The world is warming, putting more people at risk of extreme heat events and stressing societies already grappling with other effects of climate change. Unfortunately, temperatures are climbing every year, and heat waves are becoming more common and longer lasting. This has a huge number of negative effects on humans. In fact, extreme heat is the deadliest of all natural events, more than twice as deadly as hurricanes and tornadoes combined. They’re expensive, too, with one estimate putting the health care costs alone at $1 billion each summer.
So what can homeowners do to prepare? Is your home at risk? How will temperatures change in your neighborhood?
To help current and future home searchers understand the impact of climate change on extreme heat, Redfin has partnered with climate nonprofit First Street to show the Heat Factor® for every property on Redfin.com. Heat Factor® builds off of decades of peer-reviewed research to show the current and future extreme heat risks for every home, city, and county so homebuyers and homeowners have all the information they need when deciding where to live.
Heat Factor® uses the First Street Extreme Heat Model to determine a specific location’s exposure to extreme heat events based on surface temperature, topography, land cover, and relative humidity. The model also takes into account “local hot days”, or the hottest seven days in a year for a given area, and how they are expected to change due to climate change. Heat Factor® is available for any location in the contiguous United States. More information can be found on the Risk Factor™ website.
Heat Risk Frequently Asked Questions
What is a heatwave?
What causes a heatwave?
Air becomes trapped when a high-pressure system forces air downward, preventing air near the ground from rising. The downward air pressure acts as a cover and traps warm air in place. When air can’t rise or follow a normal eastward cycle, the temperature continues to rise, causing a heatwave. The longer the high pressure is in place, the longer the heatwave. Heatwaves are generally associated with diminished air quality, drought, and other societal strains..
What is the heat index?
For example, a temperature of 90ºF may not sound very hot, but if the relative humidity is 70% (which is not uncommon in places like Miami), the air will actually feel closer to 106ºF. The NWS would categorize this as dangerous for human health.
Interestingly, because humidity is critical to the heat index, dry and hot locations can have a heat index lower than the air temperature. For example, in Phoenix, a 110ºF day may actually feel like 108ºF if the relative humidity is 15%. This is why places with the outright hottest temperatures may not pose the greatest risk to human health (but can still be dangerous). Heat and humidity combined are the most dangerous.
How hot is too hot inside of a house?
If your home is at 95˚F or above, do not use a fan to cool yourself down; blowing hot air will stress your body further and more quickly.
High temperatures can damage your property as well. When the temperature inside creeps above 80˚F, the refrigerator and stand-alone freezer run hotter, and air conditioning systems need to work more to keep the house cool. A reasonable temperature target for people and property is between 68-75˚F.
What’s the hottest temperature humans can survive?
It was long believed that 95ºF at 100% relative humidity was the upper limit of human tolerance, which gives a heat index of 161ºF. However, new research has shown that it’s actually much lower. Many locations in the hot and humid Persian Gulf have surpassed this new threshold, most recently Asaluyeh, Iran, which recorded a temperature of 92.7ºF at 100% humidity. To residents in Asaluyeh, this felt like 147ºF.
What’s the hottest temperature ever recorded in the U.S.?
What are the hottest cities in the U.S.?
1. Honolulu, HI
2. Miami, FL
3. Brownsville, TX
4. Yuma, AZ
5. West Palm Beach, FL
6. Phoenix, AZ
7. Fort Myers, FL
8. Tampa, FL
9. Orlando, FL
10. Corpus Christi, TX
These cities see warm temperatures year-round and are often popular tourist destinations. All of these cities also have a very high Heat Risk® (except Honolulu, which isn’t included in Heat Risk® data).
How do you keep your house cool in extreme heat?
- Start by keeping the sun out using shades, blinds, or tinted window film.
- Install an air conditioner, or if possible, a central air system.
- Set your ceiling fans to rotate counter-clockwise, which will blow the air down and cool the room.
- Use LED light bulbs throughout your home, which give off less heat than traditional bulbs.
- Unplug any unnecessary appliances, as anything plugged in emits small amounts of heat.
- Use a dehumidifier, which will filter the water out of the air and keep your home more comfortable during a heatwave.
How do you protect your home from extreme heat?
Start by investing in better insulation for your doors, windows, and walls to keep the heat out and the cool air in during the summer. In the interior of your home, be sure to always vent hot air out, whether that’s in your kitchen, bathroom, or laundry room.
For the exterior, place an awning or shade on the outside of your house to block the worst of the rays from your windows. You can also plant trees and bushes outside the windows that will soak up heat and provide you with welcome shade (making sure to keep them at least five feet from your house). To keep your roof cool, replace your shingles with a lighter color option that reflects light. Or to save money, consider painting the singles a light color instead.
Looking for more tips? Learn additional tips to heat proof your home.
What effect does extreme heat have on your home?
Foundation: Soil around a foundation will shrink as the ground heats up, and the moisture will evaporate. This causes soil to separate from the footing, potentially damaging to the foundation. This is especially pronounced during a drought.
Roof: During an extended period of high temperatures, a roof can expand and warp. This causes shingles to crack, making them more likely to leak when it rains or snows. Caulking around the flashing can also dry out, weakening the roof’s structure.
Attic: Attics often lack good airflow. As such, an attic is usually the hottest and most humid part of the house. Excess moisture and heat under the roof can cause roof shingles to deteriorate at an accelerated rate. Your attic can also develop mold.
Floors: Wooden floorboards can warp or expand from humidity that often accompanies extreme heat, causing shifting and creating uneven surfaces.
Pipes: Pipes can leak or break during periods of high water usage. When it’s hot, homeowners are more likely to use a hose, run a sprinkler or fill a swimming pool. This heavy water volume can damage pipes if they are poorly sealed.
Electric: High temperatures and electrical overuse can cause electric surges, outages, and even fires.
The Top 10 U.S. Cities Most at Risk of Extreme Heat
Rank | Metro | Share of Properties With a High Heat Factor® Risk | Total Properties With a High Heat Factor® Risk |
---|---|---|---|
1 | Houston, TX | 100% | 2,447,456 |
2 | Phoenix, AZ | 100% | 1,819,774 |
3 | Dallas, TX | 100% | 1,565,914 |
4 | Tampa, FL | 100% | 1,162,853 |
5 | Charlotte, NC | 100% | 1,092,145 |
6 | New Brunswick, NJ | 100% | 1,084,371 |
7 | Baltimore, MD | 100% | 1,008,581 |
8 | Orlando, FL | 100% | 941,082 |
9 | San Antonio, TX | 100% | 940,623 |
10 | Fort Worth, TX | 100% | 842,983 |
*“High risk” is defined as a property having a Heat Factor® of 5 (major) or higher. Since 304 metros have 100% of properties at risk, table is sorted by total properties at risk.
This page is for informational purposes only and is not a substitute for professional advice from a medical provider. Consumers should independently verify any claim, agency, or service mentioned. Learn more about our Editorial Guidelines here.
Additional Heat Risk Resources
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