A new build is the easiest place to size a tankless system correctly, because gas line, vent path, and fixture layout can all be planned before drywall goes up.
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Quick answer
A new build gives a tankless water heater the best possible installation conditions, because the gas line diameter, vent path, mounting location, and fixture count can all be planned together at the framing and rough-in stage instead of retrofitted around existing walls, but the unit and its venting still need to be sized against the home's finished fixture count, not a placeholder builder estimate.
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On a retrofit, a technician has to work around whatever gas line and chimney already exist. On a new build, all of that is still open for decisions, which means the gas line can be sized correctly the first time instead of upsized later, and the vent termination can be placed where it has full code clearance from windows, doors, and property lines rather than wherever happens to be available.
The mistake CANRO sees most often on new construction is a water heater location chosen purely for interior layout convenience before anyone confirms it has a clean, code-compliant path to an exterior wall or roof for venting.
Builders sometimes plan mechanical rough-ins from an early floor plan before bathroom counts, ensuite layouts, or a future basement suite are finalized. Sizing the tankless unit and its gas supply against the actual finished fixture count, including any secondary suite or laneway home sharing the same gas meter, avoids a system that is technically installed correctly but undersized for how the finished home will actually be used.
A sealed-combustion tankless vent needs specific clearances from windows, doors, intakes, and property lines, and on a new build with tighter lot setbacks, particularly common on Vancouver and Burnaby infill lots, that clearance can be harder to find than it looks on paper. Deciding the vent path at framing avoids discovering a conflict after siding and windows are installed.
Because the water heater's gas demand adds to the home's total gas load alongside a furnace or boiler and any gas range or fireplace, the mechanical contractor sizing the gas meter and main line needs the water heater specification in hand early, not as an afterthought once framing is done.
| New Build Decision | Why It Matters |
|---|---|
| Gas line diameter | Must reflect total household gas load, not just the water heater |
| Vent termination location | Needs clearance from windows, doors, intakes, property lines |
| Mechanical room location | Shorter runs to main fixtures reduce wait time |
| Future suite or laneway home | Changes whether one unit or two units make sense |
Once a tankless system is installed in a new build, keeping the manufacturer's installation manual, the permit and inspection records, and the technician's commissioning notes on file is worth the small effort. This documentation supports any future warranty claim, helps a future service technician understand the specific configuration installed, and is useful if the home is sold and a buyer's inspector has questions about the mechanical system.
Safety note
Any work on the gas supply line, venting, combustion air, or the burner assembly of this equipment 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, hear a hissing sound near the unit, or suspect a carbon monoxide problem, leave the home immediately and call FortisBC at 1-800-663-9911 from outside before doing anything else.
Before, ideally at the rough-in planning stage, so the gas line and vent path can be confirmed against the actual framing rather than adjusted afterward.
It depends on total household gas load across all appliances; your mechanical contractor calculates this from the full equipment list, not the water heater alone.
Many Bosch tankless models support either roof or sidewall venting; the right choice depends on the home's layout and which path gives cleaner clearances.
Often yes, since running the piping during construction is far less disruptive than retrofitting it later if wait times at a distant ensuite turn out to be longer than expected.
Gas appliance installation requires permitting through your municipality and must be done by a licensed gas fitter; your contractor typically handles this as part of the mechanical permit.
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