Not as efficent, particularly if you only need it for a half hour. If you aren't needing the heat, a fire is a big fat waste of time, energy and wood.

You can also use something like this where you can't use a campfire- like a parking lot.
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-IronRaven

When a man dare not speak without malice for fear of giving insult, that is when truth starts to die. Truth is the truest freedom.