Boiler "Economas" can also be stoked with coal, while avoiding installation of additional fan, which is typically mounted in such cases, due to the lack of oxygen, which leads to boiler to stop burning after 10-30cm of fuel. This can be solved by welding a Ø 32 thread with a valve to the lower door, as shown in the photo. When starting to burn coal, open valve about 1-3mm. After one day, or after about one-third fuel has burned, unscrew valve a little more. Continue unscrewing more and more until after about 4-5 days valve is fully unsrcewed and fuel is burned.