Hi, a difficult question, and one that it is difficult to be accurate on despite what other people claim for their products.
Wood has a relatively low calorific value, 1kg of dry wood is about 4.5kW as opposed to coal which is almost double that.
So even if you crammed five 1kg logs in you only have 21kW at best.
It is almost impossible to burn wood slowly, it smoulders and only half burns so at 4kW/ hour you would get 5 hours at best. This applies to every wood stove and cooker ever made.
In practise what happens is the wood burns a bit faster at first and the volatiles/gases are burnt. If you over starve it of oxygen, these just go up the chimney unburnt (tar). The remaining charcoal smoulders away and in the morning there are still glowing embers. Some people say they kept their wood burner going overnight! I say you could put a candle in it and it would still be ‘going’ in the morning, but you would not have generated any heat, probably a bit of tar though.
So it’s always best to run a stove around the mean value, and a little often is the best, 1 log every 45 mins to 1 hour, but if you’re going out, put 2-3 on and turn it down just a fraction. Put 3-4 logs on when you go to bed and again turn it down a fraction, there should be glowing embers in the morning, so that a little pine kindling will catch and you be away in a few minutes.
I hope this helps you understand, I’m trying to be honest. I hear so many claims that don’t stack up.