Capacity means two different things
A storage tank keeps a volume of hot water ready and reheats it with a burner or element. Its useful capacity is the first-hour rating: the stored volume plus what it can reheat in a busy hour. A 40 US gallon (151 L) Bradford White RG240T6N is rated at 75 US gallons (284 L) first-hour, nearly double its nominal volume, because its 40,000 BTU/h burner recovers about 43 gallons an hour at a 50 °C rise.
A tankless unit stores nothing. Its capacity is a flow rate, in litres per minute or US gallons per minute, at a given temperature rise. The Rinnai RU199iN is rated 0.26 to 9.8 GPM and can be adjusted to 11 GPM (42 L/min), but Rinnai's curves apply only to inlet water at 21 °C or below and no rise is stated for the maximum. The harder the unit has to work, the less it can deliver.
Why the winter temperature rise decides tankless sizing
Metro Vancouver's water comes from mountain reservoirs, and in winter the incoming supply can be below 8 °C. To deliver 49 °C at a shower, the unit must raise the water by roughly 40 °C (72 °F). A shower-class fixture draws about 7.5 to 9.5 L/min (2 to 2.5 GPM), so two showers at once need about 17 L/min (4.5 GPM) at that rise. That is the figure to compare against the manufacturer's flow-at-rise table, not the brochure maximum.
Three simultaneous fixtures in January can exceed one 199,000 BTU/h unit. The honest options are a second unit, a storage buffer, or accepting that the third fixture waits. Tankless units also need a minimum flow to fire, 0.4 GPM (1.5 L/min) on the RU199iN, so a trickle from a low-flow tap may not start it.
| Fixtures at once | Approximate flow needed | Typical outcome with one 199,000 BTU/h condensing unit |
|---|---|---|
| One shower | about 9 L/min (2.5 GPM) | Comfortable |
| Two showers | about 17 L/min (4.5 GPM) | Check the flow-at-rise table; often marginal in January |
| Three or more | 25 L/min (6.5 GPM) or more | Usually exceeds one unit; assess two units or a buffer tank |
Reading the efficiency number
Both types are now rated by Uniform Energy Factor (UEF), which replaced the older Energy Factor (EF). UEF is measured under one of four draw patterns, and a value is only comparable with another value at the same pattern. The RG240T6N's UEF 0.64 is a medium-draw storage rating; the RU199iN's 0.95 is a high-draw tankless rating. The direction is real, since the tank loses heat through its jacket all day and the tankless unit does not, but the numbers are not a savings calculator, and WaterHeating.ca does not publish savings claims.
Canada's energy-efficiency regulations set a minimum UEF for gas storage water heaters by a formula tied to first-hour rating and tank volume, and ENERGY STAR version 5.0 requires UEF 0.81 or better for a medium-draw gas tank of this size. Neither the RG240T6N nor most atmospheric tanks meet ENERGY STAR; power-vent condensing tanks and condensing tankless units do.
Installation constraints are usually the deciding factor
A like-for-like atmospheric tank reuses the draft hood, chimney or B-vent, the existing 1/2" gas connection and needs no electricity. A condensing tankless unit needs 2" PVC, CPVC or polypropylene venting to an exterior termination (65 equivalent feet in 2" on the RU199iN), a 3/4" gas connection on a supply that can carry 199,000 BTU/h, a condensate drain for acidic condensate, a 120 V receptacle, and isolation valves for flushing.
In BC every gas water heater replacement needs a gas permit, and municipalities such as Burnaby add a plumbing permit because the water heater is a fixture. Strata and duplex owners must use a licensed contractor. BC's plumbing code limits shower and bathtub water to 49 °C, so a storage tank kept at 60 °C to limit Legionella needs a thermostatic mixing valve; tankless units default to a 49 °C set point.
- Choose a tank when a working flue exists, several fixtures run at once, or outages matter
- Choose tankless when wall space, a sealed vent route, gas capacity and a drain are available and demand is sequential
- Either way, size from measured demand, not floor area or bedroom count
Maintenance and lifecycle
Storage tanks need their sacrificial anode inspected (every two years on the Bradford White) and their relief valve exercised annually; the tank itself typically carries a 6- to 10-year warranty without labour. Tankless units need annual descaling as a warranty condition even in Metro Vancouver's soft water, and carry longer heat-exchanger terms, 15 years on the RU199iN with 5 years on parts and labour when registered.
Recirculation is the other lifecycle question. A tankless unit is not instant at a distant tap; hot water still travels through the pipes. A recirculation loop with an external pump and a dedicated return line or crossover valve shortens the wait but adds gas use and cost. The estimator itemizes it as an adder rather than assuming it.
What CANRO does at an assessment
CANRO Heating & Cooling provides free written estimates for replacements and installations in Metro Vancouver. The assessment counts fixtures and peak-hour use, checks the flue, gas supply, drain and electrical, and confirms the winter rise before proposing a tank size or a tankless model. The instant estimator on this site gives a CAD ballpark first, with the conversion allowance shown separately; the written quote follows the visit.