Burning too much fatwood in wood stove can clog the stove pipe badly. Dark smoke from fatwood actually forms furry stuff inside stove pipe and pipe must be cleaned running spruce boughs through the sections. Sparkscreens are also easily clogged when using a lot of fatwood. Best to use it only as firestarter in woodstoves.
Has anybody else noticed that?

I also find WetFire good, but better check them before heading out. Also they dry out and hardly burn after that...