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Antminer S21 Underclock

There is no real underclock table for the Antminer S21 — and pages showing exact settings for it are guessing. No usable extraction preset set exists for this model: the catalog rows shown for the air unit are value-identical to the S21 Hydro set, and cooling changes the sustainable envelope. This page explains what that means, the watt-target method that works without a published envelope, and what we can actually verify.

Antminer S21 — tuning envelope Unknown

No air-cooled S21 extraction set exists; the catalog rows under this slug are value-identical to the S21 Hydro set. Air cooling changes the sustainable envelope, so no air numbers are published (see the S21 Hydro record).

The honest way to tune this model today: set a watt target in your firmware and let the autotuner derive frequency and voltage for your unit. That method needs no published envelope — it is the whole point of autotuning firmware. Pages showing exact “underclock settings” for this model are publishing stock-spec numbers or another SKU's data; when a set for this unit clears source-integrity checks, its envelope will appear here with a status.

For what this chip generation does in the models we can verify, see the generation efficiency bands on the index — context only, never a claim about this SKU.

Set the target in your firmware

Circuit math vs. PSU reality: the 1,440 W / 1,920 W lines are the continuous-load limits of 120 V 15 A / 20 A circuits (80% of breaker rating, per NEC continuous-load practice). Wattage fit alone does not make a 120 V miner: stock Bitmain APW-series supplies of the S17/S19/S21 generations accept 200–240 V input only, so a 120 V build is a PSU-level project regardless of watt target.

Frequency and voltage are calculated at runtime by the firmware autotuner — never fixed presets; per-unit silicon quality, ambient temperature and cooling shift real results.

These envelopes are derived aggregates (bounds, bands, counts) — the row-level operating points, the interactive picker and the CSV/JSON of the source data live in the ASIC Power Profiles Database, the single source dataset for every number on this page.

Antminer S21 full specifications → · Family / firmware hub → · Row-level operating points (source dataset) → · All tuning envelopes →

Related products, repair, and setup paths

Last reviewed August 13, 2026.