The Verification Venue · a summer life-hack, run through the first law
The Machine That Warms What It Cools
It's a heat wave, the AC is broken, and someone suggests propping the freezer open. It feels like it should work: a fridge makes cold, doesn't it? But a fridge doesn't make cold. It moves heat, and with the door open it moves that heat in a circle inside one room, while the motor quietly adds more.
Stand right in front of the open door and yes, you'll feel a cool draft. That part of the fear is real. But close the room up and wait, and the thermometer on the wall does only one thing: it climbs. A refrigerator is a pump that carries heat from a cold place to a hot place. Aim both ends into the same room and nothing leaves: you've just added a space heater that costs whatever the compressor draws.
Below is that room's energy budget, live. Set the compressor's wattage and its efficiency, then throw the one switch that separates a useless open fridge from a working air conditioner: where the hot coil points.
Net heat added to the room
+150 W
the room gets warmer
Sealed-room trend (40 m³ air)
+11.2 °C/hr
idealised upper bound: see the check
A typical household fridge draws ~100–250 W while the compressor is running. Door shut it cycles on ~⅓–½ the time; door open it runs almost continuously.
Heat pumped per watt of work. Watch the surprise: in fridge mode, dragging this does nothing to the net: a fancier fridge shuttles more heat around but still adds exactly +W. COP only bites once the hot coil is outside.
The whole thing is one line of bookkeeping. Every watt the cold coil pulls out of the cold side (Qc) plus every watt the compressor puts in (W) has to come out the hot coil (Qh). Energy can't vanish:
Both coils are in the room, so Qc and Qh both land here; they cancel, and what's left over is the compressor's own work, W. That's why the leftover is independent of COP: a more efficient fridge makes both Qc and Qh bigger by the same amount, and the gap between them stays exactly W.
The same machine, one coil out the window
An air conditioner isn't a different device. It's this exact refrigerator, turned so the hot coil hangs outside. Now Qh (and the compressor's W) leave the room entirely, and only the cold coil's Qc stays behind, as a removal. The room's net becomes −Qc = −COP·W. Flip the toggle above and watch the ledger's two "into room" tags turn to "outside," and the leftover flip sign. This is the only reason cooling ever works, and it's the moment COP finally matters.
The check: every number, recomputed live
Nothing here is asserted. From your two sliders, the page computes the whole ledger straight from Qh = Qc + W and shows its work:
The two independent ways this must agree: (1) the first-law identity Qh − Qc = W, and (2) a COP sweep in fridge mode: the net stays pinned at +W for every efficiency. Press the button to run both in your browser:
The °C/hr figure is the one deliberately idealised number: it assumes a sealed, perfectly-insulated 40 m³ room and heats only the air (ρ·V·c = 1.2·40·1005 ≈ 48.2 kJ/K), so it's an upper bound on how fast a real room warms; real walls, furniture and leaks absorb heat and pull the room toward a warmer equilibrium instead. The direction (always up in fridge mode) and the net watts are exact; the rate is illustrative. Run it offline too: node research/can-a-fridge-cool-a-room/verify-can-a-fridge-cool-a-room.mjs.
So what actually cools, and what doesn't
| Setup | Where the hot coil is | Net effect on the room |
|---|---|---|
| Fridge / freezer, door open | Inside: same room | +W · warms (a ~150 W space heater) |
| Window / split AC | Outside the window | −COP·W · cools (the whole point) |
| Dual-hose portable AC | Outside (both hoses vent + intake) | ≈ −COP·W · cools well |
| Single-hose portable AC | Outside (one hose), but the room leaks | cools, partially self-defeating |
The single-hose portable is the honest middle case. It does vent its hot coil outdoors, so it genuinely cools, but pushing one hose of air out the window leaves the room at slightly lower pressure, which sucks warm (often humid) outside air back in through every gap. It partially undoes its own work: still net cooling, just less than its label claims, and less than a dual-hose unit that both draws and dumps outside air. It never crosses over into heating the room the way an open fridge does; the difference is that its Qh still leaves.
The honest edges: where the fear is right, and what's idealised
The fear is partly right: locally and briefly. Stand in the cold-coil draft and you personally feel cooler: cold air is blowing on you, and for the first minutes the room hasn't warmed yet. The frame only flips on the whole room, time-averaged. There, the answer is not "cools a bit but heats more"; it is that the whole-room, time-averaged temperature always rises. There is no operating point where an open fridge nets cooling for the room.
Exactly true, not idealised. The net heat a door-open fridge adds to a sealed room equals the compressor's electrical power W, and this is independent of the COP. It follows from energy conservation alone (Qh = Qc + W): no efficiency assumption, no approximation. A more efficient fridge does not heat the room less.
Real fridges cycle. With the door shut a fridge runs its compressor only ~⅓–½ of the time (duty cycle), so its average draw is well below the running wattage. Prop the door open and it can't reach setpoint, so it runs near-continuously, which is why the "continuous W" figure here is the honest one for the open-door case, and why an open fridge also wears itself out.
The running number. ~100–250 W is a typical household unit's running compressor draw; large, old, or side-by-side units run higher (up to ~400–800 W), and the momentary start-up surge is higher still. We let you drag it because the conclusion (net = W) holds at every value.
Where COP comes from. COP = Qc/W is the heat moved per watt of work; a real fridge's is roughly 1.5–3, a good AC's 3–4. It is bounded above by the Carnot limit set by the two coil temperatures. It changes how much heat gets shuttled, never the leftover W when both coils share a room.