The water temperature that unlocks real boiler savings

Lowering boiler water from 70 to 60 degrees saves gas

What temperature should you set the radiator water to so you don't overpay on your gas bill? The short answer: as low as possible while still heating the house. The long answer depends on the boiler, the type of circuit and how cold it is outside. On a conventional, non-condensing boiler there is room for improvement, but it is modest, and anyone expecting miracles will be disappointed.

The starting point is a very common question: a sealed standard boiler, non-condensing, that allows the radiator water temperature to be set between **45 and 80 degrees**, with aluminium radiators. Many installers are tempted to leave it at **70-80 degrees** so the radiator spreads the heat. The logic of saving energy says exactly the opposite.

Why lowering the water temperature reduces consumption

The lower the boiler's output temperature, the smaller the losses and the higher the efficiency. The problem is that lower water temperature means less heat delivered by the radiator. The balance lies in turning it down as much as possible while the home still reaches the set temperature. **80 is better than 90, 70 better than 80, 60 better than 70**, as long as you don't feel cold.

This is where the type of installation comes in. In a single-pipe circuit, all the water passes through every radiator, and the last one receives water several degrees cooler than the first; lowering the flow temperature too much leaves the last radiators lukewarm. In a two-pipe circuit, the water passes through one radiator at a time and they all reach roughly the same temperature. The conclusion is uncomfortable for those who advocate savings at any cost: on a single-pipe system, lowering the temperature too far breaks the heat distribution.

Balancing the lockshield valves, the key almost nobody does

Even in a two-pipe system, a poorly balanced installation heats some radiators while leaving others lukewarm. Partially closing the lockshield valves on the radiators that heat up first redistributes the flow so they all warm up at the same time. On a single-pipe system the adjustment is even finer: if the first radiator is left fully open, the second runs cooler; if the first is closed completely, the second ends up hotter than the first. There is an intermediate point where both reach the same temperature, and that is the optimal setting.

How much you really gain with a conventional boiler

The small print in the specifications tempers the enthusiasm. In a conventional boiler, efficiency at 100% load with water at **70 degrees** is around **94%**, and at 30% load with water at **50 degrees** it rises to **96%**. Two points. That is the entire margin. The difference between a condensing boiler, which runs at **40-60 degrees**, and a low-NOx one, which runs at **70-80**, is not pure efficiency but circuit design.

Some argue that a heat engine's peak efficiency lies at an intermediate point between maximum and minimum, not at the extremes. The car analogy —burning more at 120 than at 100— falls short: raising the water temperature in a closed circuit is almost linear, whereas aerodynamic drag grows with the square of estimulante ilegal. The comparison doesn't hold up.

The PID thermostat and the cycling myth

The classic objection is that with very hot water the radiator stores so much energy that the house keeps warming up after the boiler shuts off. With water at **50 degrees** the temperature stays stable at **20 degrees**; with water at **60**, it swings between **20 and 21**. PID thermostats, which adapt the shut-off based on the heating rate, eliminate this problem: they never overshoot the setpoint, whether the water is at 40 or 80 degrees.

Practical experience points the same way. An oversized system at **60 degrees** heats a flat in **30-40 minutes** and the boiler doesn't restart for over an hour. And there are people who, after years with the water at **70 degrees** and damp problems on the walls, lowered it to **58** and, in the coldest months with frequent frosts, raise it to **66**: less consumption and less damp.

Steady temperature beats on-off cycling

Keeping the house at a stable temperature costs less than switching the heating on and off. If you let the home cool down, it then takes more energy to warm it up again. And if the boiler and pipework are inside the home, efficiency barely changes with water temperature: what changes is comfort.

In the end, the million-dollar question has a disappointingly simple answer. Turn the water down until the house stops feeling warm, and turn it up only when the outdoor thermometer drops. The rest is installer folklore.