=The Utilization of the Heat Produced= in the fire-place to warm the air on its way into the room, as in Galton’s and other similar stoves has been already described (page 156).
A larger amount of heat can be obtained out of a given quantity of fuel by cutting off some of the cold air, which rushes through the fire, and carries the half-burnt gases and much of the heat up the chimney. This is effected by having a solid fire-brick bottom to the grate, or by closing up the front of the open chamber under the grate, by means of a close-fitting shield or door. These “Economisers,” as Mr. Teale calls them, appear to answer better than solid fire-brick bottoms, as they do not prevent the ashes falling under the grate.
=The Fuel= burnt in an open fire-place may be either coal or coal-gas. Occasionally coke is also employed. Coke and coal-gas have the advantage over coal, that (1) no smoke is produced. Coal-gas presents the additional advantages, that (2) it can be turned on at any moment, without having to go through a tedious process of lighting the fire; and that (3) the amount of heat can be exactly graduated by regulating the supply of gas. A gas fire is however, as a rule, more expensive than a coal fire.
=Open Gas-stoves= are made in various forms. In the common one, small jets of gas are lit under the grate, which is filled with pieces of asbestos. These become red hot, and radiant heat is emitted. To obtain the greatest value from the heat generated by the combustion of gas, a stove should be chosen in which the heat generated is brought into contact with a large surface of the grate before the products of combustion are allowed to escape to the flue.
Gas stoves which are advertised as not needing a flue, should be avoided. A large amount of carbonic acid is discharged by them into the room, and the sulphurous acid also produced by the combustion of gas is not completely absorbed in the water of condensation which collects in a tray under such stoves.
=Closed Stoves= form the most economical and efficient warmers for rooms of moderate size, and coal, coke, coal-gas or paraffin may be burnt in them.
_The advantages_ rightly claimed for coal stoves of this type are that (1) the amount of fuel consumed is small; (2) by adjusting the damper, combustion may be rendered as slow as desired, so that but little heat is lost by the flue or chimney; and (3) heat radiates from all parts of the stove into the room, and not simply from a small area of fire-front.