Water heaters · System type

Gas storage tank water heaters

The conventional water heater: an insulated tank of 30 to 80 US gallons heated by a natural gas or propane burner underneath, vented by natural draft, power vent or direct vent. Sized by first-hour delivery, rated by UEF.

Natural gasPropane

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In short

A gas storage tank keeps a volume of hot water ready and reheats it with a burner. Its real capacity is the first-hour rating, not the nominal gallons. Atmospheric models need a chimney or B-vent and no electricity; power-vent and direct-vent models use a blower and side-wall venting and need a 120 V supply. They are the lowest-cost like-for-like replacement in most Metro Vancouver homes.

How a gas tank works

Cold water enters through a dip tube to the bottom of the tank, the burner heats the tank bottom, and hot water leaves from the top. A thermostat on the gas control holds the set temperature; a high-limit shuts the gas off if the water overheats. The tank is glass-lined steel protected by a sacrificial anode rod, and a temperature-and-pressure relief valve discharges if pressure or temperature exceed its rating.

Atmospheric-vent tanks draw combustion air from the room and vent by natural draft through a draft hood into a chimney or B-vent; they work without electricity. Power-vent tanks push exhaust through PVC or ABS pipe with a blower and can side-wall vent. Direct-vent tanks bring combustion air from outside through a sealed vent. Condensing gas tanks add a larger heat exchanger and a condensate drain for higher UEF.

Capacity: nominal volume, rated volume and first-hour rating

Three different numbers describe a tank. Nominal volume (40 US gal) is the marketing size. Rated or DOE storage volume (often 2 gallons less) is the tested volume. First-hour rating is how much hot water the tank can deliver in a busy hour from hot: stored volume plus recovery. The Bradford White RG240T6N, for example, is a 40-gallon nominal tank with a 75-gallon first-hour rating. Sizing uses the first-hour rating against your peak hour; the recovery rate tells you how quickly the tank comes back.

Efficiency and regulation

Gas storage tanks are rated by Uniform Energy Factor at a draw pattern set by the tank's first-hour rating. Canada's energy-efficiency regulations set a minimum UEF for gas storage water heaters manufactured on or after 1 January 2025 by a formula tied to first-hour rating and volume; ENERGY STAR version 5.0 requires UEF 0.81 or better for medium-draw tanks up to 55 gallons, which atmospheric models do not reach. A UEF is only comparable with another UEF at the same draw pattern, and never with a legacy EF.

Installation and safety points

Every replacement needs a gas permit and, in municipalities such as Burnaby, a plumbing permit. The relief-valve discharge must run to an approved location and must never be capped. BC's plumbing code limits shower and bathtub water to 49 °C, so a tank kept at 60 °C to limit Legionella needs a thermostatic mixing valve. Expansion control may be required on closed systems with backflow prevention or pressure-reducing valves.

Strengths

Lowest installed cost for like-for-like replacement
High simultaneous delivery from stored volume
Atmospheric models work during power outages
Simple controls; widely serviced

Limitations

Standby heat loss; atmospheric models have UEF around 0.6
Runs out during long peaks and must recover
Takes floor space; tank life typically 8–12 years
Atmospheric venting needs a sound chimney and room combustion air

Components that apply

Catalogue

Gas tank models documented

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Bradford White · Gas storage tank

Bradford White RG240T6N

CurrentSold in Canada

Nominal capacity: 40 US gal (33 Imp. gal, 151 L)
First-hour delivery: 75 US gal (284 L)
Input: 40,000 BTU/h

The Bradford White RG240T6N is a 40 US gallon (151 L) atmospheric-vent natural gas storage water heater with a 40,000 BTU/h input, 75 US gallon first-hour rating and UEF 0.64, sold in Canada through wholesale channels. It is the like-for-like replacement for most 40-gallon gas tanks in older Metro Vancouver homes.

Natural gasPropaneAtmospheric (draft hood)