Improvements in the energy performance of HVAC systems can be obtained by combining thermal storage with decentralized water source heat pumps. Provided proper consideration is given to thermal storage in the original design, a relatively small capital cost premium will result in acceptable payback periods on some projects. The relationship between storage volume and energy consumption is reviewed. Energy consumption is compared on six projects on which thermal storage was a consideration at the design stage. Designs include pressurized and nonpressurized tanks and swimming pool storage. NFPA Standard 13-1978, covering the use of automatic sprinkler systems for heating and air conditioning and related thermal storage, is reviewed.