There are many reasons to invest in building energy optimization efforts. Better and more efficient operation of HVAC equipment can reduce the buildings energy and operational costs significantly. Better efficiency of the heating and cooling infrastructure of a building also leads to more environmentally friendly buildings, something that has become a social prerogative of building owners and operators. Submetering the buildings heating and cooling systems have become increasingly more important, as building owners are both mandated to meter these utilities and have a financial interest in the accuracy of these BTU measurements. Older buildings were not built with BTU meters as metering requirements were added to buildings through increased regulations. Flexim clamp-on ultrasonic meters are the ideal retro-fit meter, but also should receive consideration for new building construction because of the attributes that make Flexim today’s premium BTU meter. Flexim is the meter of choice in large metropolitan areas, where our meters are quietly and reliably delivering 1% performance in small and large commercial buildings, skyscrapers, medical centers, museums, airports, sports complexes, federal institutions and military complexes.