f 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.

Pipes for the first floor should he large. Those for the upper rooms,
having a longer vertical range, may be smaller. All the pipes should
be double, with an inch air space between, as a protection against
fire. Asbestos paper on a single pipe is not regarded as a sufficient
precaution, as it is easily torn and quickly wears out.

REGISTERS

There are arguments in favor of side-wall registers. They save floor
space and obviate some dust. On the other hand, they are not quite so
effective in heating as the other sort, since the pipes for floor
registers may be of larger diameter and as a rule require fewer bends.
Each register should have a separate pipe from the furnace. Where
direct heat is not desired, a register opening in the ceiling of a
downstairs room will sometimes carry enough heat to the upper chamber
to make it comfortable for sleeping purposes.

Since furnace efficiency is largely dependent upon air control, a
strong wind sometimes makes it difficult to heat portions of the house.
To meet this emergency there is a combination hot-air and hot-water
heater which supplies radiators on the upper floors, or elsewhere if
desired. The additional cost is practically all in the installation,
as the same fire furnishes both forms of heat.

For an eight-room house or smaller, a first-class steel-plate furnace,
securely sealed against the escape of gas and smoke, costs free on
board about $150. Each two rooms additional r