Hi - I'm about to re-fit my kitchen. It has a recirculating fan at the mo, which is as good as useless (quite old). However, there used to be a solid fuel boiler in the kitchen, with a chimney, which is blocked up now and you wouldn't know it was there. If I were to place the hob under the spot where I know the chimney is, could an extractor make use of the chimney to take the air away? Rather than fit a pipe to the outside wall?
