NFR 1.A.4 - Small Combustion comprises combustion systems in the areas Commercial and Institutional (NFR 1.A.4.a), Residential (NFR 1.A.4.b), and Agriculture (NFR 1.A.4.c), along with various mobile sources.

The group of stationary combustion systems in the residential and commercial/institutional sectors is very diverse with regard to installation design and size. It covers a spectrum that includes individual room furnaces for solid fuels with a rated thermal output of approximately 4 kW (e.g. fireplaces, ovens), oil and gas furnaces used to generate room heat and hot water (e.g. central heating boilers), hand-fed and automatically fed wood-burning furnaces in the commercial sector.

Besides stationary combustion, mobile sources are covered, too: From fork lifters in NFR 1.A.4.a ii -Commercial / Institutional: Mobile via lawn mowers in NFR 1.A.4.b ii - Residential: Household and Gardening: Mobile to vehicles and other mobile machinery used in NFR 1.A.4.c ii - Agriculture/Forestry/Fishing: Off-road Vehicles and Other Machinery and the emissions of the German deep sea fishing fleet under NFR 1.A.4.c iii - Agriculture/Forestry/Fishing: National Fishing.