With lows dipping into the 30s at night this week, many Iowans have already clicked on their furnaces. MidAmerican Energy spokesman Kevin Waetke says that could be a risky move if the appliance hasn’t been cleaned in a while or checked over for mechanical problems.Waetke says Iowans should hire a professional to look the furnace over and make sure it’s ready for the winter ahead. Furnaces that aren’t venting properly could be pouring toxic gas back into the home, so he says people should also consider investing in a carbon monoxide detector.Waetke says not all carbon monoxide detectors are created equal. He recommends one with an audible alarm and a digital level indicator.The symptoms of carbon monoxide poisoning are similar to the flu and include dizziness, fatigue, headaches, nausea and trouble breathing. Waetke says now is also a good time to have your fireplace and chimney inspected and cleaned by a pro.