I used a 22" tin airtight in a 12'x14' . It kept us warm.I stuffed it using welders gloves tightly full. Tin airtights were only designed to smoulder ,still it was only good for about 4-6 hours . If you run them hot, they would warp the air intake. If you give your partner beer in the evening, he will have to get up to pee and will be able to stoke the fire. GWS doesn't make tin airtights any more.