The American Society of Heating and Ventilating Engineers, the Public Health Service, and the United States Bureau of Mines have cooperated in making intensive investigations to determine the kind of atmosphere best for human beings. Mr. P. E. Fansler in his article "The Problem Faced by the Small Home Owner" in the series "Heating the Small Home"1discusses the results of this investigation. He states:
.... That particular effective temperature at which a maximum number of people feel comfortable is called the "comfort line." While at rest, 97 per cent of people have been found to be comfortable at 640 F. effective temperature. Persons working at various rates are most comfortable at effective temperatures below 64° F. The exact effective temperatures giving maximum comfort for persons working at various rates have not as yet been determined by the research staff, but, from the best data available, they are as follows: At rest, 640 F.; light work, 620 F.; hard work, 6o° F.
So we may take it as a scientifically established fact, that, in the average home, the effective temperature should be 630 or 640. Now, this sounds like a pretty cold atmosphere, as we are used to talking about 700 to 720 as being necessary for human comfort. But the temperatures cited above, as determined standards, are effective temperatures, and not the temperatures read from a common dry-bulb thermometer. What then is "effective temperature?" It is an experimentally determined scale, which is a true index of bodily comfort in all combinations of temperature, humidity and air movement.
.... You will be just as comfortable at a thermometer of 66° F. if there is enough humidity in the atmosphere, as you would be with the thermometer reading 720 F. and the air very dry. As a matter of fact you will be very much better off in the moist temperature and the furniture will not crack in the joints and fall apart; also you can have plants growing in the living and dining rooms - something impossible with the higher temperature-drier air.
In addition to these three major considerations, the research laboratory has set down as important factors, dustiness, bacteria content, odors present, and other injurious substances.
1 In Small Home, September, 1929.