Buffer Tanks Explained
A buffer tank adds thermal mass to a heating system, stopping short cycling on low loads. When you need one and how it differs from a storage tank.
On some systems — especially those with low-load zones or a powerful boiler serving small demands — a boiler short cycles, switching on and off too quickly. A buffer tank is a common, elegant cure. It is often confused with a hot-water storage tank, but it does a different job. Here is the distinction.
What a buffer tank does
A buffer tank is a vessel of system (heating) water that adds thermal mass to the loop. The boiler heats the buffer, and the system draws from it. That cushion stops the boiler firing for every tiny demand, smoothing operation and eliminating short cycling.
Buffer tank vs storage tank
- A buffer tank holds heating-loop water and stabilises the system.
- An indirect storage tank holds domestic hot water for taps and showers.
- They solve different problems and are sometimes both present.
When you need one
Buffer tanks earn their place where there are small or single low-load zones, where a boiler is large relative to the smallest demand, or in some heat-pump-and-boiler hybrid systems. If your boiler short cycles on light loads despite good modulation, a buffer is a likely remedy.
Key takeaways
- A buffer tank adds thermal mass to the heating loop to stop short cycling.
- It is different from a domestic-hot-water storage tank.
- It helps where loads are small relative to boiler output.
Frequently asked questions
Do I need a buffer tank?
Only if your system short cycles on low loads or has small zones that a powerful boiler over-serves. Many correctly-sized, well-modulating systems do not need one. A technician can tell from how the boiler cycles.
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