Aisle Separation
Aisle separation means the asics take air from one side and blow it out into a separate volume, from which it leaves the building.
What aisle separation is
An air cooled ASIC works like a pump: it pulls cold air in on one side and blows hot air out on the other. All the power it draws turns into heat, so an asic at 3.5 kW is a 3.5 kW heater, with no discount.
If the air blown out comes back to the intake, recirculation starts. The intake temperature rises, chip temperatures follow, the asic drops frequencies and in the limit goes into protection. Hashrate falls, and the cause lies neither in the miner nor in the firmware.
Separation solves this physically. The cold side and the hot side live in different volumes with a partition between them, while the gaps between asics and the empty slots in the rack get closed with blanking panels. Air takes the only route left open to it: in from outside, through the asics and out.
On one or two asics a room with an intake opening and an extract opening on different walls is enough. From five asics up the lack of separation starts showing in the temperatures, and past that point you cannot manage without it.
Quick reference table
| The point | keep hot air from coming back to the intake |
| Heat from an asic | equals its draw, 3.5 kW means 3.5 kW of heat |
| Sign of recirculation | intake and chip temperatures climb |
| What closes the gaps | a partition and blanking panels in the rack |
| From what scale it is needed | noticeable from five asics up |
How to do it
Put the intake and the extract on different walls and at different heights: cold air comes in low and hot air leaves high.
Set the asics in one row the same way round, intake facing intake. A single asic turned across ruins the whole row.
Close the gaps. An empty slot in the rack is a short path for hot air back to the intake, and a blanking panel here does more than an extra fan.
Measure the temperature at the intake rather than in the room. The difference between those two figures is your recirculation.
An example on live asics
Four asics stand in a room with the intake and the extract side by side in one wall. The intake temperature climbs through the first hour, the chips go up, and hashrate sags by evening. The extract gets moved to the opposite wall, a partition goes in between the row and the intake, and temperatures come back to the figures of the first minutes.
Related terms
Where to go next on the site
Hardware
- ASIC Miner knowledge base
- Antminer S21 tool
Numbers
Questions and answers
Is a powerful extract fan enough on its own
No, not while hot air sits next to the intake. With recirculation a powerful extract drives the same warmed air around in a circle.
Is separation needed on two asics
Usually not; a room with intake and extract on different walls will do. The problem starts with scale.
Does air conditioning help
It helps, but it adds from a quarter to a third of the heat it removes to your bill. Killing the recirculation first comes cheaper.
How the terms connect
Every link in the chain is clickable. Orange marks where you are now.
Looking for an ASIC miner
The catalog holds 212 models. You can compare them by hashrate and by joules per terahash, then plug your own rate into the calculator and see what stays in your pocket.
Page written and checked by Denys Klimchuk. Updated .