I'm curious. Is it just my PUP, or do all of them "leak air" at various points on the PUP. I've owned 3 PUPs so far, and everyone had zipper gaps in the canvas where it met the body, door opening gap and small gaps near the roof. I have a Buddy Heater, and the mfg recommends 9 sq inches of ventilation when using the heater. I wish I only had 9" of fresh air instead of what I have...lol.If you go the mr buddy option, get a co detector also. And as steve said, they need some make up air. So you need to crack a window.