Air, completely.

Every component is cooled, not only processors.

Servers have no fans of their own.

The hall needs no air handling for IT load.

Cold plates still leave a residual air duty.

Immersion is the only approach that does not.

Simplicity against heat flux.

Single-phase keeps the fluid liquid and pumps it.

Fluids are cheaper and easier to handle.

Two-phase boils and condenses to move heat.

It reaches far higher flux with little pumping.

It also carries higher fluid cost and tighter rules.

Lifting a wet server out and letting it drain.

That is a different operational model entirely.

Staff need training before the first tank.

The room needs drip and drain provision.

Lifting equipment is needed above a certain size.

Plan the procedure before deployment, not after.

More than most people expect.

Some polymers, adhesives and labels are affected.

Thermal interface materials can degrade.

Optical transceivers are a known sensitivity.

Check component by component, not by assumption.

The vendor's approved list is the constraint.

Density and useful heat.

Rack powers air cannot approach become possible.

Fan energy disappears from the servers.

Hall air handling largely disappears too.

Return heat is warm enough to reuse.

That makes heat recovery genuinely practical.

Enough to matter commercially.

Volume scales with tank size, not IT load.

Two-phase fluids cost considerably more per litre.

Losses through evaporation and service add up.

Ask for expected annual make-up.

Budget it as a recurring line.

Sometimes, with modification.

Fans are removed and thermal materials replaced.

Warranty positions vary widely between vendors.

Some hardware is sold immersion-ready.

Confirm the warranty before submerging anything.

Trial with a small tank before committing.