A free mod for Valheim, by TheSxW.
Custom Fireplace and Smelter (CFaS) is a mod for Valheim, that allows you to change the default settings of the game's fireplaces and smelters. You can set the default values to anything you want, including the amount of fuel and the amount of time it takes for a fire to burn, the temperature of the fire, the type of fuel, the number of burners, the dimensions of the fireplace, the number of chimneys, and the location of the fire.
The description of the object that is being set in the CFaS mod will be written to the configuration file, which is found in the application's data directory.