Presents a working document for building professionals. Outlines a number of appropriate assessment procedures and strategies for optimising the process of retrofitting/enhancement of heating and cooling systems in commercial premises in the UK. Also provides guidance through a logical sequence of steps starting with consideration of the retrofit options consistent with the client's requirements. Draws up a checklist for designers to cover the documentation required on existing systems and building information relating to construction, Highlights the major constraints on retrofitting. Covers retrofit options for space heating and cooling systems and documents their relative advantages and drawbacks. Recommends a retrofitting evaluation procedure suitable for a rapid 'first glance' assessment, followed by a more in-depth analysis.