An indirect water heater is a storage tank with no burner of its own, kept hot by circulating water from the home's gas boiler through an internal coil.
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Quick answer
An indirect water heater is an insulated storage tank that holds domestic hot water and contains a heat exchanger coil, through which hot water from the home's gas space-heating boiler circulates to keep the stored water at temperature. It has no burner, gas connection, or flue of its own, relying entirely on the boiler as its heat source. This makes it a natural pairing for homes that already have, or are installing, a gas boiler for space heating, since one heat source then handles both jobs. It suits Metro Vancouver homes with radiant or hydronic heating where a boiler is already central to the mechanical system.
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Inside an indirect water heater, a coiled heat exchanger sits submerged in the stored domestic water. The home's boiler circulates its own heating water through that coil whenever the tank calls for heat, transferring warmth into the surrounding domestic water without the two water supplies ever mixing. Once the tank reaches its set temperature, a control shuts off circulation to the coil until the tank cools enough to call for heat again, similar in concept to how a thermostat cycles a furnace, just applied to stored water instead of room air.
Because the transfer happens through a sealed coil, the boiler's heating water, which may include additives depending on the system, stays completely separate from the domestic water that comes out of your tap.
Many Metro Vancouver homes with hydronic baseboard, radiator, or in-floor radiant heating already have a gas boiler as the central heat source for the house. Adding an indirect tank to that same boiler means the household gets domestic hot water without installing a second combustion appliance, a second vent, or a second gas connection. For homes without a boiler already, such as those with a furnace and separate water heater, installing a boiler purely to add an indirect tank is a bigger step and usually only makes sense alongside a broader heating system change.
| Feature | Indirect tank | Standalone gas water heater | Tankless |
|---|---|---|---|
| Own burner | No | Yes | Yes |
| Own vent | No | Yes | Yes |
| Stored hot water reserve | Yes | Yes | No, heats on demand |
| Depends on another appliance | Yes, the boiler | No | No |
An indirect tank needs to be sized to the household's hot water demand, and the boiler needs enough spare capacity to recover the tank's temperature promptly even while also serving space heating. Many systems use a priority control that temporarily favours the indirect tank over space heating for the few minutes it takes to reheat, since hot water demand is usually short and urgent while a brief pause in space heating during a reheat cycle is rarely noticeable. This priority logic and the boiler's overall sizing are things a licensed technician works out based on the specific home, not a generic formula.
If any of these do not fit your home, a standalone gas water heater or a tankless unit may be a better match, and a technician can walk through the trade-offs during an in-home assessment.
Safety note
If you ever smell gas near a boiler, water heater, or vent, do not investigate further: leave the home first, then call FortisBC at 1-800-663-9911. Combustion appliances should only be serviced by a Technical Safety BC licensed gas fitter.
No, it has no burner at all; it is heated entirely by circulating hot water from the home's gas boiler through an internal coil.
Most boilers can be paired with an indirect tank if they have enough spare heating capacity, which a technician needs to confirm before installation.
A regular gas water heater has its own burner and vent and operates independently, while an indirect tank has neither and relies entirely on the boiler.
Yes, an indirect tank cannot function without a boiler as its heat source, so if you do not already have one, this is not a standalone option.
Often yes, since homes with radiant heating already have a boiler as the central heat source, making an indirect tank a natural addition.
Sizing depends on household hot water demand and boiler capacity, and should be assessed by a licensed technician rather than estimated generically.
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