heating in Roman houses
In summer the cool, lofty rooms and the shady garden porticoes of the domus provided welcome relief from the heat and glare; but in winter the same rooms could be uncomfortably cold and dark. Although the chill of mosaic and mortar pavements could doubtless be alleviated with the aid of woven rugs, there was no entirely satisfactory way of heating living-rooms and bedrooms in early-imperial times. The under floor heating systems which were employed in bath-suites were rarely introduced for other kinds of room, except (later) in the colder climes of the northern provinces. Generally householders had to rely on charcoal braziers, a source of heat which would have been unpleasantly smoky, especially in those chambers which were less well ventilated. At the same time the rarity of window glass, not widely available before the first century A.D., created a lighting problem, since openings created to admit light would let out the heat. This is one reason why the older parts of houses had few and small windows. By the time of Seneca the darkness of old-style bathrooms was a matter for comment, but even now the problem of lighting must have remained in many rooms, whether in baths or elsewhere, if the owner could not afford the luxury of window glass and was obliged to employ shutters or hangings to retain the heat. The candelabra and oil lamps used in antiquity would have provided, at best, an inefficient light and would have contributed to the fumes emitted by braziers. Under the circumstances it was often felt appropriate to decorate the walls of badly illuminated rooms with light colour schemes; but there are just as many examples where the heavy polychromy of the murals increased the gloom. Generally speaking, however, amenities improved as time went on. The increasing use of window glass led to a better lit and more efficiently heated style of housing. (Boardman, 1986)