Louis Heinrici of Zwickau, Germany, started building hot air engines in 1876 and these engines were sold into the 1920s when Ernst Heinrici brought out an improved design.
Three types of engine were manufactured.

1. Avertical concentric water cooled engine of 40; 54; 65; 80; 100; 130; 150 or 190 mm diameter piston.
2. A small air cooled engine with a 30 mm piston.
3. A small water cooled engine with a 30 mm piston.

Since these engines were sold over a period of some 40 years it is difficult to date them however Heinrici did bring out a number of improvements. The patent number (DRP), or DRGM number is usually embossed on the cylinder casting.