Cut Your A/C Bill: Free Hourly Cooling Saver | Nowcast

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Open windows when outside ≤ °F<br>Close windows when outside drops below °F<br>Close windows when dewpoint above °F

What's a dewpoint, and what number should I pick?

Dewpoint is the temperature the air would have to cool to before<br>moisture starts condensing — it's the most honest measure of how muggy the air<br>actually feels (better than “% humidity,” which changes with temperature).

A rough comfort guide — pick the ceiling you'd still open the windows at:

≤ 55°F — dry and comfortable

60°F — getting noticeable, still fine for most

65°F — sticky; the default — good for most people

70°F — muggy / uncomfortable

75°F+ — oppressive, tropical

Above your number, we'll say “close up” even if the<br>temperature looks fine — open windows would just let damp air in. Lower the number<br>if you're sensitive to humidity; raise it if you don't mind it.

Show overnight window changes too (11 PM–7 AM)

Checked: you'll see every overnight open/close, even a brief one.

Unchecked (default): while you're asleep we won't flip you<br>“close then open” for a marginal dewpoint or temperature — a genuinely oppressive<br>night still says close.

Close windows when AQI >

Units

°F<br>°C

Expensive hours (optional — peak-rate / TOU window)

Hours when running A/C is unwanted — could be your utility's peak rates,<br>generator-fuel hours, off-grid battery-depletion window, anything. We'll suggest<br>"A/C off" during this range regardless of outdoor temp.

Example: some EV-friendly utility plans charge ~6× more during evening peak<br>(e.g. 6 PM – 9 PM) in exchange for cheaper overnight charging rates.

Starts<br>Ends<br>(Leave both blank to disable)

Season (optional). EV / time-of-use peak rates are often only part<br>of the year (e.g. summer). Set a month/day range and the peak-rate warning only<br>applies during that season — it repeats every year. A range like Nov → Feb wraps<br>across the new year. Leave blank to apply year-round.

From

To

Your electricity rates (optional) — add these to see your estimated<br>dollar savings from precooling.

Normal rate $ /kWh<br>Peak rate $ /kWh<br>A/C units

📍 Use my location<br>↻ Update forecast

Pick a spot on the map to begin.

How this works

Every hour, the tool pulls the current and forecast weather for the<br>location you pinned and asks five simple questions:

Is the outdoor temperature below your comfort target? (You set this — default 75°F)

Is the dewpoint reasonable, so opening windows won't make the house clammy? (You also control what counts as a good dewpoint — default 65°F)

Is the wind calm enough that windows won't slam shut or blow dust in?

Is air quality (AQI) safe to breathe?

No rain blowing in, no NWS advisory active?

If all five are yes, you should open your windows — that<br>hour gets a green block. If any one is no, you should keep<br>them closed — that hour gets an amber block with the specific<br>reason ("dewpoint 68°F — humid air" or "AQI 142 — smoke advisory").

💨 Tip: when it says open, opening more than one<br>window — ideally on opposite sides of the house — sets up a<br>cross-breeze and cools far better than a single open window.

The result is a 24-hour color-coded timeline. At a glance you know<br>when to open, when to close, and why. The "next change" banner tells<br>you the next time you'll need to act.

Why dewpoint, not relative humidity?

Relative humidity by itself is misleading. 60°F at 80% RH feels fine.<br>75°F at 80% RH feels swampy. Dewpoint measures the absolute<br>moisture in the air, independent of temperature. Above about 65°F<br>dewpoint, opening windows brings sticky air into the house — even<br>if the temperature seems comfortable. The tool blocks window-opening<br>on that threshold so you don't lose the dryness you've built up<br>indoors.

The "open all day" sweet spot

Mild days where outdoor stays below your comfort target for the<br>whole 24 hours are a free win — A/C off all day, windows open, no<br>work needed. The tool tells you "windows open all day" outright when<br>that applies. In dry climates this can happen 30-40 days a year;<br>in coastal mild climates, far more often.

Time-of-use rates change the math

If your utility charges more for electricity during certain hours<br>(a "peak rate" or "TOU window" — often 4-9 PM in summer), running<br>A/C during that window can cost 3-6× more than off-peak. The tool's<br>Expensive Hours control lets you mark those hours<br>so the timeline shows when to not run A/C regardless of<br>outdoor temperature — pre-cool earlier when rates are cheap, let<br>the house ride through peak, recover after.

This works for any reason A/C is "expensive": utility TOU rates,<br>generator fuel cost, off-grid battery depletion windows. The tool<br>is reason-agnostic — just mark the hours you want to avoid.

Air quality and wildfire smoke

The tool checks hourly US Air Quality Index (AQI) for your location.<br>When AQI exceeds 100 (the EPA's Moderate-to-Unhealthy crossover),<br>open windows...