I think I'm right in saying that atmospheric pressure decreases with height. Thus, the air inside the top of a tall chimney is of a lower pressure than that inside the bottom of the chimney. So nature and brickwork can provide an up draught of air at no cost or use of machinery.
In a very small way I wanted to use this principle twice in a house that I was designing for myself in the early 1960s.
In one instance, I ducted outside air beneath floor level to below a fire's grate, controlling its volume with a butterfly valve, also below floor level, allowing nature to cause an up draught for the fire's smoke (aided, of course, by heat generated by the fire itself). To make fire work efficiently a draught is necessary. In a house this arrives generally through ill-fitting doors and windows. So the underfloor method prevents unwanted draughts and stiff necks.
Therefore I designed and built a second chimney right next to the fire's chimney. For this one I also ducted in air beneath the floor from outside to be warmed by the real chimney's heat. This transfer-heated air was directed straight into a bedroom above, controlled there by an adjustable grill.
Openings for the vent pipes outside had to be vermin-proofed with wire mesh.
I sold the house to Francis Bacon, the painter, when I decided that I had cut myself off too severely from metropolitan life. Even a blue tit had decided to roost in my bedroom.
Francis was bewildered by the above chimney innovations and ducts, so invited me to visit and explain them to him. We got on so well that he invited me to stay, but with only one bedroom and an internal balcony, and his boy friend George Dyer in residence, I declined the offer.
But I went there again for lunch of raw kippers, decorated with raw onion rings, with Champagne to drink.
Perhaps not being one of his coterie in any way and not being on the make, we became good friends.
