Do you have a bathroom with a vent that helps you get rid of moisture to protect you against mildew, or a range hood over your stove? These two modes of keeping your home happy and healthy have one thing in common–potential hot and cool air loss. The way these devices work is by sucking up moisture or smelly air to clear a small space, providing greater ventilation and improving the air quality of your home. However, they can work against you when left to their own devices. If you own or operate either of these devices, you want to be sure to run them for only twenty minutes at a time at the most, less if possible. These vents not only remove unwanted moisture and unsightly smells, they are also sucking out the air from your home! That means if you’re running an air conditioner or heater at the time of use, you’re literally blowing the valuable air you are working to treat out of your house. If left for their own devices for up to an hour, the ventilation fans in your kitchen and bathroom can actually remove an entire house worth of air! It sounds bizarre, but this is how the process of diffusion works, undoing all the hard work of your HVAC system. Ventilation fans are a great addition to any home, but be sure to run yours minimally and that the vents are actually closing when they are not in use. Older homes may have kitchen ventilation fans that simply go out through the roof via a pipe, much like a chimney–they can also be a major source of heat loss, letting in cold air in the winter. By keeping track of how you run your ventilation fans, you can work to reduce the cost your heating and cooling system utility bill year round.