The Generator & Power

One machine, in the boiler room, powers every light in the school. It starts each run at 62% fuel and 74% condition.

The fuel burn formula

Straight from the game's own comments: burn is deliberately transparent and additive rather than multiplicative, so the numbers stay legible. In fuel-percent per second, while the generator is running:

That raw total is then multiplied by 1 + min(9, night−1) × 0.10 for how deep into the run you are (up to ×1.9 by night 10), and during the day phase the whole thing is further multiplied by 0.6 (lights matter less in daylight, so the machine idles lower).

burnRate = (0.20 + 0.12×wear + 0.012×messes + 0.008×max(0, litRooms−4))
           × (1 + min(9, night−1) × 0.10)
           × (phase === 'day' ? 0.6 : 1)

Worked example

Night 5, generator at 50% condition (wear = 0.5), 3 messes left uncleaned, 6 rooms lit (2 over the free allowance of 4), at night:

raw = 0.20 + 0.12×0.5 + 0.012×3 + 0.008×2
    = 0.20 + 0.06 + 0.036 + 0.016 = 0.312 %/s
night scale = 1 + min(9,4)×0.10 = 1.40
burnRate = 0.312 × 1.40 = 0.437 %/s
A full tank (100%) would last 100 / 0.437 ≈ 229s ≈ 3m49s.

Compare that to a tidy machine on night 1 (100% condition, 0 messes, ≤4 rooms lit): burn rate is exactly the 0.20/s base, so a full tank lasts a clean 8m20s — roughly two and a half nights' worth on Normal difficulty. Per the developer's own comment: "a tidy school on a healthy machine with only the rooms you need switched on lasts roughly two and a half nights. Neglect it on every axis at once and a full tank barely covers one."

Wear and stalling

Condition decays at a flat 0.07 per second while the generator runs (doubled to 0.14/s during a Storm night), regardless of anything else — "about one spare part a day keeps it healthy," per the source comments.

If fuel hits 0% at any point, the generator stops immediately with "THE LIGHTS GO OUT" — no countdown, no warning beyond the "running dry" toast that appears whenever the estimated time left drops under 30 seconds.

Starting it

You can only pull the starter cord if fuel > 1% and condition > 12% (otherwise: "No fuel in it." / "Too broken to turn over."). Even then it isn't guaranteed: the start chance is clamp(0.35 + condition/140, 0.35, 0.98) — 35% at rock-bottom condition, rising to a capped 98% once condition passes about 88%. At the generator's starting condition of 74%, that's about an 88% chance per pull.

A failed pull ("It coughs and dies. Pull again.") makes a noise (level 0.7) and does not cost you anything except time — but after 3 failed pulls in a row, the next pull always succeeds, regardless of condition.

Refuelling and repairing

Each of these also triggers a roughly 28% chance of the Pokémon-card boy (the "Card Kid") turning up nearby — see Card Boy & the Taker.

Light switches and the fusebox

Every non-hallway room has its own light switch, toggleable for free (no hold time) — but it only actually lights up if the generator is running. The boiler room's fusebox resets every breaker in the school at once (1.6s hold), switching every room's lights back on in one go — useful after Bob has been through switching things off, but it burns fuel faster the instant it's done since more rooms end up lit.

Bob will physically switch a room's lights off as he leaves it, from night 2 onward (see Bob the Janitor). Grump, once turned, pops light bulbs near himself as he walks (roughly every 9–18 seconds), disabling that fixture for 25 seconds.

Portable lights

Your own private grid, independent of the generator:

Batteries also recharge your torch by +58% when used directly, and a Torch (flashlight) itself drains at 2.6% battery per second while switched on (5.2%/s on a Cold night).