Design Envelope Vertical-In-Line Retrofit allows building owners to replace the moving parts of an installed Armstrong constant-speed pump while retaining the pump casing, insulation, and piping. Owners of constant-speed pumps can save up to 70 percent on energy costs by upgrading to variable speed. Design Envelope solutions do not require differential-pressure sensors, wall-mounted drives, or additional wiring, and because casings are reused, there is no need for a pressure test after installation.