Best case for a two-GPU local-LLM box

Two big GPUs can turn a roomy-looking tower into a very expensive sandwich. Start with the motherboard’s slot spacing, then buy a case that leaves space below the lower card and beside the power plugs.

Choose the Phanteks Enthoo Pro II Server Edition for the most rear-slot room, Corsair 7000D Airflow for a mesh-front build with included fans, or Fractal Define 7 XL for a closed-panel tower. All three have at least eight horizontal expansion slots. Your board still decides where the cards sit.

Specs and drawings from the makers, checked October 25, 2026; slot-spacing examples are calculated.

The three-case shortlist

Case / pick	Key specifications
Enthoo Pro II Server Edition — PH-ES620PC_BK02, closed panel. Pick for maximum rear-slot room.	11 horizontal slots; ATX, E-ATX and SSI-EEB, up to a 375 × 330 mm board. Maker GPU-length limit: 503 mm. Front: 4 × 120 or 3 × 140 mm fans; left bracket: 3 × 120 mm. No bottom fan position listed in the Server Edition manual. PSU maximum length and cable-space dimension are not specified there.
7000D Airflow — CC-9011218-WW, black. Pick for a mesh-front build with included fans.	8 horizontal + 3 vertical slots; ATX and E-ATX up to 305 × 277 mm. Current maker GPU-length limit: 450 mm; ATX PSU: 225 mm. Front: 4 × 120 or 3 × 140 mm; side: 4 × 120 mm. Three 140 mm AirGuide fans included. No bottom fan position listed.
Define 7 XL Solid — FD-C-DEF7X-01, black. Pick for closed steel panels and nine horizontal slots.	9 horizontal + 3 vertical slots; ATX, E-ATX and SSI-EEB. GPU length: 505 mm in open layout with a front fan, 530 mm without; 340 mm in storage layout. ATX PSU: 250 mm with both HDD cages installed. Front: 4 × 120 or 3 × 140 mm; bottom: 2 × 120/140 mm. Three 140 mm GP-14 fans included; 30 mm cable-routing space behind the motherboard.

Sources: Phanteks Server Edition specifications and manual; Corsair’s current specifications and fan/mounting guide; Fractal’s exact solid-panel model and current V3 manual.

Buy the slot spacing before the case

Count the rear bracket positions from the top, starting at one, and map your motherboard’s connectors onto them. These positions are different from connector names such as PCIEX16_1. A full-length connector can also have fewer electrical lanes; read the board manual’s lane-sharing table separately.

For two equally thick cards, the nominal gap is the distance between their starting positions minus one card’s thickness. Here is the arithmetic for illustrative board layouts:

Upper / lower starting position	Each card	Gap between cards	Rear slots needed
2 / 4	2.5 slots	Overlap by 0.5 slot	Reject this layout
2 / 5	2.5 slots	0.5 slot	7
2 / 6	2.5 slots	1.5 slots	8
2 / 6	3 slots	1 slot	8
2 / 7	3 slots	2 slots	9

These are nominal slot-envelope calculations, not thermal results. Use the cards’ actual millimetre dimensions—including backplates and cooler overhang—for the assembly.

The last row explains why the ninth horizontal slot can be useful: a three-slot lower card beginning at position seven extends through position nine. An eight-slot rear panel runs out of room. Conversely, adding an eleventh case slot cannot move two closely spaced motherboard connectors apart.

For the recorded B450 configuration and workload results, see our two-GPU Ollama build. Choose your own board layout from its drawing rather than treating that configuration as a physical template for larger cards.

Phanteks Server Edition: the most room below the board

Pick the Enthoo Pro II Server Edition when rear-slot space is your first constraint. Its eleven horizontal positions give a lower cooler more room to extend beneath the board’s last connector. The exact BK02 Server Edition matters: the ordinary Enthoo Pro II has a different rear layout.

The Server Edition manual shows the movable three-fan left bracket. You can reposition it toward the front, but that arrangement blocks the right-side fan and HDD positions. Decide which layout you want before filling the tower with drives.

Plan front intake and top/rear exhaust, then decide whether the bracket helps your particular card arrangement. Allocate your fan shopping separately; fan mounting capacity is what the specifications describe. For the PSU, measure its body and the space needed to plug in and route cables against the chassis drawing.

Corsair 7000D Airflow: included fans, eight horizontal slots

Choose the 7000D Airflow when your board/card layout fits eight rear positions and you want three included 140 mm fans to get started. Its published 450 mm card-length limit and 225 mm PSU limit cover different dimensions: a short-enough power supply still needs room for its connectors and cable bends.

The mounting guide provides front, roof, rear and motherboard-tray fan positions. Using the side fan mounts requires removing the cable cover. Route the power leads before the cards make that area awkward to reach.

Wide workstation boards need particular attention: Corsair’s E-ATX envelope is 305 × 277 mm. Match the board dimensions, not just the E-ATX badge.

Define 7 XL: closed panels and a choice of layouts

Choose the Define 7 XL Black Solid if you want sound-damped steel panels, nine horizontal slots and a tower that can also hold a substantial drive collection. Fractal supplies both solid and ventilated top-panel options. Choose the ventilation layout around the heat your cards produce; use our quiet-cooling guide for fans and control advice.

For long cards, use the open layout. The GPU clearance drawing, printed page 51 shows why: storage layout cuts length to 340 mm and GPU width to 150 mm. That width is the dimension toward the side panel, distinct from cooler thickness across expansion slots.

Bottom fans share a busy area with the lower GPU, shroud and drive cages. Put those components on the same drawing before buying extra fans. A large tower makes the planning easier; it doesn’t remove the conflicts.

Will your two cards fit? Use this checklist

• Board spacing and lanes: mark both starting positions, cooler thicknesses and the gap. Read which connectors remain usable with your SSDs or other cards installed.
• Length: subtract any front radiator, fan or drive arrangement that intrudes into the selected GPU space. Use the clearance for your chosen case layout.
• Height and power plugs: measure from the card to the side panel with its power connector and the cable maker’s required bend allowance. CPU-cooler height is a separate specification.
• Lower-card intake: locate the PSU, shroud, bottom fans, headers and support brackets beneath the cooler. Keep cables out of fan blades and intake openings.
• PSU wiring: allocate the necessary sockets and separate cable runs using our two-GPU PSU guide. Reach matters as well as wattage. Leave room to unplug and reseat each connector during maintenance.

Make a small parts worksheet before ordering: exact GPU model, length, width toward the side panel, thickness, power connectors and intended rear position. Add the motherboard model and the slots enabled with your planned SSD configuration. Put both cards on the same sketch, including any anti-sag support. It is much easier to move a rectangle on paper than discover that the lower card covers a header you still need to connect.

Vertical mounting is a separate layout choice. Corsair lists three vertical positions and a separately purchased riser; Fractal’s product sheet likewise lists a separate vertical riser. For a straightforward two-card build, start with horizontal mounting: it keeps both board connectors directly accessible. A riser arrangement needs its own check for card-to-card and side-panel clearance.

If your mini PC has no suitable internal slots, jump to the OCuLink and USB4 eGPU guide. If you’re still choosing cards, use the GPU buying guide and local-LLM hardware guide.

Build in the order that saves your knuckles

1. Open the case, choose its storage/fan layout, and remove the panels and brackets needed for access.
2. Install the board and dry-fit both cards to check the full envelope. Remove the cards again while you work on wiring.
3. Install the PSU, connect its modular leads, and route CPU, GPU and front-panel cables. Fit fans or radiators that the cards would obstruct.
4. Refit the cards in the order that leaves their latches and screws reachable. Add supports without blocking either cooler.
5. Connect GPU power fully, secure loose wiring, and close the side panel without pushing against a connector.
6. Boot, verify that both GPUs are detected, then run your intended model while watching temperatures and fan behaviour. Tune from that result.

The final pick: Phanteks Server Edition for maximum horizontal-slot room; Corsair 7000D Airflow for an eight-slot build with included fans; Define 7 XL for nine slots and closed steel panels. The winning case is the one that fits your board, both coolers and the cables—with space left to work.