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Thanks Chris, for that very interesting link.
Thanks too BOO (how ya doing?)
We were given one of these many years ago, as a present, but never used it. Mr C thinks it is too much hassle for too little result. I want to give it a go, so perhaps we will one day.
It's a bit academic actually, as we don't have an open fire at the moment, but we are hoping to move back to a house with an open fire (we miss our open fire).
Thanks again for replies. :o)