Maximising Your Boiler’s Efficiency: A Guide to Flow Temperatures

Once your radiators are balanced, the most effective way to lower your energy bills is to optimize your boiler's flow temperature. By ensuring your gas condensing boiler operates in "Condensing Mode" as often as possible, you can significantly reduce gas consumption.

1. The Science of the "Dew Point"

For a condensing boiler to achieve its rated efficiency, the water returning from your radiators needs to be below 55°C. This is known as the "dew point," where the boiler can recover latent heat from the flue gases.

• Optimal Setting: Set your heating flow temperature to 60°C.

• The Logic: If you have balanced your radiators for a 12°C drop (Delta T), a 60°C flow ensures the return water is approximately 48°C, keeping the unit in its most efficient condensing state.

2. Finding the Right Controls

Most modern boilers feature a digital interface or dual dials to separate heating from hot water:

• Radiator Icon: This controls the "Central Heating Flow Temperature." This is the setting you should adjust for efficiency.

• Tap Icon: This controls the "Domestic Hot Water" (DHW) temperature for your sinks and showers.

3. Essential Safety Considerations

Before lowering your temperature, identify your system type:

• Combi Boilers (No Tank): You can safely lower the flow temperature to 55°C or 60°C. This does not affect the safety or temperature of your tap water.

• System & Conventional Boilers (With Cylinder): You must not set your flow temperature below 65°C. The water inside your storage cylinder must reach at least 60°C regularly to prevent the growth of Legionella bacteria.

4. Seasonal Adjustments

Efficiency is not a "set and forget" task; you can adjust based on the outside temperature:

• Mild Weather (Autumn/Spring): Try a flow of 50°C to 55°C. The radiators will feel cooler, and the house will warm up more slowly, but the efficiency gains are maximized.

• Extreme Cold (Mid-Winter): If your home struggles to reach the target temperature on your thermostat, increase the flow to 65°C or 70°C.

Efficiency Benchmark Table

Flow Temperature	Estimated Efficiency	Performance Notes
80°C	75% – 80%	Typical factory default; fast but highly inefficient.
60°C	90% – 95%	Recommended balance for comfort and savings.
50°C	98%	Maximum efficiency; works best with oversized radiators.

Expert Tip: Rather than cranking up the heat when you feel a chill, try setting your heating to come on 20–30 minutes earlier in the morning. Running your boiler for a longer duration at a lower temperature is significantly more cost-effective than a high-temperature "blast" of heat.