2115. The power of flues depends so much on their construction, the kind of fuel, the roof, mode of glazing, &c., that very little can be affirmed with any degree of certainty on this subject: 3000 cubic feet of air is in general enough for one fire to command in stoves or forcing-houses; and 5000 in lean-to greenhouses. In houses exposed on all sides, 2000 cubic feet is enough in stoves, and 3000 cubic feet for greenhouses. The safest side on which to err is rather to attach too little than too much extent to each fire, as excessive fires generally force through the flues some smoke or mephitic air; and besides produce too much heat at that part of the house where the flue enters.
