 Is your heater making you sick? Here's how to tell. Your vents look like this. You typically don't have seasonal allergies, but you definitely have them this winter. You rarely open up your windows. According to the EPA, our indoor air quality can be five times more polluted than outside. Here's what to do. Change or clean your filters at least four times a year. Open a window. Yes, it's cold, but if you can, try to get a little ventilation. Try an air purifier. Or limit your heater usage overall. Sure, sometimes you have to, but if you can, try to only use it when you really need it. You'll save some money and get better sleep.