You know the dog days of summer have come to Portland when Highway 26 is packed all the way to the coast and the Willamette River is covered in watercraft full of people seeking relief. Air conditioning is still a rare occurrence in Portland homes, and those lucky enough to have a basement know well its benefits!
What you may not know is that in this temperate climate, even the hottest days are usually followed by drastically cooler nights. It is not uncommon to see 25-30 degree shifts from day to night! A savvy homeowner can take advantage of this local phenomenon with the most rudimentary of habits to naturally cool their homes.
The moment of opportunity is when the outside temperature drops below the current indoor temperature of your house. This moment in time will change depending on how hot the day has been, and how many hot days have preceded it. A heat wave in late August may set you back to 10pm for opening windows! If you open a window and the air outside feels even slightly cooler, the time is right.
At this point, open every available window and door (even interior doors) from the top to the bottom of your house. If you have more than one story or a basement, it is especially important to allow airflow up through the structure from floor to floor, such as opening a door at the top or bottom of a stairway. Warm air in the house will naturally rise and escape out the top, drawing in cooler exterior air at the bottom.
This movement of air up through a building is called the “stack affect”. Any enclose space, no matter what size or shape, will have this same dynamic. The taller the structure, the greater the pressure that follows the arrows shown in the airflow diagram. Some people install a whole house ventilator fan, but with a few simple steps each evening as you go to bed, your house can be cooled naturally without installing a house fan or using any electricity!
We use this method with fans upstairs drawing the heat out until we go to bed. When we go to bed, we close and lock all downstairs windows and doors, and have the loft (second story) window fan blowing in across the open living room area below. This causes the cooler air to pool in the closed area downstairs all night while the upstairs bedroom fans continue pulling warm air out. We also turn our furnace fan on low to keep the air flowing throughout the house all night.
Cooling off the interior of the house this way typically will bring it down to about 71 or 68 when I get up in the morning, when I open it up downstairs until it gets about 73 outside or the sun starts shining in windows. That is when we close up the house tight for the day if it is going to be hot. Since we have south-facing windows, we block the sun from hitting them to keep it cooler. Vinyl windows have also made a huge difference compared to the aluminum framed windows we used to have.