Indirect Water Heaters Explained
An indirect tank uses your boiler to make domestic hot water — efficient, high-volume and long-lasting. Here is how it compares to a combi or standalone tank.
If you have a system boiler rather than a combi, your domestic hot water probably comes from an indirect water heater. It is one of the most efficient and durable ways to make hot water in a home that already has a boiler — here is how it works and when it is the right choice.
How it works
An indirect tank is a well-insulated storage cylinder with a heat-exchange coil inside. Your boiler heats water and pumps it through that coil, transferring heat to the domestic water in the tank. The boiler — not a separate burner — does the heating, so there is no second combustion appliance to maintain.
Why it is efficient
Because it borrows the boiler’s efficient burner and the tank is heavily insulated, standby losses are low and recovery is fast. The boiler typically prioritises hot water briefly when the tank calls, then returns to heating.
Indirect vs combi vs standalone
- Indirect: large stored volume, great for multiple bathrooms; needs space for the tank.
- Combi: instant hot water with no tank, but flow rate is limited by the boiler.
- Standalone gas tank: independent of the boiler, but a second appliance to service.
Key takeaways
- An indirect tank uses your boiler’s burner to heat stored domestic hot water.
- It offers high volume and fast recovery with low standby losses.
- Choosing indirect vs combi comes down to simultaneous demand and available space.
Frequently asked questions
Is an indirect water heater better than a combi?
For homes with several bathrooms or high simultaneous demand, an indirect tank usually delivers better, steadier hot water. A combi is excellent for smaller homes and saves the tank space. The right choice depends on your usage and layout.
How long do indirect tanks last?
Often longer than a standard gas water heater — frequently 15+ years — because there is no burner or flue inside the tank to corrode. Water quality and the anode rod still affect lifespan.
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