Hydraulic schematic: 10 standard configurations

Reading a hydraulic schematic without getting it wrong

The symbols and connections to know (flow, return, tapping, bypass)

On a hydraulic schematic, start by identifying the flow and the return. Arrows give the direction. A tapping represents a branch to an emitter or a loop. A bypass is an alternative path, useful for maintaining a minimum flow rate or isolating a component without shutting down the whole system.

The essential components: circulators, valves, check valves, air vent, relief valve

The circulator is the driver of the flow rate. Check its position relative to the generator and the manifolds. Valves are used to isolate, adjust and balance. The check valve prevents backflow when a circuit stops. The air vent purges air. The relief valve protects against overpressure. Identify these components before touching any setting.

Points to watch on site: diameters, pressure losses, direction of flow

A schematic doesn't tell you everything. On site, confirm the diameters actually installed, the consistency of the pressure losses and the available head. Follow the actual direction of flow. A valve or check valve fitted backwards is enough to cause noise, flow faults, or a heat pump going into fault.

Standard hydraulic configurations for heating only

Direct radiator circuit: simple schematic and use case

In a retrofit, the simplest setup remains a single flow and return on one radiator circuit. On the hydraulic side, aim for short and legible. A circulator, an isolation valve, a filter and a dirt separator are often enough. This setup suits emitters that are already sized correctly, especially if the heat pump can hold a moderate flow temperature.

Underfloor heating circuit: mixing, 3-way valve and low-temperature protection

Underfloor heating needs lower, more stable water temperatures. Add a mixing group with a 3-way valve and a secondary circulator. The sensor and the weather compensation curve drive the mixing to avoid sudden swings. Low-temperature protection is handled through a limiter, setpoint adjustment and overheat safety, to keep floor comfort without risk.

Two circuits at different temperatures: balancing and operating priorities

Radiators upstairs, underfloor heating on the ground floor. Decoupling (low-loss header or manifold) secures the flow rates. Plan for:

• Flow rate adjustment and balancing valves.
• Priority to the most demanding circuit, according to the control strategy.
• Motorised valves to prevent overly hot return water.

Standard hydraulic configurations with a tank and domestic hot water

Buffer tank: when the hydraulic schematic secures system stability

The buffer tank adds thermal inertia to the hydraulic circuit. It smooths a heat pump's starts, limits short cycling and makes it easier to decouple flow rates between the primary loop and your secondary networks (radiators, underfloor heating, zones). In a retrofit, it's also a clean "buffer" point for connecting a backup heater or a second source, without destabilising the control strategy.

DHW production with a tank: heat exchanger, DHW priority and anti-legionella in 2026

With a DHW tank, you choose production via a heat exchanger (coil or plates) or direct storage, depending on the generator. DHW priority via a 3-way valve avoids drawing on heating while the tank is recharging. In 2026, plan for a controlled anti-legionella cycle (a periodic rise to high temperature) and an outlet mixing valve to keep the tap temperature safe.

DHW recirculation loop: cutting wait time while controlling flow rates

A DHW recirculation loop reduces the wait at draw-off points, but it can increase losses. To keep the hydraulics lean, insulate the network, limit the loop to the sections that need it, fit balancing components and control the pump (clock, thermostat, interlock). The goal is a controlled flow rate and hot water on tap, without needlessly heating the pipe runs.

Standard hydraulic configurations with a heat pump and mixed generators

Direct air-to-water heat pump: feasibility conditions and key settings

Connected directly to radiators or underfloor heating, feasibility mainly depends on the flow temperature. Aim for emitters capable of heating with 35 to 55°C. Check the flow rate, hydraulic balancing and a sufficient water volume to avoid short cycling. Key settings: weather compensation curve, a consistent ΔT, circulators at the right speed, and a magnetic filter to protect the heat exchanger.

Heat pump + boiler in backup: hydraulic logic, control and safeties

In a backup setup, the heat pump covers the base load, the boiler takes over at the bivalent point, usually defined by outdoor temperature and available output. On the hydraulic side, plan for check valves, a 3-way valve or decoupling via a buffer tank depending on the flow rates. The control logic must interlock the generators to prevent double heating, and keep heat pump priority whenever possible.

Heat pump + wood boiler stove: decoupling, protections and field feedback

With a wood boiler stove, the circuits are almost always separated via a buffer tank to absorb peaks. Add a thermal relief valve, a cooling loop and overheat safety, essential with wood. In the field, a dirt separator, air venting and a stable hot return make the difference in limiting corrosion and fouling.

Standard hydraulic configurations for retrofits: decoupling and network balance

Low-loss header: when the hydraulics avoid flow rate conflicts

In a retrofit, flow rates don't always match neatly between the generator and the emitters. A low-loss header acts as a buffer zone. It lets each circulator work at its own pace, while stabilising the flow temperature. It's often the right option with multiple circuits, or when the existing network is "pulling" too hard.

Manifolds and existing networks: identification, venting and refilling without surprises

Before starting the system back up, clearly identify the flows, returns and adjustment components. A methodical venting process avoids air pockets that throw off the hydraulic balance and wear out the pump.

• Identify the isolation and drain valves.
• Vent from the highest point toward the boiler or heat pump.
• Check cold pressure and tightness.

Commissioning checks: temperatures, ΔT, flow rates and fine-tuning the circulators

At commissioning, measure flow, return and the target ΔT according to the manual and the type of emitters. Check the flow rates at the manifolds, then adjust the circulators (speed or constant pressure). A fine-tuned system shows quickly: less noise, even temperatures across rooms, longer cycles.