How an indirect-fired water heater uses an existing gas boiler to produce domestic hot water, and when it's a good fit for a Richmond home.
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Quick answer
An indirect water heater is a storage tank heated by a home's existing gas boiler through an internal heat exchanger coil, rather than having its own burner. In Richmond, this is most relevant for newer homes built with hydronic in-floor heating or radiant systems already tied to a boiler, where adding an indirect tank can serve domestic hot water needs without installing a separate standalone gas water heater.
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An indirect water heater is an insulated storage tank with a heat exchanger coil inside it, connected to a boiler's hydronic loop. Hot water from the boiler circulates through the coil, heating the domestic water stored in the tank without the two water supplies ever mixing. The boiler's controls prioritize a call for domestic hot water similarly to how they manage a heating zone, and the tank holds enough hot water to bridge gaps between boiler cycles.
Because the boiler is already producing heat for the home's hydronic system, using it to also heat domestic water can be more efficient than running a separate burner in a standalone tank, particularly with a well-sized, modern boiler.
Richmond has seen substantial newer residential construction over the past couple of decades, and a good number of these homes were built with in-floor radiant heating tied to a gas boiler as the primary heat source. In these homes, adding an indirect tank is often a straightforward extension of an already-capable system, rather than requiring a new heat source to be installed. This is worth discussing at the point of any boiler service or replacement, since the marginal cost of adding domestic hot water capacity to an already-sized boiler is often less than installing an entirely separate gas water heater.
| Household situation | Indirect tank consideration | Notes |
|---|---|---|
| Smaller household, boiler with spare capacity | Standard-size indirect tank usually adequate | Boiler recovery speed matters more than raw tank size here |
| Larger household or high simultaneous demand | Larger indirect tank recommended | Provides more buffer between boiler heating cycles |
| Boiler already near capacity for heating zones alone | Evaluate during boiler sizing, possibly with replacement | Adding hot water demand to an already-stretched boiler can affect both functions |
| Home with forced-air heat only, no boiler | Not applicable | A standalone gas or tankless water heater is the appropriate choice |
Adding an indirect tank to an existing boiler system involves piping the tank into the hydronic loop, installing a dedicated zone valve or circulator for the domestic hot water call, and confirming the boiler's control system properly prioritizes that call. In Richmond's slab-on-grade homes, mechanical room space is often more limited than in a home with a full basement, so tank size and placement need to be planned around the available footprint, particularly if the mechanical room also houses other equipment.
An indirect tank isn't automatically the better choice in every situation. If a home's boiler is already running close to its capacity limit for heating zones, or if the mechanical room genuinely doesn't have space for an additional tank, a standalone gas or tankless water heater may be the more practical option. A technician should walk through both paths based on the specific boiler's capacity and the home's layout rather than defaulting to one approach.
Safety note
If you ever smell gas, hear a hissing sound near a gas line, or notice soot, a yellow or flickering burner flame, or a pilot light that will not stay lit, leave the house first and call from outside. Then call FortisBC at 1-800-663-9911 to report it. Do not try to relight a pilot or reset anything yourself until the line has been checked. Any work on gas piping, venting, or combustion appliances in BC must be done by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870 and boiler licence LBP0046450.
Often yes, since the boiler serving the radiant system is already a capable heat source, and adding an indirect tank can be a straightforward extension rather than requiring a new appliance.
Yes, particularly in slab-on-grade Richmond homes where mechanical room footprint can be more limited than in a home with a full basement, so tank size needs to fit the available space.
Adding an indirect tank increases total demand on the boiler, so a technician should confirm there's enough spare capacity, or discuss whether a standalone water heater is the better option instead.
Often yes, provided the existing boiler has enough capacity and appropriate controls. It depends on the specific system, which a technician can assess.
An indirect tank stores hot water heated by the boiler, while a tankless unit heats water on demand with its own burner. The better fit depends on whether a boiler is already in place and has capacity to spare.
No, since it doesn't have its own burner — it relies on the boiler's existing venting and combustion system, which simplifies installation compared to adding a second gas-fired appliance.
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