Duplexes generally call for one tankless water heater per unit rather than a single shared system, especially where the two sides are independently owned.
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Quick answer
A tankless water heater works well in a duplex unit, and in most cases each side of the duplex gets its own independent unit rather than sharing one system, particularly when the duplex is separately titled with two separate owners.
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The same logic that applies to heating in a duplex applies to hot water: two owners or two independent households generally want their own equipment, their own maintenance schedule, and their own gas costs, rather than being tied to a shared system where one household's usage or a repair need affects the other.
In a side-by-side duplex, each unit typically has its own utility area — often near the laundry — where a tankless water heater can be wall-mounted with its own dedicated vent through that unit's exterior wall. In an up-and-down duplex, the two units' utility spaces may be stacked or offset, which needs more careful vent planning to avoid one unit's exhaust affecting the other unit's windows or air intakes.
A two-bedroom side of a duplex occupied by a couple has very different peak hot water demand than a three-bedroom side occupied by a family of five, even in the same building. Each unit's tankless water heater should be sized to that unit's fixture count and expected simultaneous use, not to a blanket assumption based on the building as a whole.
Independently owned or metered duplex units are generally treated as separate mechanical scopes by Metro Vancouver municipalities, meaning two permits rather than one, and FortisBC needs to confirm each unit's meter can support its own tankless appliance if that isn't already established.
| If the unit has | Best hot water approach |
|---|---|
| A forced-air furnace already handling heat | Standalone tankless water heater |
| Hydronic heat (radiators or in-floor) | Combi boiler may cover both heat and hot water in one unit |
A tankless water heater installation in one duplex unit generally runs $3,500–$7,500 as a ballpark, not a quote, and a duplex opting for independent systems on both sides should budget for that as two separate installations.
With two independent tankless water heaters in a duplex, each owner is responsible for their own annual maintenance, such as descaling and a general inspection of the venting and gas connections. This is worth spelling out clearly at the time of installation, especially in a rental duplex where a landlord and tenant relationship, rather than two owners, is involved, so there's no confusion later about who arranges service. Keeping the two systems' maintenance records separate also makes it easier to track each unit's specific service history if a warranty question ever comes up.
It's also worth each owner or tenant knowing where their unit's shutoff valve is located, since a leak or an emergency situation calls for being able to isolate that specific system quickly without needing to track down the other household first.
Not every gas fitter has experience coordinating two independent gas appliances in one building at the same time, so it's worth asking a prospective contractor about their experience with duplexes specifically before booking the work. A tech who regularly handles multi-unit properties will already know to check both meters, both vent paths, and both units' clearances as part of a single coordinated visit, which tends to go more smoothly than treating the two installations as entirely separate appointments.
Safety note
Any gas line, venting, or combustion-related work on a boiler or tankless water heater must be done by a Technical Safety BC licensed gas fitter. CANRO holds gas licence LGA0043870 and boiler licence LBP0046450. If you ever smell gas or suspect a venting or carbon monoxide problem, leave the home immediately and call FortisBC at 1-800-663-9911 before doing anything else.
In most cases yes, especially in separately titled duplexes with independent ownership, since it keeps each unit's hot water, maintenance, and gas costs independent of the other side.
It shouldn't, as long as the vent is placed away from the neighbouring unit's windows, doors, and air intakes, which a licensed tech will plan for during installation.
Based on that specific unit's fixture count and expected simultaneous hot water use, independent of what's happening on the other side of the building.
Not necessarily if a meter already serves your unit independently and has adequate capacity, but this should be confirmed by a licensed gas fitter before installation.
There can be some efficiency in scheduling both jobs together, but each unit's installation is still its own scope of work, so overall cost reflects two separate installations.
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