In the Bay Area, when a heat wave hits, it hits hard. Most people do not have air conditioning since it’s not often needed. The summers are typically cool and our heat spikes are random days (though more frequently and more intense than even a few years ago).
Keeping the house cool during these events is a challenge but there are some tips to help.
Tip 1: Capture the cool nighttime air
This past week, in San Francisco in Noe Valley (our neighborhood), the daytime temps have hit the mid 80s, while most nights have gotten down into the 50s. When the outside temperature goes below the indoor temperature, open up the doors and windows. This lets the warm air in your house escape and get replaced with the cool outdoor air.
Tip 2: Close up when it gets warm
Overnight, hopefully you were able to cool down the house some with that marine layer. The key now is to keep it in your house as long as possible.
While the outdoor temperature is below the indoor temperature, keep windows and doors open. But, when the outside gets warmer than the inside, close them. This separates your cooler air in your house from the warming air outside. It will still gradually warm throughout the day, with heat coming through the walls and the ceiling and sunlight coming in through windows.
Tip 3: Use fans to keep people cool, not rooms
The key distinction is thinking of fans as cooling people, not rooms.
Fans simply move air around. But the cooling that we feel is that the air pushes the warm air away from our skin and evaporates sweat. It’s the movement of air across our skin that keeps us cool.
So point fans at people (or if using a circulator, point it high up a wall and let it move all the air in a room), but turn fans off in empty rooms as the fans themselves generate a small amount of heat.
Tip 4: Keep south-facing windows covered
The sun radiates heat and south-facing windows can be the biggest source of warming. Sunlight pours through these south-facing windows and this heat gets absorbed into the air, walls, floors, and furniture.
By covering them and keeping these windows as dark as possible, you can cut off a big source of incoming heat.
Tip 5: Don’t make A/C work harder than it has to
If you are lucky enough to have some sort of air conditioning, make its job as easy as possible. If there are rooms or floors of your house that you don’t need to keep as cool, close them off while your A/C is running.
Tip 6: (Geeky version) Automate as much of this as possible
I happen to have a weather station on our roof and thermostats throughout the house that report the temperature for various rooms. I use Home Assistant to tell me when the outdoor temperature goes above or below various indoor temperatures so I know when I should be closing and opening windows. It is absolutely not necessary but getting push notifications about those events helps keep me on top of the heat situation.
If you don’t have an outdoor thermometer, using wunderground’s wundermaps is a great alternative. The Bay is a collection of microclimates and these maps way more accurate than whatever your weather app returns. For example, in Noe Valley, there is often a 10 degree spread between what Apple/Yahoo returns for ‘Noe Valley’ and what mine and my neighbors’ weather stations are reporting due to the elevation and thermal inversion.
Tip 7: Stay hydrated
And, of course, stay hydrated with water, or whatever your beverage of choice may be.