Complete Guide to Preventing Heatstroke in Rental Housing — From Air Conditioning to Ventilation to Emergency Response

According to Fire and Disaster Management Agency data, approximately 80% of heatstroke deaths occur in residential settings (indoors). Beyond outdoor activities, the interior of rental properties is actually the highest-risk environment. Especially in households where elderly people, infants, or those with underlying health conditions live, appropriate measures can be lifesaving. This article brings you practical guidance from rental property professionals on preventing heatstroke indoors.

Why Heatstroke Occurs Frequently Indoors

The main reasons heatstroke develops indoors are as follows:

High Temperature and Humidity Indoors During Japan's summer (June–September), temperatures often exceed 30°C with humidity of 70–90%, and in rooms without air conditioning or with insufficient ventilation, the wet bulb globe temperature (WBGT) reaches dangerous levels.

Avoiding Air Conditioning Due to "Endurance" or "Energy-Saving Awareness" The mindset of "it's a bit hot, but air conditioning is wasteful" is dangerous. Fatal cases are particularly common among elderly people living alone who worry about electricity costs.

Rising Indoor Temperatures at Night Walls, ceilings, and floors absorb heat during the day, and on "tropical nights" when indoor temperatures remain high even after sunset, body temperature can rise unnoticed during sleep.

How to Reduce Heatstroke Risk When Choosing a Rental Property

Check Building Age and Insulation Performance Properties with poor insulation performance (especially wooden structures without reinforced concrete that are over 30 years old) tend to have higher indoor temperatures in summer.

• •Window count and direction: Many south-facing or west-facing windows mean strong sunlight and higher summer temperatures
• •Top floors and rooftop levels: Upper floors are difficult to cool due to radiant heat from the ceiling
• •Availability of ventilation windows: Having windows on diagonal sides allows good air circulation

Verify Air Conditioning Equipment Always verify during a property viewing whether air conditioning is installed or can be installed:

• •Air conditioning included: Verify outlet type (200V/100V) and capacity (horsepower)
• •Air conditioning installation possible: Verify the location of wall holes, sleeves, and 100V/200V outlets
• •Installation not possible: Spot coolers (evaporative air conditioners) have limited cooling effectiveness, so this is high-risk

Heatstroke Prevention Strategies for Rental Housing (Practical Edition)

Basics of Room Temperature and Humidity Management

Guidelines for heatstroke-safe temperatures:

• •Maintain room temperature at 28°C or below and humidity at 60–70% or below
• •WBGT 28 or above is "Severe Caution," 31 or above is "Danger"

Correct use of air conditioning:

• •Set temperature at 28°C (ideally with a 10–15°C difference from outdoor temperature)
• •Use a fan together with air conditioning to prevent illness from overcooling
• •Use "auto mode" or "timer function" while sleeping
• •Pre-cool the room before arriving home using smart remote controls or air conditioning timer functions

Ventilation and Heat Blocking Measures Beyond air conditioning alone, use physical heat-blocking measures to prevent indoor temperature from rising:

• •Blackout curtains and blinds: Block direct sunlight from west-facing and south-facing windows (can lower room temperature by 2–4°C)
• •Green curtains (bitter melon, morning glory): Plants on the outside of balconies or windows block sunlight. Can be installed on railings even in rental properties
• •Sprinkling water outside windows: Spray water on sidewalks or gardens in early morning or evening (avoiding hot midday) to lower temperature
• •Reverse-running ventilation fans: Running kitchen exhaust fans in reverse at night to expel indoor heat (varies by model)

Water and Salt Replenishment The foundation of prevention is maintaining adequate body hydration:

• •Aim for 1.5–2 liters of water per day
• •When sweating heavily, also replenish salt and minerals (sports drinks, salt tablets)
• •Alcoholic and caffeinated beverages have diuretic effects, so reduce intake on high-risk heatstroke days
• •Always hydrate upon waking, before going out, and before/after bathing

Residents and Situations Requiring Extra Caution

Elderly People Living Alone This is the highest-risk group due to the combination of reduced heat sensitivity with aging and an "endurance" mindset. Regular check-ins and visits from family or neighbors are crucial.

Households with Infants and Children Risk is higher than for adults because temperature regulation is underdeveloped. Pay special attention to room temperature management during naps and sleep.

After Work or Exercise After moving, balcony work, or indoor cleaning, body temperature is elevated, so don't forget cold water, rest, and cooling.

During Power Outages and Air Conditioning Failure During power outages from typhoons or disasters, or when air conditioning breaks, perceived temperature spikes sharply. Keep portable fans, cooling packs, and ice on hand as emergency cooling methods.

Emergency Response When Heatstroke Occurs

If heatstroke symptoms appear indoors, immediately follow these steps:

Identifying Symptoms

First Aid Steps

1. Move to a cool place: An air-conditioned room or shaded, well-ventilated area
2. Loosen clothing: Cool the neck, armpits, and groin area (where large blood vessels are) to help dissipate body heat
3. Replenish water and salt: Only if conscious (do not give if unconscious due to aspiration risk)
4. Cool the body: Apply cooling packs, wet towels, or ice to the neck, armpits, and groin
5. If unconscious or unresponsive: Call 119 immediately

When to Call an Ambulance

• •Unconscious or not responding to calls
• •Seizures occurring
• •Body temperature over 40°C
• •Unable to drink water on their own

"Wait and see" is strictly forbidden. In severe cases, life can be at risk within minutes.

Heatstroke Prevention Products for Rental Properties

Here are heatstroke prevention products suitable for rental properties where you must restore the original condition upon moving out:

Summary: Taking Action When You Feel Hot Can Save Your Life

The best prevention for indoor heatstroke is not to endure it. Use air conditioning appropriately, manage room temperature and humidity, and make regular hydration a habit.

High-risk groups are especially "elderly people living alone," "households with infants and children," and "properties without or with broken air conditioning." When choosing a rental property, also verify summer livability (insulation, sunlight exposure, and air conditioning equipment) as an important factor, and realize a comfortable and safe summer living experience in your rental home.

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