France's order of 23 June 1978, as amended by the order of 30 November 2005, settles the recirculation question without ever using the word. It requires the volume of the final feed pipework, between the point of distribution and the draw-off point, to be as low as possible and in every case 3 litres or less, and the water to be at 50°C or above at every point of the distribution system. Past that 3-litre volume, keeping the water hot stops being a comfort choice and becomes an enforceable requirement, which a recirculation loop is the usual way to meet. The same text caps draw-off at 50°C in rooms intended for washing and 60°C in other rooms, which forces a mixing device downstream.
Understanding the DHW loop and its real impact on comfort
DHW: wait time at draw-off, temperature stability and daily use
Without recirculation, domestic hot water (DHW) takes as long as it takes to purge the lukewarm water left in the pipes. The result is a few tens of seconds of waiting, wasted water, and sometimes a temperature that "hunts" for its setpoint. With a well-designed system, the goal is stable comfort at the tap, especially at peak times.
The loop: continuous circulation principle and key network points
A DHW loop circulates hot water continuously through a flow-and-return loop, driven by a pump. The points that make the difference are simple: pipe insulation, balancing of the returns, limiting flow velocities, pump setting, and maintaining a sufficient temperature for hygiene. Otherwise comfort improves but losses climb. To frame sizing against actual needs, you can lean on DHW consumption benchmarks.
When a loop is essential: hotels, multi-unit buildings, large homes
It becomes almost unavoidable once network lengths get out of hand: hotels, apartment blocks with risers, or large homes with several bathrooms far from the tank. It cuts the wait and avoids complaints. In a small home, good layout or a local booster is often enough on its own.
Mapping the DHW distribution to decide where to loop
Lengths, diameters and draw-off points: what weighs on distribution
Measure on the drawing the metres of pipe between the tank and each draw-off point, then convert to litres: it is the volume, not the length, that the text regulates. The longer the run and the larger the diameter, the more the DHW cools, and the longer the wait at the tap. The same 3-litre rule drives the manifold distribution layout, which often keeps you under the threshold without any loop at all. Finally, spot the little-used sections: these are often "dead" volumes to deal with.
Full loop or partial loop: choosing based on the layout
A full loop delivers hot water almost instantly but increases heat losses and runs the pump more often. A partial loop targets only the distant or heavily used branches. The rule of thumb is simple: loop where the wait time is a problem, and leave the short, nearby runs on direct feed.
Positioning the tank, manifolds and returns: limiting unnecessary lengths
Place the tank and manifolds as close as possible to the "centre" of the draw-off points. Group the outlets, avoid detours, and route the loop return back by the shortest path. Every extra metre means more insulation, more losses and more balancing to manage. Keep continuous pipe insulation and accessible settings.
Reducing heat losses on a looped DHW system
Losses along the run: pipe insulation and singular points
On a DHW loop, losses mainly come from the metres of pipe. Aim for continuous insulation on the flow, return and tap-offs. Also treat the singular points: valves, flanges, pumps, supports, all plumbing items Argile prices into the quote from a works library and free-text lines. Interrupted insulation is a heat leak, like a window left ajar all year round.
Setpoint temperature and anti-Legionella: finding the right balance in 2026
The higher the setpoint, the more the network radiates heat, but the floor is not negotiable: 50°C at every point of the distribution system, loop return included. The cap is held downstream instead, with a mixing valve that brings draw-off below 50°C in a washing room. Here is what the text requires, and what serves as the commissioning checklist.
| Check point | Enforceable value | Where it applies |
|---|---|---|
| Volume of the final feed pipework | ≤ 3 litres, and as low as possible | between the point of distribution and the draw-off point |
| Water temperature | ≥ 50°C | at every point of the distribution system |
| Temperature at the draw-off point | ≤ 50°C | rooms intended for washing |
| Temperature at the draw-off point | ≤ 60°C | other rooms |
| Water in storage vessels of 400 litres or more | ≥ 55°C at the outlet at all times, or a daily temperature rise | preheating tanks excluded |
If needed, schedule an occasional temperature boost rather than permanent overheating. To frame the sanitary requirements, lean on anti-Legionella sanitary safety devices.
Mixing valves, check valves and balancing: avoiding parasitic hot returns
Poor balancing creates "phantom" loops and unnecessary hot returns. Fit check valves in the right places, check for mixing valves that let heat leak from the hot side to the cold, and set flow rates branch by branch. Clean balancing stabilises temperature, reduces pump start-ups, and cuts losses.
Control, pump and schedules: limiting losses without losing comfort
Pump control: schedules, feedback control and demand-triggered start
On a DHW loop, a pump running continuously heats the pipework for nothing. Schedule time windows around actual use (morning, evening) and cut it off overnight. Add feedback control based on a return-temperature sensor, or a restart on temperature drop, so it only starts when things cool down. In a house or small multi-unit building, a push-button can trigger it on demand with a short timer. Fewer losses, same comfort.
Choosing a suitable loop pump: flow rate, head, noise
Aim for a high-efficiency pump, ideally variable speed. Size the flow rate to actual need, then check the head against the length, pressure losses and fittings. A low-noise model makes a real difference in a service duct. Versions with a timer or dry-contact input make control simpler.
Balancing the returns: settings, valves, flow checks
Without balancing, the nearby returns take everything and the distant points stay lukewarm. Fit balancing valves, then adjust branch by branch. Check the actual flow rates with a flow meter, or via flow/return temperatures. Clean balancing stabilises control and reduces unnecessary cycling. To go further, see the principles of network balancing.
Site method: sizing, commissioning and checking performance
A quick loss calculation and estimate of possible savings
On a DHW loop, start from the concrete numbers: network length, diameter, insulation, flow temperature and ambient temperature. You get a sense of the linear losses and the kWh "leaking into the walls". Then compare two configurations: looping 24/7 versus a controlled loop (clock, thermostat, feedback control). Add the expected gain from properly insulating the accessible sections.
Commissioning: venting, temperature checks, measurements at distant points
Fill the system, vent the air at high points, then check the direction of circulation and that the check valves work correctly. Stabilise the setpoint, then check flow, return and mixed water temperatures. Measure at the distant points. Time the wait and record the temperature after a few tens of seconds. Adjust balancing so no single branch "steals" the flow. To go further on eliminating air pockets, see also avoiding air pockets in the network.
Common troubleshooting: lukewarm loop, long waits, overconsumption
A lukewarm loop often comes from too low a flow rate, missing balancing or missing insulation. Long waits point more towards a stuck check valve, an undersized pump or an open bypass. Overconsumption, meanwhile, usually comes down to too high a setpoint, a permanently running loop and losses in unheated spaces.
