For decades, we’ve been told that 20°C (68°F) is the “magic number” for a comfortable, efficient home. It’s the standard setting found in most manuals and government advice. However, as energy costs remain a top priority this January, heating engineers are challenging this old-school rule. A new consensus is emerging among thermal experts: there is a specific temperature—just slightly lower than the standard—that maximizes heat retention without sacrificing comfort. If you are still sticking to the 20°C rule, you might be overpaying by as much as 10%.
Highlights
- 📉 The 18.5°C Pivot: Experts now suggest 18.5°C is the optimal balance for the human body and the home’s thermal mass.
- 🔥 The Boiler ‘Cycling’ Trap: Pushing for 20°C often forces boilers into frequent on/off cycles, which wastes more gas than a steady, lower heat.
- 💧 Humidity Control: This specific temperature helps maintain a healthy 40-60% humidity level, preventing both dampness and dry skin.
- 💰 Compound Savings: Lowering your thermostat by just 1.5 degrees can reduce annual heating bills by over €150 on average.
Expert Tip: Your walls act like a battery. Once they absorb heat at 18.5°C, they radiate it back slowly. Forcing them to reach 20°C requires an exponential increase in energy that often leaks through windows before you even feel it.
Why the 20°C Rule is Outdated
The “20-degree rule” was established in an era of cheaper energy and less efficient insulation. In a modern context, aiming for 20°C often results in “overshoot,” where the heating system works at maximum capacity to hit a target, only to have the heat dissipate through ventilation. Heating experts point out that the human body barely perceives the difference between 19°C and 20°C when dressed appropriately, but your boiler perceives it as a massive increase in workload. By settling at 18.5°C, you hit the “plateau” where the home stays warm with minimal effort from the burner.
How to Transition Without Feeling the Cold
The key to success isn’t just turning the dial down instantly. It’s about managing the “Thermal Envelope” of your home. Experts recommend the following 20-minute adjustment strategy:
- The Half-Degree Drop: Lower the thermostat by 0.5°C every two days. This allows your body’s metabolism to adjust and the home’s structure to stabilize its heat retention.
- Focus on ‘Heat Bridges’: Ensure curtains are tucked behind radiators and sofas are at least 10cm away. At 18.5°C, air circulation is more important than raw heat.
- The Evening Buffer: Set the heating to turn off 30 minutes before you go to bed. The residual heat in the walls will keep the house at 18°C well into the night.
Frequently Asked Questions
1. Is 18.5°C safe for the elderly or children?
For healthy adults and older children, yes. However, for those with specific health conditions or infants, the World Health Organization still suggests a minimum of 20°C. Always prioritize health over savings.
2. Won’t my house get damp at a lower temperature?
Actually, keeping a steady 18.5°C is often better than “burst heating” to 21°C. Steady warmth keeps the surfaces of your walls above the “dew point,” which is what actually prevents condensation.
3. Should I leave the heating on all day at this temperature?
Only if your home is very well insulated. For most, it is still more efficient to heat the home only when needed, but using 18.5°C as your peak rather than 20°C.
Independence from high energy bills starts with a nuchter (down-to-earth) look at our habits. We don’t need to sit in the dark in a coat, but we do need to stop chasing an arbitrary number like 20°C just because “that’s how we’ve always done it.” By embracing the 18.5°C sweet spot, you protect your bank account and your boiler in one simple move.
Stay warm and stay smart.
