The vent route decides the equipment type
Venting is the first constraint because it usually decides what can go in. A standard-efficiency atmospheric storage tank vents by natural draft through a 3 in or 4 in draft hood into a chimney or B-vent, and FortisBC describes standard-efficiency storage tanks as typically needing a vertical chimney or B-vent through the roof. Where that flue is missing, damaged or being removed, an atmospheric tank is the wrong choice regardless of price.
High-efficiency water heaters require a dedicated vent and can be vented horizontally through an outside wall, FortisBC notes, and where the vent has to travel a distance it may need power venting with fans or blowers. A condensing tankless unit such as the Rinnai RU199iN or the Navien NPE-240A2 uses 2 in or 3 in PVC, CPVC, polypropylene or approved stainless pipe; the RU199iN allows 65 equivalent feet in 2 in and 150 feet in 3 in. A power-vent storage tank is the middle path where a horizontal route exists but a tank is wanted.
Combustion air and clearances
An atmospheric tank draws combustion air from the room it sits in, so a sealed or tightly built mechanical closet can starve it. The Bradford White RG240T6N is a natural-draft unit that needs a suitable chimney or B-vent and combustion air from the room; that is why it is the natural like-for-like replacement where a working flue exists, and a poor fit where the room is being sealed.
A forced-draft condensing tankless unit is different: it draws its combustion air through the same concentric or twin-pipe system, and Navien lists zero clearance to combustibles for the NPE-240A2. Clearances to walls, doors and stored goods are checked against the specific model's installation manual, not assumed from the unit being removed.
Gas supply capacity
A like-for-like atmospheric tank on natural gas draws around 40,000 BTU/h and connects to a 1/2 in gas line, as the RG240T6N does. A 199,000 BTU/h condensing tankless unit draws roughly five times that and connects to 3/4 in, as the RU199iN and the NPE-240A2 both do. The existing line, its length and the meter's capacity are checked before a tankless unit is proposed, because a supply that fed a tank may not carry a tankless unit.
FortisBC's process for a service upgrade is that if the added appliances significantly raise gas use and the gas fitter needs a meter exchange, because a different sized regulator or a larger meter is required, the gas fitter contacts FortisBC with the delivery pressure required and the total load in BTU, and FortisBC determines the process and timeline. That is a separate step from the appliance work and is planned into the schedule rather than discovered on the day.
Condensate, water and power
A condensing tankless unit produces acidic condensate that has to drain to an approved location, through a neutralizer where required, and it needs a 120 V receptacle for the controls and fan. The RU199iN's condensate connection is 1/2 in NPT and the unit runs on 120 V; the NPE-240A2 also runs on 120 V. An atmospheric tank needs none of that and keeps delivering hot water during a power outage, which matters in a region with winter storms.
Water connections are checked too. Both the tank and the tankless units use 3/4 in NPT for cold in and hot out, but a conversion usually adds isolation valves for future flushing, and the RU199iN ships with them. A unit mounted on a wall also has to be supported and spaced per the manual, which is a framing and location question, not just a plumbing one.
The permit and who may do the work
In BC a gas water heater replacement needs a gas permit. Technical Safety BC issues the permit outside seven local-government areas, while Vancouver, Richmond, Burnaby, Maple Ridge, the City and District of North Vancouver, and Kelowna issue their own for in-scope work. A plumbing permit is also needed in municipalities such as Burnaby because the water heater is a plumbing fixture.
Not every owner may pull a homeowner permit: strata lots, non-strata duplexes and homes operating a business are excluded, and Burnaby adds homes with a secondary suite. Gas fitting work is otherwise restricted to licensed contractors. This site publishes no do-it-yourself instructions for gas lines, venting, combustion or safety devices, because those are the parts that must be done and inspected by a licensed gas fitter.
What the assessment checks
CANRO Heating & Cooling provides free written estimates for replacements and installations across its verified Metro Vancouver coverage. The assessment walks the flue route, measures the gas line and load, checks combustion air and clearances, confirms whether a condensate path and a receptacle exist, and reviews the permit path for the municipality. Only then is a tank, a power-vent tank or a tankless model proposed.
The estimator on this site gives a CAD ballpark first and shows conversion allowances such as venting, gas supply and condensate separately, so the like-for-like cost and the conversion cost are both visible before a written quote follows the visit.