To answer the original question I have used a Mr Heater Big Buddy in a large tent (Sleeps 8) several times. It works well unless there is wind, if there is you won't even notice the thing is on. I'll be honest I've never used\needed the co2 sensor because the heater has a low oxygen shut off and that works great. I've even used it inside an RV with a lot of success. In fact once I forgot to vent my tent and the heater kept going out, it was driving me nuts. Once I ventilated the tent the heater stayed on so I can vouch the low oxygen shutoff works great. They are very indoor safe.