Gas / Wood 'duel fuel' radiators

[shandy]

Hi,

We currently have a new gas CH system.

I am getting a multi fuel stove fitted and have decided (alomst) to go for a large stove which will also heat the radiators to try to save on the gas bill!

As it is not a usual situation can anyone confirm that this will be a relatively standard operation (running both systems alternatively) with no 'hidden costs.'

My plumber states it is fairly straight forward to do but I wanted a second opinion.

Thanks

Colin

 

[Nixt]

They can work on the same system but it will depend on the gas CH arrangement eg. it would need to be 'open vent', may need to be be coupled through a neutraliser and provide for dissipation circuit of residual heat from solid fuel etc etc... However the cost per kW of any smokeless coal or wood will exceed the cost of mains gas (in a modern boiler), unless of course you have access to free wood.

 

[shandy]

Nixt, thanks for that.

I have a fair amount of wood for starters and plan to obtain it for free thereafter!

Any idea of the approx cost of this operation. I hear the neutraliser can be pricey.

Thanks again

 

[Nixt]

First you will need to establish that the project is feasible in terms of the level of pipework to be disturbed/exposed and your current gas fired system. For that you will need an installer who has a full knowledge of systems and their design and not a 'combi boiler only fitter' (no offence to them). From there they can give you a cost which will depend on the above. Neutralisers I believe are £200-300 to buy.

 

[simond]

If you start extracting heat from a wood burning stove for central heating there are some unexpected drawbacks.

The main one is that the normally near-complete combustion process of the wood is adversely affected by your heating water lowering the temperature in the stove and significant quantities of tar are produced.

This will quickly cause the stove linings - including the glass - to be coated and more importantly the flue will need to be far more regularly swept and the chances of a chimney fire are greatly increased.

Not a good idea really. Why not just use the heat from the stove to heat the house in the vicinity?

 

[Nixt]

This 'cold water corrosion' can be limited by installing high and low stats to the F/R on the wet back stove so that the pump only operates when return temp permits. Otherwise pump is stopped allowing heat build up.

 

[shandy]

Thanks for all feedback, I will show this to my installer

Re: pipework levels - My installer has not done this type of job too many times I believe.

Could you recommend how I could find someone who could give me as second opinion on this to ensure it will work?

Simond - Basically, it seemed a good idea in theory. We were fitting a stove anyway, why not spend more in the initial outlay to heat the rads we have about 20!) so hopefully save some cash long term on running costs. Also I live in Aberdeen so wood is plentiful and I approve of not using fossil fuels if at all possible.

I will get my heating engineer to look implement whatever is necessary to enable the whole system to run efficiently.

All in all is this an achievable project or should I leave alone bearing in mind I have a brand new condensing combi?? But my wood is 'free'!

Ta

 

[Nixt]

Didn't realise it was a combi - a wet back wood burning stove is not compatible with a combi boiler. Two totally separated systems will have to be created. The only way any sealed system boiler can feed the same primary system is through multi-coil thermal store. All uncontrolled solid fuel systems must be open vent.

 

[JohnD]

you might consider a hot cylinder. It is possible to use a combi to heat a cylinder although it isn't usually done. Can be handy if you have e.g. a shower, and a separate bathroom with a bath, as it gives you the ability to deliver a large amount of hot water more quickly than a combi can do on its own. On the other hand, if you have a cylinder, you might ask yourself it ift wouldn't be simpler to just have a system boiler.

It is possible to have a cylinder with two coils (e.g. one from a boiler and one from a wood stove, but this is also unusual.

I used to live in a place with a multifuel stove that had gravity flow to a cylinder (otherwise heated by immersion). It seemed very slow to heat, but it was effectively "free" if I had been using the stove that evening, or the night before. the stove was also slow to heat the main room, though it chucked out a great deal of heat once it had got going.