You can keep the bathroom fan running all the time, but it’s not recommended. There are several reasons why you would not want the fan running all night long. First of all, the fan might start developing problems from running all the time.
It’s also a fire hazard as exhaust fans can cause fire by overheating. Here’s what happens when you let the exhaust fan run for too long. The motor gets overheated, and the dust or lint stuck in the vents can catch fire.
The temperature of the motor can be up to 250 degrees. This can be alarming regardless of how small the motor of the fan is. One way to proactively prevent fire is to clean the fan grilles periodically.
There was an incident in Ohio where a building burnt down, and on the investigation, an exhaust fan was found to be the problem. This could be an isolated incident but still calls for caution.
In any case, you would be running the fan all night to consume more energy. Even with an energy-efficient fan, you could be looking at increased costs over time. Therefore, it’s best not to leave the exhaust fan on in the bathroom for extensive periods.