You should have windows open when using a fan if you have no air conditioning.
However if you have air conditioning then it's best to use the air conditioning along with the fans and with the windows closed to cool the room or home.
The fans can help circulate the air in the home with the AC going.
If you have no air conditioning then you should open the windows as the heat needs a way to escape and the fans will simply circulate hot air around otherwise.
You should also place a fan in an open window facing outwards so that the fan pushes the hot air out of the room.
Putting a fan in the window does work as the fan pulls in the cool air from the outside and also circulates that cool outside air into and around the room, which then cools down the room.
Also putting a fan pointing outwards in the window can help suck out the hot air in the room and help the room cool down that way as well.
You can make your fan feel like the air conditioner by filling a bowl with some ice cubes and then let the fan blow on the ice.
The air from the fan will circulate through the bowl of ice and pick up the cold temperature of the ice which is then blown on you and will also cool the space down as well.
The evaporating water from the ice that is melted will also add humidity to the air which also helps cool things and yourself down.
You can keep your house cool without opening windows by installing window air conditioners or ventless air conditioners, or use a fan to blow over some ice.
Another thing you can do is use a portable AC unit or install a ductless air conditioner.
Fans do not make a room hotter although fans do not cool a room either.
If the room is hot and you only have fans going then all the fans will do is blow the hot air around the room and only cook yourself or the occupants of the room down.
To cool a room requires the use of air conditioning to remove the heat from the room.
Fans cool people down by displacing the warmer air that is in direct contact with your skin which enhances the rate of convective heat transfer that means you feel cooler.
The moisture in the form of sweat also evaporates on the skin when a fan blows over the skin and also helps to cool our bodies.
It is OK to leave a fan on overnight and sleep with it on.
I leave my fan on overnight and have been doing so for many years to help keep me cool and help me sleep and it's never been an issue.
Sleeping with a fan on all night will cause no harm although if you have an illness such as the flu, cold etc then the fan may make the illness worse but you can't get sick simply from sleeping with a fan on.
Around 20,000 house fires in an 8 year time period have been caused by fans.
Most of those house fires are a result of overheated fans, dirty fans that cause them to overheat, bad cords, lose outlet.
If you're gonna be gone longer than a day it's best to leave the fan off but if you're gone for a short while but are gonna return it's okay to leave the fan on such as for a pet.
If nobody else is in the house or any pets then it's best to unplug the fan as they only cool a person or pet and not the home.
You can leave a fan running 24 hours a day, 7 days a week as long as the fan is in good condition and you keep the fan clean and free of dust, debris etc.
Wash your fan with some water and blow any dust off to keep it in good condition and to prevent the fan from spreading dust around and check the cords etc to ensure they are in good condition.
Also make sure the fans cord fits snugly into the electrical outlet to prevent overheating.
If the fan is in good condition, the cord is in good condition and the outlet is in good condition then there should be no issues running the fan 24 hours a day.
Leaving a fan on all night can cause a fire if the fan is not in good shape or you have a frayed cord etc.
However simply leaving a fan on all night or 24 hours a day is not gonna cause a fire as long as the cords are in good shape, the fan is in good shape etc.
The fan when it gets too hot will shut down to prevent a fire.
A room fan or any fan can catch fire.
However it's rare that a fan catches fire as long as you don't have the cords overloaded, have a good outlet, have a good cord and your electric room fan is in good condition.
As long as you have a good fan, have a good non frayed cord and a good outlet there should be no worry about a fan catching fire.
Fans are meant to run for several hours and even overnight without any issues.
I have my electric fan running all night without any issues.