The purpose of these studies (Part 1-Part 3) is to investigate residential thermal environments and to get the basic materials for proposing residential thermal indices. The ambient temperature and the temperature at three points on the skin surface of about 50 elderly persons and 40 young persons were measured with a compact thermorecorder and a questionnaire concerning their daily lives was obtained, as well as clo-values and thermal sensation preferences. Their activities were surveyed in summer and winter. The young people, mainly college students, were the control group, and subjects live in six different districts. This first paper reports on the analysis of the effects of residential conditions and air-conditioning control on daily life. The results are as follows : 1) A seasonal difference has been demonstrated in the usage time for air-conditioning. The aged use air conditioners more of the time than college students in winter and less of the time than college students in summer. 2) In summer, for the aged and college students, there has been shown to be a high correlation between the usage time for air-conditioning and degree-day. For high values of degreeday, difference in usage times for the aged and college students is great. 3) A high correlation has been found between clo-values and latitude for aged and college students. Clo-values are generally higher for persons who live in high latitudes and are higher for the aged than for college students. 4) For the aged, a high correlation was noted between clo-value and thermal sensation preference in the daytime in winter. When the aged voted “neutral, ” the clo-value was 1. 8. 5) For the aged, high correlations have been found between fatigue and other aspects of fatigue like health, energy, conditions in hot or cold climates and the aged generally experience weakness in cold climates in summer and winter.