I'm still not crazy about non vented stoves. For one thing they produce a LOT of moisture. I know they are not allowed by the building inspector here for houses. Yes most have a safety low o2 shut off themocouples like Little Buddy heaters but the air has to be pretty rare for them to shut off,..and you get a lot of fumes (some people can't smell them or are not bothered by them,..but I can really tell when one is on. A detector is a great idea but not fool proof either,..btw in my 16 x 20 shed I have both,..I use both the non vented and vented to to warm up the place if I'm going to be working out there for a while,..when I get there I open the big doors for a full 5 minutes and sure a lot of heat escapes but I have so much stuff in side (mass) that when I close the doors and the vented heater takes over the heating ,.it warms up fast,..when I open the doors on a very cold day, a LOT of "steam" comes out from the ventless combustion,..OH I wanted to say,..once I only left on the ventless heater (the place is pretty tight) planned on letting it heat up for 3-4 hours before I went out,..a friend came over and we walked in to get him something he wanted to borrow,..BOTH of us came VERY close to passing out,..in a few seconds we were so woosy we hardly made it to the door (windy day and it shut behind me) both of us had a vicious headache for half the day. The point is,..the CO2 alarm never went off!!! Maybe a bad sensor but I got rid of it and got two more,..but Also much more careful. Its true that the non vented one give you a bit more heat as nothing is going up the stack but not worth it if you are going to be THERE. Again , I use the non vented ones to heat up all my junk in the shed,.once its heated I use the other. I think its counter to what I'm out fishing not not breath good air,...