The Subject of Smokey Chimnies of which I had the honor of conversing with you, at your own house last Eveing, is of so much concern to every individual, as well as to every private family, that too much light cannot be thrown upon it.

And, however difficult it may be, to remedy one of those ills, yet any advances we may be able to make towards removing the inconveniences arising from the other, cannot fail to be favourably received by the public As they are shortly to be favoured with your sentiments, upon that Subject, possibly the following observations which were in fact, occasioned by necessity, and are the result of my own experience may not be altogether undeserving of notice.

When I left London, and went to live in Devonshire in the latter end of the year 1777, It happened to be my lot, to dwell in an old mansion, which had recently been modernised, and had undergone a thorough repair. But as in most old houses in England, the Chimnies, which were perhaps originally built for the purpose of burning wood, though they had been contracted in front, since coal fires came into general use, to the modern size, yet they were still, above, out of sight, extravagantly large. This method of building Chimnies may, perhaps, have answered well enough, while it was the custom to sit with the doors and windows open, but when the customs and manners of the people began to be more polished and refined, when building and Architecture were improved, and they began to conceive the Idea of making their Chambers close, warm, and comfortable, these Chimnies were found to smoak abominably, for want of a sufficient supply of air. This was exactly the case with the house in which I first lived near Exeter, and I was under the necessity of trying every expedient I could think of, to make it habitable.

The first thing I tried, was that method of contracting the Chimnies, by means of Earthen pots, much in use in England, which are made on purpose, and which are put upon the tops of them; but this method by no means answered. I then thought of contracting them below, but as the method of contracting them in front, to the size of a small coal fire Grate, has an unsightly appearance, as it makes a disagreeable blowing like a furnace, and as it is the occasion of consuming a great deal of unnecessary fuel, the heat of which is immediately hurried up the Chimney, I rejected this method and determined to contract them above, a little out of sight. For this purpose, I threw an arch across, and also drew them in at the sides. This had some effect, but as this contourtion was done rather suddenly, and the smoke, by striking against the corners that were thereby occasioned, was apt to recoil, by which means some part of it was thrown out, into the room, I determined to make the contraction more gradually, and therefore run it up at the back where the depth of the chimney would admit of it, and also shelving or sloping, in a conical kind of direction at the sides, as high as a man standing upright could conveniently reach, and by this means, brought the cavity, within the space of about twelve by fourteen or sixteen inches, which I found sufficiently large to admit a boy to go up and down, to sweep the chimnies. This method I found to succeed perfectly well as to curing the chimnies of smoaking, and it had also this good effect of making the rooms considerably warmer; and as this experiment succeeded so well, since the only use of a chimney is to convey away the smoke, I determined to carry it still farther, in order to ascertain, with precision, how much space is absolutely necessary for that purpose, because all the rest that is shut up, must be so much gained in warmth, accordingly I laid a piece of Slate across the remaining aperture, so as to contract the space, above two thirds, leaving about three inches by twelve remaining open; but this space, except when the fire burnt remarkably clear, was scarcely sufficient to carry away the smoke. I therefore enlarged it to half the space, that is, to about six by seven or eight inches, which I fo’nd fully sufficient to carry away the smoke from the largest fires.

When I removed into the Bedford Circus in Exeter, though the house was modern, and almost perfectly new, yet the chimnies were large, in consequence of which almost every room of it smoked. My Predecessor, who was the first inhabitant, had been at great expence in patent Stoves &c but without effect; but by adopting the method I have just now described, I not only cured every chimney of smoking, but my house was remarked for being one of the warmest and most comfortable to live in, of any in that large and opulent City.

The house I now live in, in Philadelphia, I am told, has always had the character of being both cold and smokey; and I was convinced, as soon as I saw the rooms, and examined the chimnies, that it deserved that character; for though the rooms were close, the chimnies were large; and we shall ever find, that if our chimnies are large, our rooms will be cold, even though they should be tolerably close, and tight; because the constant rushing in of the cold air at the cracks, and crevices, and also at every opening of the door will be sufficient to chill the air as fast as it is heated, or to force the heated air up the chimney, but by contracting the chimnies, I have cured it of both these defects.

There was one remarkable circumstance attending the contraction of the chimney, in the front parlour, which deserves to be attended to; which was, that before I applied the cast Iron plate, which I made use of, in stead of Slate, to diminish the space requisite for a chimney sweepers boy to go up and down, the succion, or draught of air, was so great, that it was with difficulty I could shut the door of the room, in so much that I at first thought it was owing to a tightness of the hinges, which I imagined must be remedied, but upon applying the iron plate, by which the space was diminished one half, the door shut to, with the greatest ease. This extra ordinary pressure of the air upon the door of the room, or succion of the chimney, I take to be owing in some measure to the unusual height of the house.

Upon the whole, therefore, this fact seems clearly ascertained, viz that the size, or flue of the chimney, ought always to be proportioned to the tightness and closeness of the room. Some air is undoubtedly necessary to be admitted into the room, in order to carry up the smoke, otherwise, as you justly observed, we might as well expect smoke to rise out of an exhausted receiver; but if the flue is large, and the room is tight, either the smoke will not ascend, in consequence of which your room will be in a constant smother, or else you must admit a greater quantity of air into your room, the consequence of which will be, that the air of your room will be so frequently and so constantly changed, that the warm air, as fast as it is heated, will be hurried away, with the smoke, up the chimney, and of course your room will be constantly cold.

One great advantage attending this method of curing smokey chimnies, is this, that, in the first place, it makes no aukward or unsightly appearance, nothing being to be seen but what is usual to chimnies in common; and in the second place, that it is attended with very little expence a few bricks and mortar, with a plate or covering to the aperture, and a little labour, being all that is requisite. But in this new country where crops of houses may be expected to rise almost as quick as fields of corn, when the principles upon which chimnies ought to be built is thoroughly understood, it is to be hoped, that not only this expence, small as it is, but that all the other inconveniences we have been speaking of, will be avoided, by constructing the flues of the chimnies sufficiently small. From your humble Servant