Blog · Hardware Building · September 20, 2026 · 7 min read

PSUs, Cooling, and 24/7 Inference: Building a PC That Can Run AI All Day

Gaming stresses a PC in short bursts; local AI holds the GPU at 100% power draw for hours. A machine that plays games all weekend without complaint can still throttle, whine, or trip its power supply during an overnight batch of inference. Here is how to build (or upgrade) for sustained loads.

Power supply: size for the peak, quality for the marathon

• Add it up: GPU TDP + CPU TDP + ~100 W for the rest, then multiply by roughly 1.4–1.5 for transient spikes. A 450 W GPU plus a 150 W CPU wants an 850–1000 W unit — a 575 W GPU (RTX 5090 class) wants 1200 W.
• Do not cheap out on the tier. A quality 80+ Gold unit from a reputable brand survives years of sustained load; bargain PSUs drift, whine, and die under exactly this duty cycle.
• Multi-GPU math is linear. Two 350 W cards plus the system means planning for 900+ W of real draw — see our dual-GPU guide.

Cooling: sustained load changes the rules

• Airflow beats RGB. Inference is a steady thermal wall: front-to-back case airflow with more intake than exhaust keeps VRAM and power stages — not just the GPU core — under control. Memory chips running hot cause errors and throttling before the core does.
• Watch the memory junction temperature. Monitoring tools expose it; if long sessions push past the high-80s (Celsius), improve case airflow or set a saner power limit — a slightly slower but cool and stable card outperforms a throttling one.
• Dust is a scheduled task. A 24/7 inference box filters nothing; clean intakes monthly. Clogged filters quietly turn a quiet build into a furnace.

Noise and placement

Under sustained load, fans sit at high RPM for hours. If the machine shares your room, prefer larger, slower-spinning case fans, set a sensible custom fan curve, and consider placing the rig where the hum does not matter. Some builders deliberately run slightly lower power limits — trading 5–10% speed for a dramatically quieter, cooler machine.

The electricity connection

Remember that TDP is a running cost, not just a cooling spec: a 450 W card at 200 hours a month adds roughly $13.50 at $0.15/kWh. Our Hardware panel shows TDP for every card, and the crossover chart turns it into a monthly bill you can compare against cloud pricing.

Build it once, keep it cool, and the same machine will chew through models around the clock for years — which is exactly the usage pattern where local inference shines.