Western Allied Corporation was founded as a Heating, Ventilating and Air Conditioning contractor in December 1960 by Pat Mattson, Hans Sommer, and Harold Waterman. The company moved into its facility in Santa Fe Springs, California in June 1961.

Western Allied Service Company of Southern California, originally a division of Western Allied Corporation, was spun off as a separate company in November of 1976 purely for accounting and administrative purposes.

An office was established in Northern California in 1972 in Belmont, California and moved to its present location in Menlo Park in 1977. This office was managed by Dick DeBrine until his retirement in 1994.

Western Allied Service Company of Northern California was established in 1973 to perform the service and maintenance of the HVAC systems designed and installed by Western Allied Corporation. This company was managed by Dennis Schreck until 1997.

In 2003, the owners of Western Allied made a decision to reorganize the company into Northern and Southern Divisions. Western Allied Corporation of Southern California merged their Service and Construction divisions and continues to exist today representing Western Allied in Southern California.

A new company, Western Allied Mechanical, was formed to operate in the Northern California area. This company consisted of the original Western Allied Northern California construction division, merged with the service division to form a full service HVAC contracting firm specializing in design/build projects.

In 2005, Western Allied Mechanical added another building adjacent to its existing facility to accommodate its growth in Northern California. Western Allied Mechanical Inc., now serves the Northern California area and provides high quality, energy efficient, projects with an emphasis in US Green Building Council (LEED) projects, life science projects, and high efficiency office complexes.

Supported by a Service Division with over thirty technicians available for 24/7 HVAC services.