Installing a dedicated domestic hot water (DHW) plant is a common energy conservation measure (ECM) in the New York City multifamily market. According to Local Law 87 data, approximately 80% of the audited multifamily floor area uses steam heating boilers to produce domestic hot water. A recent SWA analysis of data from steam buildings with tankless coils that implemented this ECM suggests that auditors may want to think twice about recommending this measure widely.
Two unsupported arguments are typically made in favor of installing a dedicated DHW system.
- A new condensing boiler or water heater (we will just say “water heater” here for simplicity and to distinguish the dedicated system from the heating boiler) will operate at a very high efficiency.
- Scotch marine steam boilers are inherently inefficient and are plagued with high standby losses. Large Scotch marine boilers fire to meet small DHW loads, and correctly sizing a new dedicated water heater will eliminate short cycling.