What Is External Radiator Tubing Pass-Through? (Floor Box)
An external radiator tubing pass-through is a protected opening, often built into an accessible floor box, that lets coolant hoses connect a PC to a radiator in another area. It must protect the hoses from sharp edges and kinks, keep connections serviceable, and preserve any required floor fire rating. There is no universal code size for this opening.
The neatest route can create the most hidden risk: hoses disappear into the floor, but a leak or damaged line may also become harder to find. I plan a pass-through as a service point, not just a hole. The floor assembly, hose limits, fittings, and radiator location all affect the detail.
Here, “external radiator” means a PC liquid-cooling radiator connected by flexible coolant hoses. If you mean a hydronic heating radiator, do not use this guide as a plumbing design. Heating pipework has different materials, temperatures, pressures, and code requirements.
Plan the Route and Identify the Floor Assembly
Start by identifying what the floor is made of and what lies inside it. A pass-through that works in a non-rated floor may be unsuitable in a rated assembly. Before cutting, locate framing, wiring, plumbing, and the planned radiator and PC positions.
A floor box is an accessible enclosure or protected opening at floor level. It can organize the hose route, but an ordinary electrical floor box is not automatically approved for liquid hoses. Its listing may cover electrical devices only, and its internal edges may harm tubing.
Survey and record:
- Floor type, thickness, joist direction, and any required fire rating.
- Concealed utilities and the location of floor framing.
- Hose outside diameter, fitting size, and the manufacturer’s minimum bend radius.
- The radiator’s position, hose length, and access needed to inspect connections.
- Whether the floor box or sleeve is suitable for the hose and the actual floor assembly.
Do not drill or notch a joist, truss, or engineered floor member unless its member-specific limits have been checked and required approval obtained. If the route crosses a rated floor, identify the tested firestop detail before making an opening. When you cannot confirm the assembly or services, pause and ask a qualified trade or building official to review the plan.
Check Hose Bend Radius, Access, and Radiator Clearance
Bend radius is the smallest curve a hose can make without exceeding its maker’s limit. That limit depends on the hose, so there is no safe universal number to apply. A tight turn at the floor box can pinch a line, restrict flow, or put strain on a fitting.
Measure the route using the actual hose and fittings, not just the hole diameter. Include the fitting envelope, the space needed to turn the hose, and any movement when the PC or radiator is serviced. The hose must pass through without being forced, flattened, or dragged over an unprotected edge.
| Check | What to use | Why it matters |
|---|---|---|
| Hose opening | Hose outside diameter and fitting dimensions | A hose may fit while its fitting cannot pass or turn |
| Bend | Hose maker’s minimum bend radius | Avoids a sharp curve or crushed line |
| Edge protection | A compatible sleeve, grommet, or pass-through | Keeps tubing from rubbing on the opening |
| Service access | Reachable fittings and visible hose sections | Makes inspection and leak response practical |
| Fan space | Radiator and fan maker’s clearance guidance | Prevents the route from blocking intake or exhaust |
There is no code CFM value for this pass-through. CFM means airflow volume per minute, but the relevant airflow limits come from the radiator and fan manufacturers. Keep hoses and the box clear of the fan faces and preserve the equipment’s stated intake and exhaust space.
Plan for inspection as well as installation. Keep joints accessible, and do not bury a connection where a leak could go unseen. A floor box should allow a person to check the hose path and reach the fittings without removing finished flooring or damaging the firestop.
Install the Sleeve, Protection, and Required Firestop
A sleeve or purpose-made pass-through protects the hose where it crosses the floor. Choose one that fits the hose and its route, has safe contact surfaces, and can be installed in the floor assembly without unauthorized structural cuts. Confirm the product’s stated use; a generic grommet is not a substitute for a rated firestop.
Use this sequence:
- Mark the opening only after locating framing and concealed services. Recheck the hose route and fitting clearance.
- Cut and frame the opening only as allowed for that floor construction. Do not weaken structural members to make the box fit.
- Install the compatible sleeve or pass-through. Protect every hose-contact edge, including edges inside the box.
- Support the hoses independently so their weight and movement do not pull on fittings or rest on a sharp opening.
- Keep joints reachable for inspection. Route the hose without exceeding its maker’s bend limit.
- Where the floor is fire-rated, install the listed firestop system specified for the actual floor construction and penetrant.
A firestop system is a tested set of materials and installation details meant to maintain a barrier’s fire performance at a penetration. For a rated floor, use a system listed for that assembly and penetrant, tested to ASTM E814 or UL 1479. Generic expanding foam or caulk is not a substitute. Follow the listed system’s limits and instructions; if no applicable system is clear, seek approval before proceeding.
Also account for wiring. Keep the tubing route separate from electrical conductors where required, and protect wiring from physical damage under the locally adopted electrical code, such as applicable NEC provisions in the United States. An electrical floor box listing does not establish that the box is suitable for coolant hoses.
Verify Structural, Firestop, Airflow, and Leak Performance
Before closing the floor box or putting it into service, check the whole route. Look for crushed hose, sharp contact points, stressed fittings, blocked fan faces, and inaccessible joints. Confirm that any firestop is complete and matches its listed system, not merely that the opening looks sealed.
I use a simple dry-run approach: route the hoses, inspect the bends and clearances, and confirm that the PC and radiator can be moved or serviced as planned. Then run the cooling system according to its manufacturer’s instructions and check the connections for leaks before concealing any part of the route. Follow the equipment maker’s testing guidance; do not improvise a pressure test or exceed a component’s rating.
| Situation | Suitable next step | Avoid |
|---|---|---|
| Non-rated floor, accessible route | Use a compatible protected pass-through and inspectable hose path | Bare tubing against a cut floor edge |
| Rated floor assembly | Confirm an applicable listed firestop system for that floor and penetrant | Generic foam or an assumed seal |
| Hose bends near the box | Compare the installed curve with the hose maker’s bend limit | Forcing a tight turn to fit the opening |
| Electrical floor box already installed | Check the product listing and get approval for the proposed use | Assuming electrical approval covers liquid tubing |
| Joist or engineered member blocks the route | Reroute or obtain member-specific review and approval | Cutting or notching without verification |
Keep the as-built details: product names, hose type, firestop system information, and any approval. That record helps with later inspection, repairs, and changes to the equipment. If the installation cannot be inspected or its firestop cannot be verified, treat it as unfinished.
Example Layouts and Common Decisions
These examples show how the same goal changes with the floor and equipment. They are planning scenarios, not tested designs or code approvals. The actual opening, hose curve, and firestop depend on the product instructions and the specific floor construction.
In a non-rated floor with an accessible space below, a homeowner may place the box where the hose can rise smoothly to the PC and continue toward the radiator. The route still needs protected edges and reachable connections. A direct, serviceable path is often better than a shorter route that forces a tight turn.
In a rated floor, the first decision is the applicable firestop system, not the box size. If the chosen system does not cover the floor type and penetrant arrangement, the detail needs review before cutting. The route may need to move to a location with an approved solution.
If a standard electrical floor box is already in place, inspect its listing and construction. It may have sharp internal edges, limited access, or no approval for tubing. Do not assume it can be repurposed; select a compatible assembly or obtain approval for the specific detail.
Conclusion
An external radiator tubing pass-through is a protected, serviceable route for PC coolant hoses through a floor. The right design comes from the floor assembly, hose manufacturer’s limits, equipment clearances, and applicable fire and electrical requirements, not from a standard opening dimension.
Before work begins, confirm the route, avoid unapproved cuts to structural members, protect hose contact points, keep fittings accessible, and use the required listed firestop system. If any of those conditions cannot be verified, stop and get qualified review.
FAQ
These answers apply to PC liquid-cooling hoses routed through a floor. Local code adoption, the floor assembly, and product instructions still govern the final installation.
What is an external radiator tubing pass-through?
It is a protected floor opening or box that routes coolant hoses between a PC and a radiator in another location.
Is a floor box the same as a pass-through?
Not always. A floor box may house electrical devices, while a pass-through is intended to protect a route. Check the product’s listing and approved use.
Can I use a standard electrical floor box for coolant hoses?
Not by assumption. It may not be listed for liquid hoses, and its edges or shape may damage tubing. Confirm suitability or use an approved alternative.
What size should the opening be?
There is no universal size. Base it on hose outside diameter, fitting envelope, bend space, and the selected pass-through or firestop system.
What bend radius should I use?
Use the minimum bend radius published by the hose manufacturer. Do not pinch, flatten, or force the hose at the box.
Do I need firestopping?
If the floor is a rated assembly, use a firestop system listed for that floor construction and penetrant. Confirm local requirements before cutting.
Can I seal the opening with spray foam?
Not as a replacement for a required listed firestop system. Use the system specified for the actual rated assembly.
Can I drill through a joist to route the hoses?
Only after checking the member-specific limits and obtaining required approval. Do not cut or notch joists, trusses, or engineered members on guesswork.
How do I protect hoses from damage?
Use a compatible sleeve or pass-through, protect all contact edges, support the hose, and keep it within the maker’s bend limit.
How do I check the installation before closing the box?
Inspect the route, bends, supports, fitting access, fan clearance, and required firestop. Then follow the cooling-system maker’s leak-check instructions before concealing the route.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
