In the northeast, a area gasheater is preferable if it has a vent. The ventless type allows carbon dioxide to enter the room and is not healthy. Note I said CO2 and not CO. But both can give off CO if the heater is prevented from getting sufficient oxygen or not working properly. I have a CO detector in my home in the event the main furnace malfunctions.
I use electric space heaters in my home for safety reasons. I used to have a gas space heater in my basement recreation room and it took me a long time to figure out why I could not easily maintain the pH of the salt water fish tank. The space heater was new but not vented and it would fill the room with carbon dioxide and this in turn would drive down the pH. People can get sick from high levels of CO2. When I first put this ventless spaceheater in service, I did not know of the dangers of high levels of CO2.