Why a tankless unit draws more gas
A storage tank heats a fixed volume with a modest burner and stores it. The Bradford White RG240T6N, a typical 40 US gallon atmospheric tank, uses a 40,000 BTU/h burner. A condensing tankless unit has no stored volume, so it must heat water as it flows, and its input is far higher: the Rinnai RU199iN is rated 15,000 to 199,000 BTU/h and the Navien NPE-240A2 is rated 13,300 to 199,900 BTU/h.
That is roughly five times the gas draw of the tank it replaces, and it is instantaneous rather than spread over a recovery period. The gas supply has to deliver that peak load without dropping below the unit's required pressure, which is why the line and meter are checked rather than assumed.
Line size and connection
The connection size differs as well. The RG240T6N connects to a 1/2 in gas line; the RU199iN and the NPE-240A2 both connect to 3/4 in. A larger connection is not by itself enough: the pipe run from the meter to the unit has to be sized for the load and its length, because pressure drops along the run. A short 3/4 in run and a long one are not the same supply.
The practical question at assessment is whether the existing line can carry the peak input at the required pressure. Where it cannot, the line is replaced or upsized as part of the installation, and that allowance is shown separately in the estimate.
Supply pressure
Both the RU199iN and the NPE-240A2 specify a natural gas supply pressure of 3.5 to 10.5 in. w.c. at the unit. A supply that sits at the low end under other loads, or that drops when the furnace and range are also running, can push a tankless unit outside its range and cause ignition or flame faults rather than an obvious outage.
That is why the check is done under load, not just at a static reading. The unit's own manual states the range, and the technician confirms the supply holds inside it while other gas appliances cycle.
When the meter or regulator changes
Sometimes the line is adequate but the meter is not. FortisBC's published process is that if you are adding natural gas appliances that will significantly increase your gas use, and your gas fitter needs FortisBC to exchange your meter because a different sized regulator or a larger gas meter is needed, the gas fitter contacts FortisBC with the delivery pressure required and the total load in BTU. FortisBC then determines the process and timeline.
That means the meter exchange is arranged by the gas fitter through the utility, using figures the fitter calculates, and it has its own lead time. It is planned into the project schedule rather than treated as a same-day step.
How the assessment verifies capacity
CANRO Heating & Cooling assesses gas supply as part of a tankless installation or conversion, and publishes supply-capacity assessment among its services. The assessment records the meter and regulator, the line size and run, the appliance load, and the required delivery pressure, then confirms the supply holds within the unit's range under load.
Written estimates for installations are free, and the gas supply work is itemized so it is visible before the job is approved. Whether a specific home needs a line change, a meter exchange, or neither is a site finding, not something that can be read off a model number.