I've been using mostly kerosene heaters for my snakes for the last two years & haven't seen any ill effects. I also us them fairly often in my house.
I use the large, round ones. Convection heaters, I think they're called. They put out aprox. 25,000 BTUs, which can heat a decent size room, easily.
Today's heaters have come a long way from the ones of several years ago. They are pretty much fume-free if the wick is good and adjusted right. The only time you can smell fumes is if you let them run out of kerosene, which also damages the wick if done very often.
Its important to put a pan full of water on them so they don't dry the air out too much, causing humidity problems within the cages.
Another thing to remember is to burn regular kerosene and not the slightly cheaper farm/untaxed/undyed kero. The cheaper kero gives off more fumes.
As with anything/everything else, there's always bound to be an opposing view. I'm just speaking from experience, not theory. But then again, the fumes could have made me crazy.
Take care!
Mike
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It is said that 1 out of every 4 people are mentally unbalanced. Think of your 3 closest friends, if they're normal, then it's you.