Yesterday it was 108. The saving grace is that the humidity was 13%. The swamp cooler worked admirably.  Inside it never got over 77.

Today, not so lucky. At 2pm it is 101 but the humidity is 26%. Inside it is 79 and over 60% humidity, comfortable but a bit sticky. I expect the day to get hotter for the next couple of hours. If it stays this hot, I’ll probably kick in the air conditioning in the master bedroom in the evening. I don’t sleep well if it is over 75. The master bedroom ac is an 8000 BTU unit that is good for a room up to 350 square feet, so the door and windows will be closed. The swamp cooler can handle the rest of the house. So far we have not wanted more than low fan and eco mode. We also have a 5000 BTU unit in the guest room.

Evaporative coolers work by keeping a pad wet and blowing air through it to cool the air off. When it is dry, that evaporated moisture does not go to waste. It increases the humidity inside the house which is very good for people with dry skin. Evaporating water absorbs a huge amount of heat. One liter of water evaporated at room temperature removes 2300 BTU of heat from the air. Two liters of water evaporated over an hour are as effective as my 5000 BTU unit. Twenty liters (6 gallons) per hour is equivalent to a small whole house unit.

Technically, ac units are rated in BTU per hour but nobody ever says or writes the “per hour” part. It just has to be understood. A BTU (English measurement) is fairly close to a kiloJoule (metric measurement) but we will stubbornly adhere to the obsolete system.

We probably only use 10 liters an hour, peak, because we are taking great pains to make our house energy efficient otherwise and we are more tolerant of heat. That is just a slow trickle into the cooler tank. Compared to our other water usage, it is small. Laundry, showers, washing dishes, irrigating what is left of our lawn.

In hot weather drink a lot more than you think you need. There is nothing wrong with soda, beer, wine, and coffee in moderation. That is an urban legend generated by speculation and not by actual tests. Actual research tells a different story. (Liquors are out. They definitely dehydrate you more than the water they provide.) Heat exhaustion and stroke can happen in a hot room to a vulnerable person. You don’t have to be working just underhydrated.

Hyponatremia is another hot weather legend. It comes from flushing your body with water before and during an athletic event.  (There are rare medical conditions and some drugs that can cause it too.) A normal diet has more than enough salt in it. Or drink a sports drink (or beer or coffee) occasionally or add a pinch of salt to every gallon of water.

Recognizing and Preventing Heat Stroke

One can become more comfortable with warm temps over time – and probably should. Certainly, if you want to spend time recreating outside it is a good idea to do so. People die out here on a regular basis from exiting their 68-72 degree workplaces, homes and autos and imagining they can be active in 100-degree weather without acclimating. Never mind when the power fails. Right now 90 degrees is still “hot” but by the end of August, that would be a cool day for me.

While evaporative cooling works well in low humidity, it farts out when the humidity starts to climb for the same reason a fan is less effective at cooling your body.  Humidity is a measure of what percentage of its total water capacity the air is at. The more water vapor in the air the less the water in a cooler wants to evaporate. Additionally, if the air is already at 60% humidity, increasing it to 80% with only a small drop in temperature isn’t going to help. For cooling in a humid area, you want powered ac, cold showers or to take regular dips in a pool.

Powered ac takes a refrigerant and compresses it. This causes it to become hot. This hot refrigerant is then cooled off in a radiator. Once cooled off, we decompress it which lowers it to a frigid temperature. Then that is used to cool air which is blown into the room by a fan. It functions best in high humidity. The vapor in the air allows for better heat transfer. The refrigerant is cold enough that water condenses inside the ac and runs out a drain.

Today most houses have central air, regardless of where they live. Ours is a 60-year-old house and we never felt the need to upgrade. Neither did the previous tenants. Central air costs several thousand dollars and is a horrible energy hog. Our summer electric bills are small. Four hundred to a thousand dollars a month are not uncommon for our neighbors.

Very recently, some of them have offset the cost of ac by installing solar panels. They have become the most energy efficient houses in the area. Another few thousand dollars to invest but if you have a high electric bill, it would be worth it. An added benefit is that the solar panels shade your roof so that your attic – and hence your house – don’t get uber hot to start with.

There are tricks to using an evaporative cooler. If you want to cool an area, open the window. The fan is forcing cool air into the house and it will go where it has a way out. If there is a strong wind, you might want to keep the windows on the upwind side of the house closed. A wind can overpower the pressure from the fan.

We keep the attic entrance open. After circulating thru the house, the air from the cooler is slowly forced up into the attic where it spreads out. Because cold air sinks and hot air rises, we now have a layer of cooler air in the attic while the hottest stuff exits out the vents.

Old people in old apartments have a very rough time of it over summer. You can always put on warmer clothes and blankets when it gets cold but when it is hot there is only so far to strip.

Should you have a supply of water, take cold showers. Lots of them. Wear cotton clothing and keep it wet. Opening a refrigerator is a temporary fix. It cools you off but generates much more heat. You have to stand right in front of it and it will make the rest of the apartment hotter. Shades down on the sunny side of the residence will obviously keep it cooler. A fan by itself may be all you need with these steps.

You can improvise a swamp cooler by with wet towels or sponges and a fan.  You can manually wet the towel. You don’t need drip tubes or aquarium pumps. Long ago, people without electricity would just hang wet towels over all their windows. The natural breeze would go thru the towels and cool off the interior. You have to keep rewetting them so a reliable water supply is needed.


Bedouins are the masters of hot and dry weather survival.


If you are in the sun, you will be most comfortable in light colored, very loose fitting clothes. Dress like a Bedouin. The cloth doesn’t act to keep the heat in. It is loose and flows easily with the slightest movement or breeze. This creates shade and not insulation. It allows for air movement which enhances evaporative cooling while an inner layer traps moisture close to the skin.

The light color also reflects heat and visible light- which in turn is absorbed and turned into heat. That is hundreds of watt-hours worth of heat energy you don’t need to deal with. If you aren’t dressed like a Bedouin, a lightweight, ventilated hat with a broad brim is the single most important thing you can wear. Shoes with a thick insole and socks to insulate you from the hot ground are the other.

If you are in shade and you have plenty of water, then wearing nothing at all is often the most comfortable. However, cotton clothing will absorb sweat which will keep it from evaporating as fast. That is a better choice in a survival sitiation. Wet cotton is man’s best friend when it hot.