Does your kitchen get really smoky when you are cooking? This is a problem in some homes, and in some cases, the homeowner might not even be aware why this is happening. Usually, it will be an issue with the kitchen fan exhaust. There are many mistakes that are made when these are installed, whether intentionally or not, but they might be difficult to spot at just a glance.
Your kitchen exhaust fan needs to funnel the air outside of your home through a duct, but some will install a fan with no ductwork at all behind it. This will just be a useless noise-maker. If the duct is venting the exhaust too close to a door or a window, it could be sucked back in into your home.
Some fans are designed as ductless fans, but these are nowhere near as efficient as they should be, so you will be suffering the consequences.
There is a filter in your fan that will need to be replaced periodically, both to improve airflow and to lessen the risk of a fire in a grease-laden filter.