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Considering Heat Pump Hot Water Heaters for Multi-family or Commercial Applications

Heat pump water heaters (HPWH) are not boilers and cannot be sized the same way. Boilers are sized to output peak hourly hot water demand with a small tank to buffer starts and stops.

  • Heat pump costs scale with output capacity
  • Penalty for oversizing significantly more expensive than boilers
  • Design goal: use smallest units possible

HPWHs are most efficient when able to run for 16-20 hours per day, with long run intervals to prevent accelerated compressor wear. To allow HPWHs to operate in ideal conditions, storage becomes critical in system design, being sized to cover peak usage conditions.

Daily usage of a building becomes the primary factor in sizing HPWH systems to ensure the heat pumps can recover the daily hot water demand in 16-20 hours. Tanks are sized by considering building type and their usage patterns to ensure enough hot water is in reserve for peak hourly demands.

Condition 1: Building draw greater than heat pump output

Heat Pump + Storage Draw = Building Usage

Heat pumps are on and output is plumbed in parallel with storage tanks to supply building

Condition 2: Building draw equal to heat pump output

Heat Pump = Building Usage

Heat pumps are on and no hot water is being drawn from tanks.

Condition 3: Building draw less than heat-pump output

Heat Pump = Building Usage + Tank Recovery

Heat pumps are on and output supplies building draw and recovers tanks.

Please refer to our Sizing Forms and contact your local sales representative.