The central heater is failing and I'm using a combination of space heaters and the fireplace to warm this house. The fireplace is a pre-fab "typical" mobile home one with a blower. Pretty but too shallow to be of much use in really heating the house. This morning I needed to get rid of a cardboard box and I cut the box into 4" wide strips and burned about a dozen strips at a time. To my delight, the temperature in the house rose from 59 to 65 in about 20 minutes. So.... a question. Is it safe to burn cardboard in a pre-fab fireplace with a metal chimney? I did allow the fire to burn down before throwing more cardboard on as I didn't want to risk getting the chimney too hot. It was so nice getting the house warm fast but I don't want to risk damaging the firebox or chimney. Opinions, anyone?