So we shall have to decide the question for ourselves. If we err, we can still abuse the dealer, or the architect, or the contractor, for letting us make a mistake.
The hot-air furnace costs least to install. (We leave stoves out of consideration.) It is also supposed to be easiest to manage. That, in a sense, is true. A good furnace will act pretty well even under indifferent direction; a bad one cannot be made much worse by the greatest of stupidity.
However, the average person can run the average furnace with a fair degree of satisfaction to the household, if not to himself. For a house of six to eight rooms the furnace may be considered an efficient means of heating. It requires more fuel than some other apparatus, but there are compensations.
Since ventilation and heating are inevitably associated, the argument that the furnace provides for ventilation is a strong one. If the air is taken from outdoors, passed over the radiating surface into the rooms, and then sent on its way, something like perfect ventilation is assured. If the air is simply taken from the basement--a poor place to go for air--heated, passed through the rooms, returned, and heated over again, we may well pray to be delivered from such "ventilation." The success of the furnace depends not upon ability to keep up a rousing fire but upon a proper regulation of air currents. Many a first-class furnace, properly installed, fails to work satisfactorily because the principle of heating is not understood. Even with the best of knowledge, the air is hard to regulate, and the very principle that gives the furnace its standing as a ventilator must prevent it from being a perfect heater.
Unless some artificial moisture is provided, not only will the air be too dry for comfort and health, but an excessive degree of heat must be attained in order to warm the rooms, thus increasing the consumption of coal. A water pan is usually provided in the furnace, but too often it is neglected.
If any mistake in selection of size is to be made, it should be in favor of excess. Most authorities urge the choice of at least a size above that indicated by the heating area. A chimney with suitable draught is imperative. The furnace should be placed in a central location and should be set sufficiently low to permit the essential rise of the heat ducts. If the basement is low the furnace should be depressed. While the heat conveyors should not ascend directly from the furnace, they should not be carried any farther than necessary in a horizontal position. The velocity of heat is diminished in carrying it horizontally, increased vertically. Crooks and turns add to the friction and decrease heating power. Therefore the pipes should be as short and direct as possible. It is not necessary to carry the register to a window on the farther side of the room, say some authorities, as the warm air rises to the ceiling anyway, and the greater length of carry involves a loss in warmth.