fitting up to 5 a week and was taught the dark art from men who had forgot more than most will know. The courses at the time were run by the coal board (SFAS) and they were good in depth week long courses with written exams not ABCD's and an open book to look up the answers.
If the Hetas appreciation one has a 33 - 50% failure rate there must be some amount of clueless halfwits going through it.

I completely agree with you Tamz, how can someone with such limited knowledge be qualified in anything to do with Solid Fuel Heating?? It's a sham & this trade is now full of clueless morons like this!!
CC/CCCs!!!!

 

[DeltaT]

Quite right, there is far too much rudeness and too many-clever dick replies to valid points on this site.

If a gravity system is well laid out, there can be some short lengths of pipe going apparently in the wrong direction. The receiving vessel needs to be higher than the source, and, as long as it starts in the correct direction, it can work.

would this be thermal centres ?? eg as a rule of thumb the thermal centre of a boiler should be a minimumn of 3 feet below the thermal centre of the cylinder ( centre of coil connections ) for gravity circulation to work satisfactory ?? However bit before my time but I used to work with a fella long since passed away who used to install gravity primary circuits were the thermal centres were virtually non existent , particuly in bungalows he refered to it as inducing a syphon action ???? the return to the cylinder would step up from under the floor into the return this step up distance was critical ??

On another point I have seen drops to rads work on gravity be it they were not designed to do so ! Also can we not be a little more civil to some O.P's fella asked a question in a decent way , educate, help we all need it at times !!

All the above systems were still installed in the late 60s when I started my time. In fact the old boys I worked with could show you how to install gravity systems with their eyes closed!! Things like that are learned by apprentices, not on some mickey mouse course!!

 

[Onetap]

I completely agree with you Tamz, how can someone with such limited knowledge be qualified in anything to do with Solid Fuel Heating?? It's a sham & this trade is now full of clueless morons like this!!
CC/CCCs!!!!

Simple; not all solid fuel systems are wet systems. It seems he could probably install stoves, fires and flues competently. If he has a wet job, he would probably employ a competent subby to do the pipework for him.

I'd guess it was an opportunity for Dick to slag off someone for not being a TSHW like himself and he couldn't let it pass.

Have you let the WRAS know how wrong their engineers are about the gas porosity of MDPE pipes yet, Dick?

 

[doitall]

Question is: As long as the TRV's on the upstairs rads are open will they (or some of them) get hot via convection and dissipate heat? Note that for this discussion the main rads flow and return 22's DROP from the store and go under the floorboards before getting to rads via last bit of 15mm - drop is approx. 24" for return and 36" for flow. He says they will get hot and therefore will act as heat sinks anyway

Think about that one. How can the heat travel DOWN by convection? Your collegue is not sounding too clever is he?


You have made a big bloomer there Tamz.

Hot water will rise, and provided you have a vertical start-off pipe, it will force a gravity circuit, and the flow will continue down.

In the good old days when plumbers knew what they were doing, they would take the flow pipe as high as possible, more often than not the loft, where you would have a vent pipe, and drop back down through the building, to pick up the cylinder and radiator returns.

One off the big problems with gravity circuits, was actually stopping unwanted circulation.

 

[tamz]

Question is: As long as the TRV's on the upstairs rads are open will they (or some of them) get hot via convection and dissipate heat? Note that for this discussion the main rads flow and return 22's DROP from the store and go under the floorboards before getting to rads via last bit of 15mm - drop is approx. 24" for return and 36" for flow. He says they will get hot and therefore will act as heat sinks anyway

You have made a big bloomer there Tamz.

Don't think so.

 

[doitall]

Agreed if both drop from the store.

But that depends how far apart the flow and return connection is.

A simple modification would be to raise the flow from the store a couple of feet, before dropping.

That also assumes there's no check or zone valves.

I haven't read all the thread and have no intentions of doing so, so may have missed a point or two.

To save an argument, the boiler needs a heat sink, and as far as I know, most solid fuel boilers insist on one.