What the build does
The modder's room has heated floors, and the PC was dumping too much heat under his table even in 25 °F (-4 °C) weather. Instead of opening a window by hand, he built what amounts to a split system, much like a mini-split air conditioner with an indoor and an outdoor unit. Mezha's coverage uses the same comparison: much like an air conditioner, the PC has both indoor and outdoor units. GameGPU says the project took two months to develop.
The PC itself is a serious machine:
- CPU: a delidded Core Ultra 7 270K Plus with a Thermal Grizzly 1851 Mycro Pro direct-die block and Conductonaut Extreme liquid metal.
- GPU: an RTX 4070 Ti Super with a Bykski water block.
- Memory: 2x24GB G.Skill DDR5-8400, water-cooled with Bykski heat spreaders and an IceManCooler two-channel block.
- Internal loop: a 120mm rear radiator, a 360mm front radiator and an EK Kinetic D5 pump-reservoir. Techtroduce notes that these components provide conventional liquid cooling independently of the outdoor system.
The outdoor section is a 240mm radiator with two Noctua iPPC-3000 fans. GameGPU identifies it as an Alphacool XE240 unit. A box next to the PC holds a Bykski D5 pump and reservoir that pushes water outside, but the external radiator isn't used until the PC needs extra cooling.
How the control system works
The clever part is the control logic. A Python script launches when the PC starts, connects to the Arduino, takes over its built-in automatic control mode, and interfaces with HWi and FanControl. The Arduino Mega reads three coolant probes plus three temperature and humidity sensors. Two of the sensors are in the case and one is in the room. Based on those readings, it decides where to point the motorized three-way valve.
Techtroduce describes the valve's job this way: it determines how much coolant passes through the outdoor radiator and how much bypasses it. That means the PC is never exposed to raw outdoor-temperature coolant. The loop is mixed to a target.
The real enemy is condensation
Anyone who has run a chilled loop knows the rule. If coolant gets below the dew point of the environment, condensation forms, potentially shorting out PC components. The Arduino therefore calculates the dew point from the temperature and humidity readings. Tom's Hardware reports that the builder set the Arduino to close off the outside radiator at +10 °C above the dew point, or +5 °C during benchmarking.
The builder's own example, as relayed in the Reddit discussion, shows how this works. With a 6.5 °C dew point, the valve blends cold coolant into the return until the loop reaches 11.5 °C. He says the blending happens outside the PC, and that the line returning to the PC is watched by a separate NTC sensor. The aim is that no tube entering the case sits below the dew point.
He also says the system defaults to passive operation. A lost connection or an abnormal condition is meant to shut off the outdoor section. These are the builder's descriptions of his own design. Nobody has independently validated the fail-safe behavior.
This approach matches what hobbyists have long recommended. An Overclock.net poster once suggested that a thermostatic three-way valve could blend radiator supply water with recirculated computer loop water, with the probe on the supply line to the computer. The same thread also pointed to an Arduino with a humidity sensor for a dynamic setpoint that follows ambient dew point. This build is a polished version of that idea.
Freezing protection
Outdoor tubing in sub-zero weather brings a second risk: ice. The builder added pure ethylene glycol to Aquacomputer Double Protect Ultra Clear coolant. Tom's Hardware says this lowers its freezing point from -18 °C to -28 °C, as reported by the modder. That is a reported property of his specific mixture, not a tested result or a recommended recipe.
The reported numbers
The temperatures below are the builder's own, relayed by Tom's Hardware and other outlets:
| Scenario | Reported temperature |
|---|---|
| CPU while gaming | about 45-50 °C |
| GPU while gaming (Tom's Hardware) | about 37 °C |
| Cinebench R23, CPU | 52 °C |
| 3DMark Steel Nomad, GPU | 48 °C |
Other coverage cites a slightly lower gaming GPU figure of 34 °C, from an hour of Counter-Strike 2. That is a different workload from the 37 °C figure. Techtroduce also reports that coolant entering the PC was held at 15 °C while the outdoor fans ran at roughly 35%.
What these numbers don't prove
Be careful with the headline. Techtroduce makes a fair point: the delidding, the extensive water-cooling hardware and the GPU modifications also contribute, making it hard to isolate the outdoor radiator's improvement. By the builder's account, the CPU ran at 85-90 °C before delidding. It fell to 60-65 °C afterward on ambient cooling, then to 40-45 °C with the external system on. That is a useful progression, but it is one user's report on one heavily modified system. No controlled comparison exists.
Other caveats:
- Seasonal limits. The builder calls it a proof of concept. He says the exterior mounting may need rework for summer, when outdoor air is no longer a bargain.
- Not a how-to. The thresholds, sensor placement and valve logic come from one person's experiment. They are not validated instructions, and a mistake here puts liquid next to expensive silicon.
- Simpler alternatives. A commenter suggested two separate loops joined by a heat exchanger, which would keep outdoor coolant physically away from the PC. The builder replied that the single-loop design emerged during construction and he stuck with it. That alternative is untested.
- Construction troubles. The builder mentions a missing check valve, a power-board fault that left the outside pump running, a broken solder joint mistaken for a software bug, and a spill while filling the exterior loop.
Why it matters to PC builders
Most enthusiasts chase lower temperatures. This build is aimed at where the heat ends up. A 600-800 W gaming system, the figure the builder gives, is a space heater with a graphics card. In a heated-floor room, that is wasted energy. Pushing it outdoors is conceptually the same trick as a mini-split, only with an Arduino instead of an HVAC contractor.
The control problem is the part worth studying. Cold coolant is easy to get. Cold coolant that stays safely above the dew point as humidity changes is the hard part. Sensor redundancy, a fail-passive default and a margin that tightens only for benchmarking are sensible habits for anyone building custom loops, even if you would never mount a radiator on your wall.
Would most people do this? No. Is it a neat reminder that a PC's waste heat is an engineering resource? Absolutely. It also saves the builder from opening a window.