Multifamily Water Heater Strategy: Unit-by-Unit vs. Central Boiler Systems

For any multi-family Addison property beyond a duplex, the water heater strategy question comes up eventually — usually when the original heaters start failing.

Two paths, real tradeoffs.

Unit-by-unit tank heaters

Each unit has its own 40- or 50-gallon tank. Standard in most 1970s–90s Addison multifamily construction.

Pros:

• Each unit meters and pays for its own hot water
• Failure of one unit's heater affects only that unit
• Simple retrofit / replacement
• No large mechanical room needed

Cons:

• Many failure points to manage
• Each unit needs T&P testing, expansion tanks, code compliance
• 40-year-old buildings have tanks in every unit failing on staggered schedules
• Aggregate replacement cost over 10 years is high
• Lower efficiency per gallon than central systems

Central boiler / high-efficiency commercial systems

One or two large commercial boilers (or a bank of them) serving hot water to every unit via a recirculating loop.

Pros:

• Fewer failure points, easier to maintain
• Higher efficiency (condensing boiler tech)
• Uniform pressure and temperature across units
• Building owner controls the equipment
• Better data on usage (submeter each unit)

Cons:

• Central failure = entire building loss
• Requires mechanical room and dedicated venting
• Recirculating loop needs periodic descaling and pump replacement
• Higher up-front cost
• If owner pays hot water in the lease, no per-unit incentive to conserve

Hybrid: central + tankless in-unit

Some newer Addison developments do a hybrid — central preheat with in-unit tankless boosters. Best of both, most complex to install.

The right answer for Addison-specific buildings

1970s–80s townhome-style multifamily (small footprint, few units): Stick with unit-by-unit. Replace tanks proactively on a 12-year cycle.

1990s–2000s garden-style apartments (larger, mechanical rooms exist): Central boiler makes sense on major overhaul. Otherwise unit-by-unit.

High-rise condos (dense, per-unit ownership): Central systems dominate. Individual condos may have supplemental tankless.

Mixed-use (retail below, residential above): Central boiler with recirculating loop — the retail side often demands high commercial output that unit-by-unit cannot provide.

The cost-of-ownership math

For a typical 100-unit Addison multifamily, over a 20-year horizon:

• Unit-by-unit tanks: 2x replacement cycles per unit + individual T&P / expansion tank / pan work — significant aggregate cost
• Central condensing boiler: One major install + preventive maintenance + one probable major overhaul

The central-boiler path usually wins on a 20-year TCO for buildings 50+ units. Below that, unit-by-unit wins on simplicity.

Hard water — same issue either way

Dallas hard water attacks both systems. Central boilers scale up faster than most owners plan for; unit-by-unit tanks scale at the same rate but with less catastrophic failure risk. Softening the incoming water at the building level solves it for both.

When to reevaluate

• Water heaters are failing on batch schedules across units
• Central boiler is at 15+ years and needs major service
• Building major renovation planned
• New submetering / billing rules make per-unit measurement worth it

Our commercial plumbing team has installed and serviced both configurations across Addison multifamily. We do free cost-of-ownership consultations for property managers evaluating the switch.