I use one similar to the one Nomercy448 posted but only on the coldest of days .... or when my grandson sits with me on a "cold" day ... say below 35F or so. Down my way I consider cold to be below 15F, and of course the humidity and wind play a big role. In a well built box blind a single burner is enough. Now you guys up north that have to endure 0F or colder, I have no clue. If it gets that cold where I hunt in Al. here, I'll probably move to Florida.