Rumford on Chimney Pots

Buckley Rumford Fireplaces
Rumford on Chimney Pots
Essay IV, on Chimney Fire-places - 1796

"Various mechanical contrivances have been imagined for preventing the wind from blowing down chimneys, and many of them have been found to be useful; there are, however, many of these inventions, which, though they prevent the wind from blowing down the chimney, are so ill-contrived on other accounts as to obstruct the ascent of the smoke, and do more harm than good.

Of this description are all those chimney-pots with flat horizontal plates or roofs placed upon supporters just above the opening of the pot; and most of the caps which turn with the wind are not much better. - One of the most simple contrivances that can be made use of, and which in most cases will be found to answer the purpose intended as well or better than more complicated machinery, is to cover the top of the chimney with a hollow truncated pyramid or cone, the diameter of which above, or opening for the passage of the smoke, is about 10 or l 1 inches. - This pyramid, or cone (for either will answer), - should be of earthenware or of cast-iron; - its perpendicular height may be equal to the diameter of its opening above, and the diameter of its opening below equal to three times its height. - It should be placed upon the top of the chimney, and it may be contrived so as to make a handsome finish to the brick-work. - Where several flues come out near each other, or in the same stack of chimneys, the form of a pyramid will be better than that of a cone for these covers.

The intention of this contrivance is, that the winds and eddies which strike against the oblique surface of these covers may be reflected upwards, instead of blowing down the chimney. - The invention is by no means new, but it has not hitherto been often put in practice. - As often as I have seen it tried, it has been found to be of use; I cannot say, however, that I was ever obliged to have recourse to it, or to any similar contrivance; and if I forbear to enlarge upon the subject of these inventions, it is because I am persuaded that when chimneys are properly constructed in the neighbourhood of the fireplace, little more will be necessary to be done at the top of the chimney than to leave it open."