Ive used quite a bit of briquettes last season when I ran out of firewood. I got mine through eBay initially as it was a local joiners who had a hydraulic press for making briquettes out of his waste shavings etc. For subsequent loads I just bought direct.
Obviously his stock wood is kiln dried for joinery so yes, <5% moisture if kept indoors.
I was paying about £50 for 400Kg (a builder’s bag full) which at 5% moisture worked out at something like 2.5p/kWh – there’s pretty much no cheaper fuel available than my own logs or solar. SO I was very happy using it in the furnace.
The problem is the briquettes burn quite hot and fast, they dont linger like a log ember either, so when they’ve burnt out there’s nothing to get the fire going with again – you have to keep on top of them. They also swell when burning so mustnt be over loaded as the can swell and block air supply. That all said, they are great in the boiler furnace because I can burn the nuts out of them and capture all the energy in the thermal store.
You can buy more “refined” versions of briquettes for lots more money (they really are very expensive per kWh and dont make a lot of sense for heavy users) which I guess are made with more care so that they burn a little more log like than compressed joiner’s sawdust.
