Indirect heating is provided by passing air over radiators attached to the ceiling of the basement, thence to the upper rooms. In the "direct-indirect" system the radiators are placed in the partition walls of the rooms they are to heat, the cold air being brought through a duct and, being heated, passing into the rooms. These two systems are economical of space and afford provision for excellent ventilation. They are considerably more expensive, however, than the direct system, which involves exposed radiators.

Radiators are now constructed in many different forms, to fit under windows, in corners, in fireplaces, under cabinets, and so on. Much effort has been directed also toward relieving their painful ugliness, and if of a neat design appropriately colored they need not be a serious blot upon the decorative scheme of a room.

Radiators, in the direct system, should be placed far enough from the walls to permit free circulation over the heating surfaces, and should not be directly covered at the top. Ordinarily there are good reasons for putting them near the more exposed places, such as windows and outer doors. As both steam and hot water furnish a dry heat, provision should be made in every room for evaporation of water.