A hot water recirculation loop trades energy for convenience: an uninsulated loop run continuously loses roughly 10–15 W per metre of pipe, which on a 20-metre loop can exceed what the cylinder itself loses all day. Insulating the whole loop and controlling the pump — timer, return thermostat at about 55 °C, or demand activation — recovers most of that loss while keeping instant hot taps.
How much energy does a hot water recirculation loop waste?
An uninsulated secondary return running continuously loses roughly 10–15 W per metre of pipe at 55 °C — so a typical 20-metre loop dissipates 200–300 W around the clock, or 5–7 kWh per day. Compare that with the cylinder itself: declared standing loss across a real tank range such as Solimpeks' Solibuffer series runs 54–220 W depending on size and class, or about 1.3–5.3 kWh per day. In other words, an uncontrolled, uninsulated loop can waste more heat than the tank it serves. The fix is layered: continuous pipe insulation cuts the per-metre loss by roughly 70–80%, and pump control eliminates the hours when nobody needs instant hot water. Neither removes the comfort benefit — water arrives at distant taps in seconds instead of running cold down the drain.
What are the options for controlling a secondary return pump?
Control the pump by time, by temperature, or by demand — in rising order of savings. Continuous operation is the default on many older installations and the worst choice on every count:
| Control strategy | How it works | Energy verdict |
|---|---|---|
| Continuous | Pump runs 24/7 | Maximum loss; no benefit at 3 a.m. |
| Timer | Pump runs in scheduled comfort windows (morning/evening) | Cuts losses roughly in proportion to hours off |
| Return thermostat | Pump stops when return pipe reaches ~55 °C, restarts as it cools | Prevents pointless circulation of already-hot pipework |
| Demand-activated | Button, motion or flow sensor triggers a short circulation burst | Largest saving; loop is hot only when someone wants it |
The strongest practical setup combines them: a timer window, a return thermostat inside it, and full insulation throughout — guidance echoed by the US Department of Energy, which recommends timer and demand controls for circulation systems. Whether the cylinder itself should stay on all day is a separate question, answered in is it cheaper to leave the hot water on all day.
Does a recirculation loop damage tank stratification?
Yes — this is the loop's hidden cost. The secondary return delivers lukewarm water back into the cylinder, and if it enters too high or flows too fast it stirs the tank, eroding the hot-top/cold-bottom layering that makes stored heat usable. Degraded stratification means the top of the tank cools sooner, backup heating fires earlier, and any solar or heat pump input works against a warmer bottom zone. Good practice: connect the return low on the cylinder (or via a dedicated low return connection), size the bronze or stainless circulator small — a loop needs a trickle, not a torrent — and let temperature control stop the pump as soon as the loop is hot. The physics of why layering matters so much is covered in what is tank stratification and why does it matter, and the loop's contribution to daily losses belongs in the same budget as how much heat a hot water cylinder loses per day.
What about legionella in a circulating hot water system?
A circulating loop must stay hot enough to stay safe: UK HSE guidance for hot water systems under legionella control expects water to return from the loop at no less than 50 °C, with 55 °C recommended in healthcare settings. That sets a floor under your control strategy — a timer that leaves a long loop sitting lukewarm for most of the day creates exactly the 20–45 °C window in which legionella multiplies, especially in dead legs beyond the loop. Demand and thermostat controls are safer than crude long-off timers because the loop reheats fully whenever it runs, and periodic thermal disinfection of the whole circuit remains available through the cylinder's anti-legionella cycle — temperatures and durations are tabulated in what temperature kills legionella. In homes, the pragmatic balance is a timed-plus-thermostat loop at normal storage temperature; in commercial buildings, follow the written legionella scheme rather than optimising energy alone.
Should I install a recirculation loop at all?
Only when pipe runs make waiting genuinely wasteful — typically when distant taps take more than 10–15 seconds to run hot. Below that, the water and time saved rarely repay the standing loss, the pump electricity and the stratification penalty. Where the wait is long — large homes, hotels, multi-bathroom properties — a well-controlled, fully insulated loop is the right tool, and it pairs naturally with cylinders offering a dedicated return tapping. As a manufacturer, Solimpeks fits its larger cylinders with return connections for precisely this duty; the alternative for new builds is simply shorter, better-routed pipework.
Frequently asked questions
Does a hot water recirculation pump use a lot of electricity?
The pump itself is small — usually 5–25 W — so the electricity is minor. The real cost is heat: the loop turns the whole pipe run into a radiator, losing 10–15 W per uninsulated metre, which dwarfs the pump's own consumption.
What temperature should a secondary return come back at?
UK HSE guidance expects at least 50 °C at the return in systems managed for legionella, with 55 °C in healthcare premises. A return thermostat set around 55 °C both satisfies this and stops the pump once the loop is hot.
Can I just switch the recirculation pump off at night?
Yes — a timer that shuts the loop overnight and in empty daytime hours is the simplest worthwhile control, and reheating the loop takes only minutes. Keep storage temperature at its normal setpoint and run the loop hot whenever it operates.
Why does my tank cool faster since adding a recirculation loop?
The loop adds continuous pipe losses and returns lukewarm water into the cylinder, which disturbs stratification and cools the usable top zone. Insulate the loop completely, connect the return low on the tank, and fit thermostat or demand control on the pump.