The Riverside Company, a global private investor focused on the smaller end of the middle market, completed the investment in Mainstream Electric, a provider of residential HVAC installation and repair, plumbing, electrical, excavation and drain services in the Greater Spokane, Washington, and Coeur d’Alene, Idaho, markets. Financial terms were not disclosed. "We are thrilled to work with Todd & Elaine Damschen, Mainstream’s management team and its expert technicians who have provided first-class services since 2000. During our partnership, we plan to make strategic investments across the various service lines, promote cross-selling and grow the newly introduced sewer and drains business," Meranee Phing, Riverside Senior Partner.