Heat

It's official: this has been the hottest weather in the Twin Cities in 11 years. We topped a hundred degrees today, and with the dewpoint in the 70's, it has been miserable. Worse, we've had a full week of this weather, and as the house heats up day after day it gets harder to keep it cool.

I've been trying to minimize our cooling costs by running the air conditioning as little as possible during the day, and turning it off when nobody's home. I've found, though, that the A/C needs to run a minimum number of hours each day just to remove the excess humidity--even if the temperature is comfortable, the moisture may not be.

The contrary is true, too. The temperature may be warm, but if the humidity is low enough we can tolerate it. In practice, that means I've been gradually setting the thermostat warmer and warmer throughout the heat wave, since the humidity drops faster than the temperature. At the beginning of the heat wave, I set it to 72 degrees overnight when the house was 78 in the afternoon when we got home from work.

Tonight, when we got home, the house was 87 degrees with a dewpoint of 66. I set the thermostat to 80, figuring that by the time the air is cooled to that point, the dewpoint will be down to 50 or so, and it will be reasonably comfortable.

What I really want is a thermostat which can be set for dewpoint instead of temperature. In the summer, keeping the dewpoint below 55 degrees is more important for comfort than keeping the temperature below 80.

The good news is that tonight should be the last night of the heat wave. The weather forecast calls for a low of 75 tonight and a 50% chance of thunderstorms, and a high of only 81 for tomorrow. After that, it's highs in the low 80's as far out as the forecast goes. As soon as the rain blows through, we'll be turning off the A/C, opening all the windows, and taking advantage of those wonderful nighttime temperatures in the low 60's. As heat-soaked as the house is, it might take a day or two to really cool off, but it will all be free, courtesy of Mother Nature.

Considering that the average hottest week of the summer is in mid-July, it is quite possible that we might not see 90 degrees again this year. On that happy note, I'll add that we're only six weeks or so away from the time to fire up the wood stove to stave off the chill of early autumn.