The 44th BImSchV is the German ordinance on medium combustion plants, gas turbines and combustion engine installations. It transposes the European Medium Combustion Plant (MCP) Directive into German law and therefore covers many combined heat and power (CHP) units running on biogas, sewage gas or natural gas, as well as wood-fired boilers and process heating plants. The ordinance sets emission requirements for substances such as nitrogen oxides, carbon monoxide, formaldehyde and total organic carbon, depending on plant type, fuel and rated thermal input. Beyond emission limits, it includes obligations to notify the authority, carry out emission measurements and monitor abatement equipment, for example the reductant dosing of an SCR system. Transitional provisions apply to existing plants, so requirements differ by commissioning date. CHP operators should check fuel, output and year of construction to see which requirements apply, and design the catalyst and any SCR stage accordingly.