The number you hear most for winter indoor temperature is 18°C. But the same number points opposite ways in two documents. The WHO Housing and health guidelines propose 18°C in the cold season as a floor that protects health, while Korea’s Regulation on Promoting Rational Energy Use in Public Institutions caps public-sector heating at an average of 18°C or below. Both originals were read side by side.
1. WHO: 18°C as a safe and well-balanced indoor temperature. The recommendation that indoor temperatures be high enough to protect residents from cold is a strong one.
2. Older people, children and people with chronic illness may need it warmer than 18°C. Especially with heart or respiratory disease.
3. Korean public institutions: heating at an average 18°C or below, cooling 28°C or above. Hospitals, childcare centres and elderly care facilities, among others, may set their own.
WHO Housing and health guidelines — low indoor temperatures
- Recommendation (strong) — indoor housing temperatures should be high enough to protect residents from the harmful health effects of cold.
- For general populations in temperate or colder climates, 18°C has been proposed as a safe and well-balanced indoor temperature during cold seasons.
- A higher minimum than 18°C may be needed for older people, children and people with chronic illnesses, particularly cardiorespiratory disease.
- Recommendation (conditional) — in climate zones with a cold season, efficient and safe thermal insulation should be installed in new housing and retrofitted in old housing.
The WHO guideline uses 18°C as a floor — do not go below it (our reading). Last winter’s cold-related illness figures are in cold-related illness last winter.
The public-institution regulation — article 14, appropriate indoor temperature
| Item | Rule | Basis |
|---|---|---|
| Heating | Average 18°C or below | Art. 14(1) |
| Cooling | Average 28°C or above | Art. 14(1) |
| Mostly non-electric heating and cooling | Average standard may be relaxed within 2°C | Art. 14(2) |
| Personal heaters | Not to be used during working hours (09:00 to 18:00) — exceptions such as pregnant or disabled staff with the head’s approval | Art. 14(3) |
Article 14(1) lists eleven kinds of facility that may set temperatures flexibly by their own committee’s decision — facilities used by many people such as schools and libraries (office space excluded), medical institutions, child-related facilities such as daycare centres, and elderly welfare facilities, art galleries and server rooms, public transport facilities, training centres and dormitories, among others. The places where the people the WHO says may need more warmth stay are among the exceptions (our reading of the two side by side).
Same number, opposite directions — our summary
| Document | What 18°C means | Applies to |
|---|---|---|
| WHO Housing and health guidelines | A floor for health (at or above) | People in homes |
| Public-institution energy regulation | A cap for saving energy (average at or below) | Public-sector buildings |
The public-institution regulation does not apply to homes. No legal standard for home heating temperatures was found this time.
How heating bills bunch into winter is shown in the city gas bill calculator.
Checklist
- ☐ Does the home stay at or above 18°C? (WHO)
- ☐ Warmer if older people, children or people with heart or lung disease live there
- ☐ Consider better insulation in an older home
- ☐ The public-sector 18°C-or-below rule is for office space; medical, child and elderly facilities are exceptions
Questions that remain
Does the WHO set an upper limit?
The chapter read here covers low indoor temperatures. The chapter on high indoor temperatures was not read.
What about while sleeping?
Neither document gives a temperature for sleep.
The NHS says cold weather can also make dandruff worse — shampoo ingredients and the 4-week rule are in choosing a dandruff shampoo.
The NHS lists long periods in air-conditioned or heated rooms as a dry eye risk and suggests a humidifier (dry eyes).
The NHS lists people living in cold homes and older people living alone as most at risk of hypothermia (hypothermia).
Sources
- WHO Housing and health guidelines (2018), Chapter 4 — Low indoor temperatures and insulation — original (NCBI Bookshelf) (checked 12 October 2026). The strong recommendation, 18°C, older people, children and chronic illness, the conditional recommendation on insulation.
- Regulation on Promoting Rational Energy Use in Public Institutions [in force 30 April 2026] [Ministry of Climate, Energy and Environment Notice No. 2026-111] — original (checked 12 October 2026). Article 14(1) (18°C or below, 28°C or above, eleven exceptions), (2) (2°C), (3) (personal heaters, 09:00 to 18:00).
- Not read. The WHO chapter on high indoor temperatures; any Korean standard for home heating.
- Our reading. Setting the two 18°C figures side by side as a floor and a cap.
Where to check further
- A thermometer at home — the actual temperature of the rooms you live in.
Written 12 October 2026. The content sets out the WHO guideline and the Korean notice; setting them side by side is ours.