A PC enthusiast has built an automated liquid-cooling system that routes coolant through a radiator mounted outside their house, using freezing winter temperatures to cool an Intel Core Ultra processor and NVIDIA GeForce RTX 4070 Ti Super. The custom setup reportedly keeps the GPU as low as 34°C and the CPU between 45°C and 50°C during gaming, while transferring much of the PC’s waste heat outdoors.
The builder, Reddit user Motor_Attention1865, documented the project in a post on r/pcmasterrace, explaining that the system took approximately two months to complete. The original motivation was straightforward: the gaming PC generated enough heat to make the room uncomfortable, even when outdoor temperatures were around -4°C.
Rather than repeatedly opening a window, the enthusiast developed a cooling system that automatically sends coolant through an external radiator when additional cooling is needed. An Arduino Mega controller, temperature sensors and a motorized valve regulate the process while attempting to prevent condensation inside the computer.
The PC itself features an Intel Core Ultra 7 270K Plus processor, an ASUS TUF RTX 4070 Ti Super and 48GB of DDR5-8400 memory. The processor has been delidded and fitted with a Thermal Grizzly direct-die water block, while the graphics card and memory also use custom liquid-cooling components.
The graphics card has undergone additional modifications, including a shunt modification that allows significantly higher power consumption than its original configuration. The builder claims the GPU can draw more than 500W under certain overclocked settings.
The internal cooling loop includes a 120mm rear radiator, a 360mm front radiator and an EK Kinetic D5 pump-reservoir combination. These components provide conventional liquid cooling independently of the outdoor system.
The external cooling setup adds an Alphacool XE240 240mm radiator equipped with two Noctua iPPC-3000 fans. Coolant travels through tubing passing through the house wall, driven by a second D5 pump housed in a separate enclosure beside the PC.
A motorized three-way valve determines how much coolant passes through the outdoor radiator and how much bypasses it. This allows the system to benefit from cold outdoor air without continuously exposing the PC’s cooling loop to extremely low temperatures.
The automated temperature management is the most distinctive part of the project.
The Arduino Mega monitors three coolant temperature probes and three temperature and humidity sensors, including two sensors inside the PC case and another measuring room conditions. A Python script running on the computer communicates with the controller and integrates with hardware-monitoring and fan-control software.
During normal operation, the system targets a coolant temperature approximately 10°C above the calculated dew point. For benchmarking, the builder can reduce that safety margin to 5°C.
The dew point is the temperature at which moisture in the surrounding air begins condensing on sufficiently cold surfaces. Allowing coolant tubes or water blocks inside a computer to fall below that threshold can cause moisture to accumulate around sensitive electronic components.
By monitoring temperature and humidity, the controller adjusts the valve and external radiator fans to maintain the desired coolant temperature. The builder also implemented a fallback mechanism that shuts off the outdoor cooling section if communication fails or the controller detects an abnormal condition.
Freezing temperatures introduce another challenge. The enthusiast added ethylene glycol to Aquacomputer Double Protect Ultra coolant, reporting that the mixture’s freezing point dropped from approximately -18°C to -28°C.
However, antifreeze additives introduce their own compatibility considerations. In a discussion following the original post, the builder expressed concern that the increased glycol concentration could eventually affect the acrylic GPU water block.
The reported cooling results demonstrate what the system can achieve under favorable winter conditions.
During Unigine Heaven testing, the RTX 4070 Ti Super reportedly maintained a GPU temperature of approximately 37°C, with hotspot temperatures in the mid-40s. Coolant entering the PC was held at 15°C, while the outdoor radiator fans operated at roughly 35% speed.
After an hour of Counter-Strike 2, the builder recorded a GPU temperature of 34°C and CPU temperatures between 45°C and 50°C.
More demanding synthetic benchmarks produced higher readings. Cinebench R23 pushed the processor to 52°C, while 3DMark Steel Nomad produced a GPU temperature of 48°C.
These figures are the builder’s own reported measurements rather than independently verified benchmark results. The processor’s delidding, extensive water-cooling hardware and graphics card modifications also contribute to the temperatures, making it difficult to isolate the outdoor radiator’s precise improvement.
The enthusiast reported that delidding alone reduced CPU temperatures from approximately 85–90°C to 60–65°C under conventional ambient cooling, with the external system bringing them down to around 40–45°C under the builder’s described conditions.
The project illustrates a different approach to extreme PC cooling compared with an RTX 3080 cooling experiment using a repurposed air-conditioner radiator, which achieved a reported GPU temperature of 28°C. Both systems explore unconventional ways to dissipate heat, although the new build adds automated coolant routing and dew-point monitoring.
There are practical limitations. The outdoor setup requires plumbing through a wall, additional pumps, custom electronics, suitable coolant and protection against freezing and condensation. Its effectiveness also depends heavily on outdoor temperatures, making the arrangement less useful during warmer weather.
The builder acknowledged that the external radiator installation was initially a proof of concept and may need changes for summer operation. The project also experienced several development problems, including an electrical fault, a missing check valve and a coolant spill during initial filling.
Despite the complexity, the system has achieved its intended purpose according to the builder: reducing unwanted room heating while maintaining low component temperatures during gaming.
The project remains an enthusiast modification rather than a practical alternative to conventional cooling for most gaming PCs, but it demonstrates how automated thermal management can make use of outdoor temperatures without exposing internal components directly to sub-zero coolant.
