"The object of the art of heating is to secure this required warmth with the greatest economy and efficiency. ...For reasons of health it may be assumed that no system of heating is advisable which does not provide for a constant renewal of the air in the locality warmed, and on this account there is a difficulty in treating as separate... the subjects of heating and ventilation... The object of all heating apparatus is the transference of heat from the fire to the various parts of the building it is intended to warm, and this transfer may be effected by , by conduction or by . An open fire acts by radiation; it warms the air in a room by first warming the walls, floor, ceiling and articles... and these in turn warm the air. Therefore... the air is... less heated than the walls. In many forms of fireplaces fresh air is brought in and passed around the back and sides of the stove before being admitted into the room."