RentServers.comBy the RentServers.com team · Updated
kW per rack, by system
Maximum system power from the vendors' published specifications, multiplied out per rack. Real draw under load is usually 70 to 90% of maximum, but contracts and circuits are sized to the maximum.
| System | 1 per rack | 2 per rack | 3 per rack | 4 per rack |
|---|---|---|---|---|
| 8x H100 SXM (HGX)10.2 kW each | 10.2 kWAir | 20.4 kWAir with containment or rear door | 30.6 kWAir with containment or rear door | 40.8 kWRear door or direct-to-chip liquid |
| 8x H200 SXM (HGX)10.2 kW each | 10.2 kWAir | 20.4 kWAir with containment or rear door | 30.6 kWAir with containment or rear door | 40.8 kWRear door or direct-to-chip liquid |
| 8x B200 (HGX)14.3 kW each | 14.3 kWAir | 28.6 kWAir with containment or rear door | 42.9 kWRear door or direct-to-chip liquid | 57.2 kWRear door or direct-to-chip liquid |
| 8x B300 (HGX)14 kW each | 14.0 kWAir | 28.0 kWAir with containment or rear door | 42.0 kWRear door or direct-to-chip liquid | 56.0 kWRear door or direct-to-chip liquid |
| 8x MI300X (OAM)10 kW each | 10.0 kWAir | 20.0 kWAir | 30.0 kWAir with containment or rear door | 40.0 kWAir with containment or rear door |
Maximum system power from the vendors' published specifications (MI300X: estimate, 8 x 750 W GPUs plus host). Cooling bands are rules of thumb; each facility commits its own kW per rack.
For comparison, a typical enterprise cabinet of a few years ago drew 5 to 10 kW. A rack-scale system such as GB200 NVL72 is in the 120 kW class and is liquid-cooled by design.
Where air cooling stops
- Up to about 15 to 20 kW per rack: conventional raised floor or slab with hot and cold aisle containment.
- About 20 to 40 kW: containment plus higher airflow, in-row coolers or rear-door heat exchangers.
- About 40 to 75 kW: active rear-door heat exchangers, or direct-to-chip liquid cooling for the GPUs with air for the rest.
- Above about 75 kW: direct-to-chip liquid cooling with a coolant distribution unit, or immersion.
These bands are rules of thumb, not guarantees. Hot climates, high altitude and the facility's design temperature all move them. Ask each facility for the kW per rack it will commit to in writing for your exact cooling method.
Liquid cooling options
- Rear-door heat exchangers. A water-cooled coil on the back of the rack removes heat from exhaust air. Servers stay standard air-cooled models.
- Direct-to-chip. Cold plates on GPUs and CPUs, fed by a coolant distribution unit (CDU) on a secondary loop. Typically removes most of the heat through liquid; the remainder still goes to air.
- Immersion. Servers sit in dielectric fluid. Very dense, but it needs compatible hardware and changes how you service it.
Questions to ask: who owns the CDU, the supply water temperature and flow per rack, leak detection and shutoff, water treatment, and who is liable if a leak damages your servers.
Sizing circuits
US electrical code limits continuous loads to 80% of a breaker's rating. Usable power per circuit is volts x amps x 1.732 (for three-phase) x 0.8:
| Circuit | Usable continuous power |
|---|---|
| 208 V three-phase, 30 A | 8.6 kW |
| 208 V three-phase, 60 A | 17.3 kW |
| 415 V three-phase, 30 A | 17.3 kW |
| 415 V three-phase, 60 A | 34.5 kW |
| 415 V three-phase, 100 A | 57.5 kW |
With A+B redundant feeds, each feed must carry the whole rack on its own, so a 40 kW rack needs two feeds that can each deliver 40 kW. Breakered billing charges for the circuit size whether you use it or not; metered billing charges for what you draw, plus the facility's power usage effectiveness (PUE) multiplier.
Checklist before you sign
- Committed kW per rack and per row, in writing, for your cooling method.
- Circuit voltage, amperage, phase and redundancy.
- Billing model: all-in, breakered or metered, and the billed PUE.
- Cooling: method, design temperature and who maintains it.
- Delivery date for energized power, and credits if it slips.
- Floor loading: a full GPU rack can weigh well over 1,000 kg.
Questions
How many H100 servers fit in a rack?
By power, usually two to four. Each 8-GPU H100 server is rated at about 10.2 kW maximum, so four need about 41 kW, which most halls can only cool with rear-door or liquid assistance.
Do B200 and B300 servers need liquid cooling?
Air-cooled 8-GPU versions exist, at about 14 kW per server. One or two per rack can be air-cooled in many halls; denser racks generally need rear-door heat exchangers or direct-to-chip liquid cooling.
What is the difference between breakered and metered power?
Breakered power bills for the circuit's size regardless of use. Metered power bills for the energy you actually draw, multiplied by the facility's billed PUE. High, steady GPU loads often favor metered power.