Improving the energy efficiency of low-power solid fuel hot water boilers Parviz Khujaev, Turobcul Kholmuratov, Jamshed Ismatullozoda Ismatullo and Rajabali Shakirov E3S Web of Conf., 452 (2023) 04008 Published online: 30 November 2023 DOI: 10.1051/e3sconf/202345204008