PorchWeather: Know when to open your windows

Aug 28, 2026

Back in 2022, I wrote a post about my home automations. My favorite one on the list was the simplest sounding: a notification telling me when to open or close the windows. I ended that section with this:

I've been thinking about making a website where anyone can register for these kinds of alerts by entering a zip code or lat / long, as well as a phone number to text when it's time to open or close the windows. I don't know if I'll actually do this though.

Well, four years later, I actually did it: PorchWeather.com. You tell it where you live and what conditions you consider window-worthy, and it emails you or pings your phone when it's time to open up, and again when it's time to close.

Why this automation stuck

In the Bay Area, the summer weather pattern is remarkably consistent: warm to hot afternoons, then cool evenings once the marine air moves back in. On most summer days, the outside air is cooler than my house from the evening until mid-morning. If you open the windows during that stretch and close them before it heats up, the house coasts through the hot part of the day on the cool air you banked overnight. It's air conditioning, except the compressor is the Pacific Ocean and it's free.

The trick is timing. Open too early and you're letting in hot air. Forget to close in the morning and the house warms right up with the day. And the temperature isn't the only thing that matters: sometimes it's cool out but the air is full of wildfire smoke, a real hazard around here in the fall, or it's windy and unpleasant, or the humidity is off enough that the cool air isn't worth it.

So for years I ran this as a Home Assistant automation. It watched a local weather station for temperature, wind, rain, and humidity, watched nearby air quality sensors for particulates, compared against the indoor temperature from my thermostat, and sent a phone notification when the air outside was better than the air inside. When conditions flipped, it sent another notification to close things up.

What I liked about it then is still what I like about it now: it's almost a software-only automation. No motors, no smart vents, no hardware to install. The human is the actuator. It just turns out that the hard part of "open the windows at the right time" was never opening the windows, it was noticing the right time.

From automation to website

The problem with a Home Assistant automation is that it only helps people who run Home Assistant, and realistically only people who enjoy fiddling with YAML. The idea itself needs none of that. All of the inputs are public weather data. There's no reason my neighbor should need a home server to get the same notification.

So PorchWeather is that automation, rebuilt as a service anyone can use. You add a location by dropping a pin on a map, then set your conditions: a comfortable temperature range, and optionally limits on humidity, wind, chance of rain, dew point, and air quality. A worker re-checks the weather for every active location every ten minutes, and when your conditions become true it notifies you that it's window time. When they stop being true, it tells you to close up.

A few details took more thought than I expected. Weather wobbles around thresholds, so there's hysteresis to keep it from telling you to open and close the windows five times in an hour, the same debouncing trick I needed for my backyard gate sensor years ago. There are quiet hours, since a 5am "it's nice out!" push notification is a good way to get unsubscribed. And the notification direction is configurable, because some people only want the "open" nudge and are perfectly capable of noticing when it gets hot.

For the weather data, I self-host an instance of Open-Meteo, which reads model output directly from the public open-data archives. For locations in the contiguous US, that means NOAA's HRRR model at 3 km resolution, updated hourly, with a global ECMWF model covering everywhere else. One of the quiet wonders of the modern internet is that this data, a running physics simulation of the entire atmosphere, is just sitting in a public bucket, free for anyone to build on.

Give it a try

If you live somewhere with a real daily temperature swing — most of the western US, but plenty of other places too — this is the kind of thing that saves you money on cooling while getting fresher air in the house than any AC will give you. And if you live somewhere muggy, the dew point condition can tell you about those rare crisp days worth throwing the windows open for.

It's free, and there's no catch. This is a hobby project that escaped the house, not a startup. If you try it and something doesn't work, or the notifications fire at times that seem wrong for your area, I'd genuinely like to hear about it.

PorchWeather.com

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