Energy savings can be realized in the production of heating hot water by modularizing the boiler plant. The use of multiple, high-efficiency (88 to 95 percent) boilers allows staged operation of the plant to match the laboratory's heating load. Multiple-boiler plants incorporate relatively small boilers in the range of 500,000 to 1 million BTUH; these are cold-start boilers that do not require continuous operation when there is no load. Each boiler is manifolded in a primary circulation loop with isolation valves to prevent circulation during inoperative periods. The laboratory load is on the secondary loop and, in special instances, a tertiary loop. The energy savings from efficient operation, matched loading, and elimination of standby energy losses range from 40 to 60 percent compared to conventional boiler plants. The modular boiler plant has the added benefits of back-up redundancy in its multiple units and simplified maintenance because any one boiler can be easily taken out of service without disrupting the hot water heating supply.