Page:Steam heating and ventilation (IA steamheatingvent00monrrich).pdf/52

 and then planed off the extensions and re-tested them. They found that with one radiator, which had 43 per cent. more surface in the first condition than in the second, gave only about 17 per cent. more heating effect. This, however, is not exactly a fair comparison on the grounds of extension surface alone, as the radiators had a much more effective proportioning of air-space design with the extensions planed off.

Surface of radiators.—There are other considerations which alter the effectiveness of a radiator besides the design and setting, notably the condition of the surface. Radiators are rarely used with the natural iron surface, but are painted in all possible ways. The nature of the surface has practically no effect on the convected heat, but a very decided effect on the radiant heat; but as the latter is generally less than 35 per cent, of the whole, the effect on the total heat emitted is not so marked. Furthermore, usually only the top and outside surface of one side is painted at all. In general the dark and lustreless paints are the most effective, and may even improve the heating power, while the bright shiny metallic paints may reduce the effect quite decidedly.

But few tests as to the effect of paints have been made. Prof. Carpenter found that two coats of black asphaltum increased the total heating effect by 6 per cent., two coats of white lead 9 per cent., rough bronzing about 6 per cent., while a coat of glossy white paint reduced it by 10 per cent., although the kind of radiator considered is not mentioned. The author found that two coats of ordinary "radiator japan paint" had but little, if any, effect, but in one case, on a 38-inch flue radiator, three coats of gold bronze reduced the heating power by over 12 per cent. This loss was probably due partly to the reduction in radiant heat from the polished surface and also to the fact that the convected heat was somewhat reduced by the heavy coating of paint acting as a non-conductor. This is doubtless sometimes the effect with old radiators which have been painted several times.

Location of radiators.—As before stated, the setting of the radiator has a decided effect on its heat-giving power, and no two conditions can be considered exactly alike in this regard. For direct radiators, the best place to set them is unquestionably under a window. The reason of this is that the greatest leaks of cool air from outside are around the window frames and the greatest loss of heat by radiation is from the glass. There is in