evening, i have chimney built in 1930 as its attached to my house, at the builders opening it is around 11 inches but as the flue goes up this narrows to 8. Chimneys built by builders were built properly.
Modern stoves often have a lower POC gas temp, to over come this it may be necessary to pre heat the flue with a paper torch, just to enable draw.
Draw doesnt come from chimney width, it partly has something to do with height, but also on how hot the fire is and how hot one can get the POCs before shutting the doors on stove or closing vents or in case of open fire putting on coal or big logs, the fire should be well established before adding fuel etc etc.
Once the fire is hot enough then POCs will start to rise in turn heating the chimney allowing the cooler POCs to be drawn upwards as cold air rushes into the fire to feed the flames, inturn pushing hot air up the chimney.
Chimneys do not require wind blowing over the top to create draw. its all to do with the science of flames. Get the right temp in your stove and your chimney will draw.
Do not assume your chimney needs a liner. Get your chimney swept and take the advice from your Sweep. He will know what is best for your intended application as he will know the condition of chimney.
Vermiculite is not used when installing a stove, its an insulation material when installing a cast iron victorian style fire. it acts as the back fill behind the fire to fill the gap and insulate it.
Get your chimney swept and keep hold of the certificate issued. your Sweep will often be qualified as HETAS as well as its part of the bigger trade!
