Yezd has a much warmer "hot season" than Isphahan, and the heat is much more trying and of longer duration. The houses are essentially summer houses. The winters being shorter and much less severe, little attention is paid to the comforts necessary for cold weather, but everything is considered which will add to the coolness and airiness of the houses.
As a traveller approaches Yezd he cannot fail to be struck by the number of tall "chimneys" rising from the city, and he almost fancies he is approaching some large manufacturing town, and speculates perhaps as to the nature of the manufactures possible in such a sandy city of the desert. But as he draws nearer he sees there is no smoke rising from these "chimneys," and so concludes that, after all, they are not for manufacturing purposes. What, then, is the purpose of all those tall, square, chimney-like buildings, appearing from the roofs of nearly all the dwelling-places of Yezd? They are air shafts, built with the hope of bringing a little cool air into the houses during the hot season, when the atmosphere below is so stifling that it seems impossible to breathe. These structures are called "bâd geers," or "wind-catchers." There was a very large one connected with the house in which we lived in Yezd, and even on the hottest days, some air was always to be felt coming from the "bâd geer." It was so arranged in our house that after the air had been caught and brought down by means of the chimney, it passed over a "hoze" (tank of water), and in this way was cooled before circulating through the house. Another aid to bearing the heat in Yezd is the custom of spending the middle part of the day underground in cellars.
Some of these cellars are quite palatial, the walls and floors being made from the famous Yezd marble, which closely resembles alabaster. One such I remember very well: it was a room about 40 feet by 30 feet, very lofty, and lit from the top by windows on a level with the ground above. In the centre of this room was a "hoze" (water tank), of which the Persians are so fond, and rising from the water was a fountain capable of playing to the height of 30 feet; a large bowl turned upside down had been fixed on the ceiling to catch the spray and prevent it from becoming damp. Here the inmates of the house took their mid-day siesta, and very charmingly cool it was compared to the upstairs world. Some cellars are not at all healthy, and, if slept in during the day, the sleepers are very liable to contract malaria or some other fever. When dry and well ventilated no harm seems to come from this custom of retiring underground during the great heat of the day, and certainly a good cellar is a great boon to a European, and a great blessing when the thermometer registers 110 in the shade upstairs, while in the cellar it rarely goes above 86 or 90 degrees.