Should we use exhaust fans during wildfire smoke?

If the smokes are near and dense. You should disconnect the electricity and leave your house.

You should not use any ventilation as it may cause soot and dangerous airborne pollutants recirculated.

You should have an emergency evacuation plan with details as what needs to be done around the house and inside such as use of shutters and removing of the combustible material before locking up and powering down.

If the smokes are far you should try to limit to minimum use of AC and ventilation.

In my neighborhood there is public alert text messaging advisory system.

If there is smoke or toxic gas in the air outside your house do not use the exhaust fans. If possible cover the fans to prevent air entering the house via the holes occupied by the fans.

An exhaust fan will remove air from the room where the fan is located and move it outside the house. The air displaced from the room by the fan will ultimately be replaced by outside air drawn into the house by the exhaust fan.

Most houses have gaps around windows, doors, ventilation grills, etc. Fans exhausting air ultimately draw in air through these gaps. If there is smoke outside it will be drawn into the house via the fans through the gaps in the house.

If you must stay in the house during smoking conditions try to seal off the house and plug as many of the gaps as possible.