There is no one temperature and humidity condition at which everyone is comfortable. People are comfortable at a range of temperature and humidity. Research conducted over many years on large numbers of people by the American Society of Heating, Refrigeration, and Air Conditioning Engineers concluded there is a range of combined temperature and humidity that provides comfort to most people. This Comfort Zone Chart shows "Indoor Air Temperature" on the vertical axis, "Relative Humidity" on the horizontal axis, and a shaded area known as the "Comfort Zone".

Notice that most people are comfortable at higher temperatures if there is a lower humidity. As the temperature drops, higher humidity levels are still within the comfort zone. This makes sense if you think about your own experience. Remember being in a hot, dry, desert-like environment and being surprised at how you didn't feel hot? Or being in a humid place where the temperature wasn't that high, but you felt like you were melting? That's the effect of humidity and temperature on human comfort.

Until recently, it was general practice to design for 72° to 75°F and 35% to 40% relative humidity in winter, and 75° to 78°F and 50% to 55% relative humidity in summer. In the interest of energy conservation, in 1974 the Federal Government recommended lowering the winter temperature to 68°F and raising the summer temperature to 80°F for government buildings and encouraged private industry and homeowners to adopt similar practices.