Overview.
| What it is | A service enclosure beneath the M3 changing-room bench for quiet on-site computing hardware. Where M3 is unsuitable, equipment may sit in an adjacent or external technical compartment with its own reviewed heat path. |
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| What it does | Every computer turns electricity into computation and heat. M4 places that work where the heat has a planned use—approximately 1.1 kW of recovered warmth into the changing room and cabin structure before bathing. |
| What it does not | It does not replace the sauna stove, generate steam or löyly, or promise energy savings without measurement. |
System.
| Heat path | Warm air routes to the M3 changing room, a warmer M1 starting condition, or another reviewed thermal load. When heat is no longer useful, an automated bypass rejects it outdoors. |
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| Workload | The same thermal principle applies whether the equipment runs local AI inference, Bitcoin network computation, or another suitable workload. Hardware is assessed separately from the thermal result. |
| Separation | Compute equipment is not installed inside the M1 bathing cabin. M4 does not remotely start or control the sauna stove. |