:* The first lump of clay you use (when starting the forge) will be completely consumed even if it is a 20kg lump.
:* Subsequent use of clay can be taken from a single 20kg lump, however that is inefficient since the lump will become progressively more damaged.
:* The [[quality]] level of a forge is a factor in both how long it stays lit for and how long it takes to heat up items. Example: a 40[[QL]] forge will take 20 minutes to get iron lumps glowing (may also depend depends on quality of lumps).
:* A 70 [[quality]] level forge burns for 115 minutes with 20kg of 44q [[peat]] set to burn in it.
:* If using [[wood scrap]] as [[fuel]] only burn 20[[kg]] at a time. A 40QL forge will last for approximately 40 minutes before it needs refueling (more than 20kg does not seem to effect how long the forge lasts at any QL).