Warner's father, Reese William Sr., founded Warner & Winpigler, a small plumbing and heating company, in 1937 and ran it out of the Warners' Frederick home.

The business became R.W. Warner Plumbing and Heating in the early 1950s, and Bill Warner began working with his father while in high school. He started working full-time in 1959, and the business was incorporated in 1966.

In the following years, Bill Warner bought several smaller companies, including Zigler Brothers' plumbing and heating company, Kaempf & Harris sheet metal plant and Kennedy Fire Protection.

In 1994, the company was divided into four specialized areas, including Warner Construction, R.W. Warner mechanical contracting, Warner Service and Warner Industrial HVAC and plumbing and heating, and Kaempf and Harris sheet metal fabrication and installation.

R.W. Warner was also ranked No. 88 on PM's 2007 Pipe Trades Giants list.