Heating systems in diesel multiple unit (DMU) trains often use additional mechanical and/or electrical auxiliary power, increasing fuel consumption, while waste heat is available from the diesel engine. Delivery of waste heat for heating of multiple carriages is analysed as realized in DR1 and D1 series trains, in light of the current standards of passenger comfort and in-depth testing of DR1B trains. A new hybrid hot air and electrical heating system and its control algorithm is reviewed for modernized DR1AC trains of Latvian railways, capable of extracting waste heat from three different sources and supplemented by two additional sources in case of shortage, for full conformance to EN 14750-1 standard. Results of factory testing are included.