I burn wood and came up with an idea to burn hotter with less wood and hold the heat longer.  I changed my firebrick to the heavier and used 2.25 inch brick. I added an extra brick to keep all the hot coals in the center of the fireplace.  It holds the heat longer and burns wood completely, with little to no creosote.  I cleaned my 20 foot chimney and this is all the creosote I got, about a shot glass worth.