Iowans have turned on their furnaces in recent weeks as the temperatures dropped, but many likely didn’t have those furnaces checked out before doing so. MidAmerican Energy spokesman Mark Reinders says it’s good to have an annual checkup of your heating system.

Most Iowans heat with natural gas, which is colorless and odorless, but a chemical is added to the gas that smells like rotten eggs to alert you if there is a leak. Reinders says if you detect a gas leak, get out of your home immediately and call for help. He says you should not turn on a light or use your cellphone, just leave your home.

Reinders says you should be sure that your furnace filter is clean. He says you don’t have to replace the filter every month, but you should check it to be sure it doesn’t become blocked and lead to a build up of carbon monoxide. Reinders says you should keep any flammable liquids away from natural gas appliances like the furnace and water heater.