Don't know...Actually, I use another version of (nearly) the same dsign, and never for boiling more than 1/2l of water, with plenty of time on my hands so no hurry (and no watch!)...Mostly, I do not even need boiling water, just "hot". I will probably test it later, when it's colder, and time for "real" food. Drawbacks with tiny wood stove is you have to feed it often, not too much, not too fast. Also, ashes will clog the intake holes if burning time is too long (there is no receptacle, they fall through the grate into the bottom), though I kept it going for 30 or 40 mn without a hitch. A lot depends on the kind of fuel. I found small pine cones the best fuel, one or two at a time!