Manifolds vs. Low Loss Headers in Hydronic Heating

Hydronic heating design often comes down to a very practical question:
how should we manage water circulation and pumps? In most systems
the choice is between using a manifold for direct
distribution or installing a low loss header (LLH)
to provide hydraulic separation. Both approaches are valid, but their purpose and
effect on system stability are quite different.

A manifold can be imagined as a central hub where supply
water is divided into several branches. Each of these branches can be equipped with its
own pump or zone valve, making it very convenient when there are multiple heating zones,
such as with underfloor heating or a mix of small radiator circuits. The design is compact
and efficient, and the manifold ensures that each zone receives just the flow it requires
without significant interference from the others. For example, a simple 2-inch supply and
return manifold feeding several underfloor heating loops in a house is a straightforward
solution that provides excellent zoning and easy control.

A low loss header, on the other hand, serves a different
role. Instead of simply dividing flow, it separates the primary circuit of the heat source
from the secondary circuits of the building distribution. This is particularly important
when there are multiple pumps in the system, since without separation the pumps can compete
with each other and create unstable flows. The LLH ensures that the boiler or heat source
always sees a stable, predictable flow regardless of what the distribution side is demanding.
A common arrangement is a 2 × 4 inch LLH connected on the primary side to a
condensing gas boiler, while the secondary side feeds several variable-speed circuits such
as underfloor heating manifolds, radiator loops, a domestic hot water cylinder, or even a
solar buffer tank.

In practical terms, manifolds are ideal for small to medium
sized systems where zoning flexibility and compactness are more important than full hydraulic
independence. Low loss headers become essential as soon as
the system grows larger, combines different types of emitters, or integrates multiple energy
sources such as solar panels, heat pumps, or traditional condensing boilers. The LLH acts as
the stabiliser of the system, ensuring the boiler operates efficiently while the secondary
circuits take exactly the flow they need.

For many engineers the best solution is often a combination: a
low loss header on the boiler side to guarantee hydraulic
stability, followed by manifolds that split the flow into
zones such as underfloor heating, radiators, and hot water production. In this way the LLH
ensures smooth operation of the heat source, while the manifolds give flexibility and control
to the building’s various circuits.

In short, manifolds provide
distribution and zoning, while
low loss headers provide
separation and stability. Both are essential tools in modern
hydronic design, and together they create systems that are efficient,
expandable, and future-proof.