Question: De Dietrich Remeha, is one of Europe's biggest manufacturers and distributors of domestic and commercial water and space heating systems, in July 2009, when heavily laden with debt, which of Europe's largest manufacturers and distributors of domestic and commercial water and space heating systems, agreed to merge with them? 
Sentence (from "District heating"): District heating plants can provide higher efficiencies and better pollution control than localized boilers.
Relevant evidence: No