Records reviewed Sept. 3, 2026

2026 thermal briefRSS
DataCenterChill
Search records/Find suppliers

Cooling technology • Technology

Rear-door heat exchangers

A water-cooled coil takes the place of the rack's back door and cools the hot air on its way out.

RDHxretrofitrackliquid loop

Direct answer

What this record says

Rear-door heat exchangers is an established cooling architecture using building water, or a separate water loop. It is typically applied at Commonly applied to 30–100+ kW racks. Last reviewed Aug. 9, 2026 against 1 source.

1 sourceReviewed Aug. 9, 2026
Maturity
Established
Coolant
Building water, or a separate water loop
Typical density
Commonly applied to 30–100+ kW racks
Suppliers tracked
4 suppliers
MaturityEstablished
Cooling mediumBuilding water, or a separate water loop
Typical applicationCommonly applied to 30–100+ kW racks

Architecture

How heat moves

A rear-door heat exchanger (RDHx) places a water-cooled coil directly behind an air-cooled rack. Server fans push hot exhaust through a passive door, or door fans assist the flow in an active design. Heat crosses the coil into a water loop and then moves through pumps, heat exchangers, and the site's heat-rejection plant.

It fits retrofits and mixed halls without changing server internals. It cuts room heat but retains server-fan power and adds water, weight, depth, and service at each rack. The facility must provide water within the door's temperature, flow, pressure, and chemistry limits.

It also needs hose routes, leak detection, controls, door-swing clearance, floor capacity, and room-air management for any heat not captured. Water below room dew point can cause condensation. Published kilowatt ratings depend on entering air and water, flow, fan state, altitude, coil cleanliness, and server airflow.

Ask whether quoted capacity is room neutral and what remains after a door fan, pump, or water supply fails. Confirm rack fit, hinge side, cable access, quick-disconnect location, pressure drop, sound, power, monitoring, and service while servers run. Compare passive and active doors at the same duty conditions and include both door and server-fan energy.

01Components
02server air
03coil in the rear door
04building water

Why teams choose it

  • Works with ordinary air-cooled servers, with no changes inside them
  • Can be added one rack at a time
  • Catches the heat at the rack, so the room has less to remove

What to validate

  • Rack weight, door clearance, hoses, and aisle access all need planning
  • The servers' own fans still draw power
  • If the supply water is too cold, the coil will condense water in the room

Connected records

Companies in this category

View all companies in this category
Company

Motivair

A liquid cooling specialist for supercomputing sites, supplying both the rack equipment and the chillers behind it.

Buffalo, New York, United States
Company

nVent

Comes from electrical enclosures, and now supplies the racks, rear doors, and liquid plumbing that go with them.

London, United Kingdom
Company

STULZ

A precision cooling manufacturer that covers both the room air systems and the newer liquid equipment.

Hamburg, Germany
Company

Rittal

An enclosure manufacturer selling racks together with the cooling packages that bolt onto them.

Herborn, Germany

Connected records

Required equipment

View all required equipment
Equipment category

Rear-door heat exchangers

A water-cooled coil built into the back door of a rack, cooling the hot air as it leaves.

4 tracked suppliers
Equipment category

Cooling pumps

Pumps keep coolant moving; loss of flow can quickly force dense computing equipment to reduce power or shut down.

3 tracked suppliers
Equipment category

Heat exchangers

The component that passes heat from one loop of fluid to another without the two ever touching.

5 tracked suppliers

Evidence ledger

Sources and evidence

The links below show where the factual claims came from. Supplier specifications remain supplier-reported unless the record names independent operating evidence.

  1. 01
Record information
Record ID
DCC / TECH / REAR-DOOR-HE
Record reviewed
Aug. 9, 2026
Record first published
Aug. 9, 2026
External sources
1
Search visibility
Offered to search engines

Latest coverage

Intelligence mentioning Rear-door heat exchangers

View all intelligence mentioning rear-door heat exchangers
Intelligence item

Google's Brazos cools a liquid rack without plumbing the building

A sidecar rack takes heat from a liquid-cooled rack next to it and dumps it into the hot aisle, so an existing air-cooled hall needs no new pipework.

Jun 16, 2026 · Product
Intelligence item

Schneider Electric completes controlling investment in Motivair

Schneider acquired 75% of Motivair, adding specialist liquid-cooling capability to its data-center platform.

Feb 28, 2025 · M&A

Decision support

Guides and comparisons mentioning Rear-door heat exchangers

Vendor landscape

Rear-door heat exchanger suppliers

Rear-door units come almost entirely from infrastructure vendors that also supply racks, plant, and field service.

Aug 9, 2026 · 10 min

Direct answers

Frequently asked questions

Direct answers drawn from the record, its comparison fields, and the evidence linked below.

What is Rear-door heat exchangers?

A rear-door heat exchanger (RDHx) places a water-cooled coil directly behind an air-cooled rack. Server fans push hot exhaust through a passive door, or door fans assist the flow in an active design. Heat crosses the coil into a water loop and then moves through pumps, heat exchangers, and the site's heat-rejection plant. It fits retrofits and mixed halls without changing server internals. It cuts room heat but retains server-fan power and adds water, weight, depth, and service at each rack. The facility must provide water within the door's temperature, flow, pressure, and chemistry limits. It also needs hose routes, leak detection, controls, door-swing clearance, floor capacity, and room-air management for any heat not captured. Water below room dew point can cause condensation. Published kilowatt ratings depend on entering air and water, flow, fan state, altitude, coil cleanliness, and server airflow. Ask whether quoted capacity is room neutral and what remains after a door fan, pump, or water supply fails. Confirm rack fit, hinge side, cable access, quick-disconnect location, pressure drop, sound, power, monitoring, and service while servers run. Compare passive and active doors at the same duty conditions and include both door and server-fan energy.

Where is Rear-door heat exchangers typically used?

Commonly applied to 30–100+ kW racks. We class the approach itself as established.

What are the main advantages of Rear-door heat exchangers?

Works with ordinary air-cooled servers, with no changes inside them. Can be added one rack at a time. Catches the heat at the rack, so the room has less to remove.