Low-Loss Headers Explained
A low-loss header hydraulically separates the boiler loop from the system loops, so pumps don’t fight each other. Here is the plain-English version.
On multi-zone and higher-output systems you will often see a “low-loss header” (or hydraulic separator). It sounds technical, but the idea is simple: it lets the boiler and the rest of the system each have the flow they need without fighting one another. Here is how it works and why it matters.
The problem it solves
When a boiler pump and several zone pumps share the same piping, they interfere — one pump’s flow disturbs another’s, causing uneven heat and noise. As zones open and close, flow through the boiler swings, which condensing boilers dislike.
How the header works
A low-loss header is a vessel that connects the boiler loop and the system loops while hydraulically separating them. The boiler circulates its own steady flow on one side; the system pumps draw what they need on the other. Neither disturbs the other, and the boiler sees stable flow.
Bonus benefits
- It often doubles as an air and dirt separator.
- It protects condensing boilers by keeping flow steady.
- It simplifies adding zones or a cascade later.
Key takeaways
- A low-loss header hydraulically separates the boiler loop from the system loops.
- It stops pumps fighting each other and keeps boiler flow steady.
- It often also separates air and dirt — a useful two-in-one.
Frequently asked questions
Does every boiler need a low-loss header?
No — many simple single-zone systems do not. They earn their place on multi-zone, multi-pump or higher-output systems, and in cascades, where keeping boiler flow steady and pumps from interfering really matters.
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