On minecraft what can set things on fire on peaceful mode?

Ive been having strange issues lately. My house is wood and being set on fire by a unknown cause. My walls burn down, i got set on fire, some of my ceiling, all in one area, by my furnace. It cant be a Ghast, i have a portal but im on peaceful mode. Cant be the unreleased dragon. Can't be a creeper because they dont cause fires and im also on peaceful mode. And i didn't do it, both times i was upstairs checking my furnaces that are by where the house has been having the fires, and getting stuff out of it. Could it be my furnaces? And downstairs like 5 blocks under, i got a fireplace, and a lava place. I doubt its either of them. Please help me