The deal includes the right to acquire the remaining share capital of the business over the next four years.
Econergy is a developer of biomass heating systems, which it sells, designs, installs and maintains for individual domestic properties, business and public sector customers. It also provides community solutions in the form of district heating schemes.
The company’s turnover for the year ending June 2008 was £5m.
The deal complements British Gas’ acquisitions in 2008 of Solar Technologies Group and Semplice Energy, and technology partnerships it has formed with Baxi, Disenco and vPhase.