Passive Heating… Arrgh!
We recently tried to register The Keep under Airbnb’s “Off-Grid” category. To our surprise, we were rejected. Apparently, we didn’t look “off-gridy” enough. I think they were expecting a hillside bunker with a rusty windmill and a kerosene lamp, rather than a luxury sandstone retreat. We had to explain that the nearest power pole is nearly an hour’s drive away—we’re definitely off-grid.
But being truly off-grid comes with its own set of “learning opportunities,” specifically when it comes to managing the temperature.
The Cactus Sanctuary
Like many sustainable builds, we rely on passive heating. It’s a beautiful system: the sun warms our massive sandstone walls, which then slowly releases that heat throughout the day. In theory, you just use the blinds to fine-tune the temperature.
Sue and I inherited this system and, for a while, we didn’t give it much thought—it just worked. That was until a few recent guests hinted that, at 30C +, the top floor was perhaps better suited to lizards and cacti. Aaarrrrgh! It was time to do some homework.
The “Autumn Overheating” Phenomenon
I discovered a phenomenon called Autumn Overheating. In summer, the sun is high and misses the bricks. In winter, the sun is lower and hits them directly to warm the house. But in Autumn, there’s a glitch: the sandstone still holds residual heat from summer, the sun is low enough to start baking the walls again, and the overnight temperatures aren’t quite low enough to offload that excess warmth.
For home owners the solution is easy, get the blinds down early and open the top floor windows, but it’s a tricky balance when you have guests on holidays.
The Great AC Dilemma
We’ve looked into air conditioning, but for an off-grid property, it’s a heavy decision:
• The Power Factor: AC is a power hog. While we have a diesel backup generator, we pride ourselves on running almost entirely on solar. Do we really want to fire up a generator just to cool down a house designed to be “passive”?
• The Guest Factor: The alternative is asking our guests to help manage the building’s “breathing”—getting blinds down early or creating a cross-breeze.
Over to You: Chore or Charm? Does being asked to manage the windows feel like a chore that gets in the way of your holiday? Or is that connection to the environment—knowing you’re keeping things cool using nothing but the breeze—part of the appeal? Would you prefer the effortless chill of AC, even if it meant hearing a generator kick in? We’re genuinely curious to hear your thoughts.
Autumn Tip: If you’re visiting soon, if it’s a bluebird day, keep those top-floor blinds down until the sun passes. Your evening self will thank you.
