Why Cutting the Heat Pump Water Heater Added $31K on a 21-Unit Revere Build
On a 21-unit all-electric Revere MA project, dropping the in-unit heat pump water heater forced envelope upgrades that added $31K net of the equipment savings.
Cutting the heat pump water heater added $31,000 to a Revere multifamily project. On a 21-unit all-electric new construction building, the design using an in-unit heat pump water heater priced out cheaper than the electric resistance version, not more expensive. The instinct to strip the fancier equipment made the building cost more, not less. The reason lives in the energy model, not the plumbing bid.
The Real Numbers
The project is 21 units, all-electric, new construction in Revere, Massachusetts. Two water heating approaches were priced against each other. One put an in-unit heat pump water heater in every apartment. The other used a standard electric resistance tank.
The heat pump water heater design came out $1 per square foot cheaper than the electric resistance design, across the whole building. That is the opposite of what the equipment tags say. A heat pump water heater costs more than a resistance tank as a piece of hardware, so on the plumbing line alone, the resistance option looks like the savings.
Cutting the heat pump water heater to capture that saving added $31,000 to the project. The line item that looked cheaper made the building more expensive. The equipment bid and the building cost pointed in opposite directions.
The Envelope Penalty
A heat pump water heater is roughly three times as efficient as an electric resistance tank at making hot water. In the energy model, that efficiency is worth real points toward the code target. The building gets credit for it whether anyone thinks of it as an envelope measure or not.
Take the heat pump water heater out and those points disappear. The building still has to hit the same code target, so the points have to come back from somewhere else. Somewhere else means the envelope. More insulation, better air sealing, or better windows, until the model climbs back to where it was.
That buy-back is not free. On this project the envelope upgrades needed to replace the lost water heating efficiency cost more than the money saved by switching to the cheaper tank. The net of the two moves was $31,000 in the wrong direction. You saved on the water heater and spent more than that saving to pass code without it.
This is why water heating cannot be priced in isolation on an all-electric building. The domestic hot water choice and the envelope are two ends of the same energy budget. Change one and the model rebalances the other, and the rebalance shows up as a cost nobody attached to the water heater decision.
When Cutting the Heat Pump Water Heater Still Makes Sense
The math on this project favored keeping the heat pump water heater, but that is not a universal rule. There are buildings where the resistance tank is the right call, and the way to know is to model the specific project.
When the envelope has room to spare. If the building is already clearing its target with margin, dropping the water heater efficiency may not force any envelope upgrade at all. With no buy-back to pay for, the cheaper tank stays cheaper.
When space and noise make in-unit units hard. A heat pump water heater needs air volume and makes noise and cold exhaust. In tight units or specific layouts, the resistance tank avoids design compromises that carry their own cost.
When a central plant changes the comparison. In-unit is only one way to do heat pump water heating. A central heat pump plant shifts the equipment, the distribution, and the maintenance model, and it can beat both in-unit options on the right building.
When maintenance capacity is the constraint. A heat pump water heater in every unit is a piece of mechanical equipment in every unit. On a building where the owner has no appetite to service that, the simpler tank has a value the energy model does not score.
The Decision Framework
The takeaway from Revere is not that heat pump water heaters always win. It is that the cheaper piece of equipment is not always the cheaper building. On an all-electric project the water heater is an energy measure, and cutting it sends a bill to the envelope that can be larger than the saving.
Our own read on this one is that the better envelope is worth having anyway, because it buys the building out of a maintenance-heavy water heater in every unit for the life of the equipment. That is a judgment call, and yours might land differently. What is not a judgment call is that the decision has to be modeled as a pair, water heater and envelope together, because that 21-unit building told the opposite story from the equipment bids. The only way to know which way yours points is to run both and compare the net.