Why Keeping Your Home at 19°C May Be Doing More Harm Than Good

Keeping homes at a steady 19°C (66°F) has been considered the gold standard for energy savings for decades, but 19°C is a number that was not designed for comfort or health. It was developed during a time of crisis in the 1970s, and it has stuck around far beyond the time it was actually useful. With today's modern building standards, better insulation, and the latest research, we can say that a slight increase in the temperature of indoor air in the range of 20 - 21 °C (68 - 70 °F) is a better balance of comfort, health and efficiency.

First Era: Crisis Standard

The beginning of the 19°C rule started from the 1973 oil embargo. It was a time when governments were trying to cut down the amount of fuel used. With oil prices increasing, households were encouraged to reduce their heating for the sake of conservation, which was a practice seen in many countries and one which later the U.S. Department of Energy adopted in guidelines.


During that time the energy efficiency of homes was not nearly at the standards we have now. With the use of single-pane windows, insulation, and cheap heating systems, energy-efficient homes were not going to be something that people had. Energy specialist Nick Barber, speaks about the guidelines of the time and says, “It was never about comfort-it was about economics.” It was out of place for the time and the lapse of time for the guideline only demonstrates that.

Scientific Evidence: What Modern Research Says

Current studies have raised substantial concerns with the 19 °C rule. Most notably, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, through ASHRAE Standard 55, have published their guidelines on indoor comfort. Their range shows comfort in the winter between 20 °C and 24 °C. This is in stark contrast with the 19 °C rule being suggested.

One of the landmark studies is titled, “Thermal comfort in naturally ventilated buildings: revisions to ASHRAE Standard 55.” Researchers, Richard de Dear and Gail Brager, have analyzed 21 000 data points from 160 buildings across 4 continents. This research is the first to introduce the adaptive comfort model. Modern, well-designed buildings result in occupants wanting much warmer temperatures.

U. S. Department of Energy also encourages 68 °F (20 °C) as the optimal winter temperature. However, they also state that settings any lower than this would cause more strain on the heating system than any other level.

Health Implications of Colder Homes

Staying at home and maintaining an indoor temperature of 19 °C can result in some serious health issues, even aside from comfort. Research titled, “Cold indoor temperatures and their association with health outcomes,” studied 20 studies and analyzed the links between colder indoor environments and increased risks of cardiovascular disease, respiratory problems, and the quality of sleep. This review still remains the most recent systematic review in the journal Public Health.

WHO recommends indoor temperatures of 18°C (64°F) and above for the sake of vulnerable groups like the elderly, those with chronic illnesses, and patients with cold-stressed bodies. Cold temperatures can increase stress and cause blood pressure to rise, as well as weaken one’s immune defenses.

Heating professional Brad Roberson says that a sufficiently warm temperature can prevent a “constant edge of cold,” and promotes better productivity and well-being. This is is especially true with the work-at-home trend we are seeing as a result of the pandemic.

The Hidden Costs of Underheating

It may seem like lowering the temperature for heat would save energy, but that is not the case. HVAC expert Josh Mitchell warns that maintaining a temperature of 66°F can lead to condensation, mold, and cause damage to the heating system in a newly modern sealed house.

In fact, heating systems create artificially low comfortable temperatures causing the system to work in short, rapid cycles. Heat systems wear out faster this way. Increased energy expended and decreased comfort are proven in the studies performed by ENERGY STAR. Additionally, they show that setting smart thermostats within the 68°F ballpark increases energy savings of 5-10% especially when used in conjunction with zoned heating and humidity control.

Neil Stephens, an expert in building science, argues that indoor temperature settings should not be simplified into one number, as comfort is influenced by many variables, including the construction features, moisture, and how air is distributed in the space.

Contemporary Guidelines for Today’s Residences

Due to high-quality insulation and temperature control systems, modern homes allow for an increasing range of daytime indoor temperature flexibility. Experts suggest a range of 20-21 °C (68-70 °F) as an optimal temperature range, while it’s also generally acceptable to allow indoor temperatures to drop to 16-18 °C (62-65 °F) at night or during periods when the space is unoccupied.

This type of control is indicative of the increased sophistication of building systems and construction science, as well as the growing body of research in regards to human comfort. This is also consistent with adaptive comfort theories, which state that individual comfort levels vary based on personal circumstances, as well as the environmental conditions.

Final Thoughts: The Need for Customization

The 19 °C rule is a modern day artifact from an energy crisis that has been a defining feature of an adjacent era in building science. The 1970’s energy crisis has passed, and now the findings from modern research, particularly those from ASHRAE and the U.S. Department of Energy, demonstrate that indoor temperatures that are slightly above the norm of 19 °C clearly improve comfort, health, and are more energy efficient over the long-term.

Homeowners ought to move on from rigid and outdated guidelines, to formulate a more balanced strategy that encompasses elements other than just energy savings, but also considers modern day living and well-being.