When the weather is hot, and the inside of the house is cold, why do droplets of water form on the windows? Do they form on the outside or inside of the windows? Thanks.
Water droplets form because of condensation. Here is a site that that talks about that. Actually, I have seen condensation both ways. That is, in the winter time with gas heat (produces CO2 and H2O) and very cold tempertures outside, the picture windows (not insultated) get cold enough on the inside of the house to actually freeze the water droplets on the inside of the window. If the humidity is high outside and the temperature is not all that high, then a cool house can condense water vapor that is on the outside of the window. http://www.harveyind.com/homeowner/windows_doors/condensation_causes_cures.asp
When the weather is hot outside and the inside of the house is cold, water droplets can form on the windows due to a phenomenon called condensation. Condensation occurs when warm, moist air comes into contact with a surface that is colder than the dew point temperature of the air. In this case, the cold surface of the window cools down the warmer air inside the house, causing the water vapor in the air to transform into liquid water droplets.
Whether the droplets form on the inside or outside of the windows depends on various factors such as the temperature, humidity, and insulation of the windows. In the example you mentioned during the winter time, when the temperature outside is very cold and the gas heating system produces carbon dioxide (CO2) and water vapor (H2O), the inside of the windows can get cold enough to freeze the water droplets on the inside of the window.
On the other hand, if the humidity is high outside and the temperature is not extremely hot, a cool house can cause water vapor from the outside air to condense on the outside surface of the window.
To further understand the causes and remedies of condensation on windows, you can refer to the website mentioned: http://www.harveyind.com/homeowner/windows_doors/condensation_causes_cures.asp.