Now that the weather is getting colder here, but it still isnt that cold, there are always problems with having the windows open or closed. Some people are colder than others. Who does the halochah go by, the person who is cold or the person who is hot?
In the spring or autumn–such as in the current season–no side of a dispute on opening/closing windows has the immediate upper hand. However, if there is somebody who is liable to become sick, whereas for others the question is only a matter of comform/discomfort, the person liable to become sick has the upper hand.
In the summer or winter, there is a general consensus that the window should be closed (in the winter) or open (in the summer, where there is no air conditioner), respectively.
Those who share a room, a bus, and so on, in the winter, do so knowing that the window will in all likelihood be closed; those who share a room in the summer do so knowing that the window will be open. Exceptions to the rule would be an exceptionally hot winter’s day, or an exceptionally cold summer’s day (the latter is very rare), but in general, whoever wishes to enforce the norm for the time has the upper hand.
Chazon Ish (Choshen Mishpat 13:11) adds that when a practice is generally accepted as normal, a person cannot prevent it, even if he claims that he is liable to become sick. Therefore, in the winter the window can be closed even against a claim of becoming sick, and in the summer it can likewise be opened.
In spring or autumn, there is no consensus, and no party automatically has the upper hand, unless weather conditions are extreme. However, if somebody is particularly sensitive, and is liable to be sick, he would have the upper hand on his companions.
This principle is extracted from the Gemara, which discusses a neighbor that has a practice which is disturbing to his sensitive neighbor (a doctor used to let blood, a practice that attracted crows, which disturbed Rav Yosef, his neighbor, who was sensitive to the crows). Accoridng to the Gemara, the sensitive neighbor has the right to demand that his neighbor refrain from the disturbing practice. This is ruled by Shulchan Aruch (Choshen Mishpat 155:39), the Rema adding that the same applies to any significant damage that a person “cannot bear.”
Thus, if there is no clear consensus based on the time of the year, a person is liable to become sick will have the upper hand.
In general, it is of course advisable to reach a compromise, and try to ensure that all parties are appeased.