Combination Listings and the Mix-and-Match Trap

Why this matters

Some things are tested and listed only as a combination: a set of parts that passed together, in a stated arrangement, and that nobody evaluated in any other arrangement. Build the same function out of parts that each carry a mark and the result can be unlisted, because the marks belong to the parts and the test belonged to the set. It is the most common way a careful tech ends up with a failed inspection or a failed system while holding a receipt for nothing but certified products. The cure is a habit: when the job is a system, look up the system before you look at the parts.

What a combination listing is

A combination listing, sometimes called a system listing, is a listing in which the thing evaluated is an assembly of named components in a named arrangement. The listing names each component, often by manufacturer and catalog designation, and the limits of the arrangement: sizes, distances, materials, orientations. Change any named element and you are outside the listing even if your substitute carries its own mark, because your substitute was never tested in that position, with those neighbors.

The underlying rule is the one the codes group already owns: listed equipment is installed per its listing and instructions (see related: The Installation Instructions Are Part of the Code). A combination listing is that rule applied to a set rather than a single product.

Where combinations show up in residential work

Siblings in this group cover three of these in depth, and they get a line each here.

• Matched heating and cooling systems. An outdoor unit, indoor coil and furnace or air handler are rated and certified as a combination. See related: The AHRI Certificate and Matched Systems.
• Vents listed with the appliance. Many appliances specify the vent system that is part of their listing. See related: Venting Systems Listed With the Appliance.
• Breakers listed for a panel. The panelboard's label names the breakers it accepts. See related: Breakers the Panel Label Permits.
• Shower valves and trim. A pressure-balancing or thermostatic shower valve's scald protection is certified for the valve body with its matching trim and cartridge. A different maker's trim that physically fits a rough valve can leave the protection uncertified, and the plumbing code's requirement for scald-limiting valves, as adopted, is met by the certified combination.
• Garage door openers and entrapment protection. The photo eyes or edge sensors that provide the opener's required entrapment protection under UL 325 are evaluated for use with that operator. An unrelated sensor that wires up and lights its LED is not part of the evaluated system, and 16 CFR Part 1211 makes UL 325's entrapment requirements a federal rule for residential operators sold in the US.
• Wire connectors. A connector listed for joining aluminum to copper is listed for specific conductor combinations, sizes and counts printed on its carton. A combination outside the chart is outside the listing.
• Firestop systems. The penetration of a fire-rated wall or floor is protected by a tested system, not by a fire-rated product. This one is the deep case below, because it is the trap trades other than the fire trade fall into most often.

Firestop systems, the purest case

Where the adopted building code requires a penetration of a rated assembly to be protected, the protection is a through-penetration firestop system tested to ASTM E814 or UL 1479, which are fire tests of the whole arrangement. In the IRC, the requirement appears for penetrations of the fire-resistance-rated separation between dwelling units in two-family dwellings (R302.4.1 in the 2021 edition, as adopted), with a prescriptive exception for certain noncombustible penetrants, such as steel, iron or copper pipe, protected as that section describes. In the IBC, it is Section 714, as adopted.

The tested system fixes almost every variable, and the fire-rated sealant on the shelf is one of them, not the system:

ILLUSTRATIVE HALF SECTION - pipe through a rated wall

 SIDE A                                  SIDE B
 gypsum |          stud cavity          | gypsum
 -------+                               +-------
 sealant| <- depth set by the system -> |sealant
 -------+-------------------------------+-------
   PIPE: material, size and wall set by system
 -------+-------------------------------+-------
   ^                                         ^
   annular space at each face: the gap between
   pipe and cut gypsum, min and max per system

Beyond what the drawing shows, the system also names the wall or floor construction it was tested in (stud type, gypsum type and number of layers, hourly rating), any packing or backing material, whether the fill goes on one side or both, and the ratings achieved: an F rating (how long it stopped flame passage) and, where required, a T rating (how long it held the unexposed side below a temperature rise limit).

The mix-and-match version. A tech grabs a tube labeled "fire-rated sealant", fills around a pipe and walks away. The tube carries a genuine mark. The penetration is not protected by a listed system unless that sealant, at that depth, around that pipe, in that annular space, in that wall construction, matches a published system. Every one of those is a variable the fire test held fixed.

Worked example: two penetrations through a two-family separation wall

A plumbing shop is adding a laundry in a two-family house. The new drain and supply run through the 1-hour separation wall between the two units. Values for the system below are illustrative, labeled as read from one system listing; real systems differ and the listing you use governs.

The plan. A 3 in PVC drain and a 3/4 in copper supply line through the wall, each in its own hole. The crew has a tube of fire-rated sealant on the truck.

Look up the systems first. The crew searches the sealant maker's published systems for this wall: wood studs, one layer of 5/8 in type X gypsum each side, 1-hour rated.

Copper line. A system is found for metallic pipe up to 4 in nominal with this sealant: annular space 0 to 1/2 in, sealant 5/8 in deep at both faces, F rating 1 hour. The crew cores the hole so the copper sits with about a 1/4 in gap all round, which is inside 0 to 1/2 in, and fills 5/8 in at both faces. Inside the system. (The IRC's prescriptive exception for copper pipe would also be available where its own conditions are met; the crew uses the system because it is the one they can document.)

PVC drain, first attempt. The only system using this sealant with plastic pipe covers PVC up to 2 in nominal. The drain is 3 in, so the sealant cannot be used for it, however well it is applied. The mark on the tube is real; the combination does not exist.

PVC drain, the fix. The crew finds a system for 3 in PVC in this wall type that uses an intumescent wrap strip around the pipe within the hole, plus sealant at the faces, with an annular space of 0 to 1/4 in. Plastic pipe needs the intumescent because it melts away in a fire and leaves an open hole, which the wrap expands to close. The crew cuts the hole for a tight fit, wraps the pipe to the system's stated number of layers, and seals both faces. Material for the wrap had to be ordered: half a day lost. Rework avoided: cutting out a failed penetration, re-patching rated gypsum and re-inspecting.

Hazard on this job. Cutting and coring the gypsum releases dust that carries respirable crystalline silica if the board has a silica-bearing filler, and the shop treats it as such: a shroud with vacuum extraction on the hole saw, and a respirator under the shop's written 29 CFR 1910.134 program where extraction cannot keep the dust down. Sealants and intumescent products carry their own SDS, which names their ventilation and skin requirements; the crew reads it before opening the tube.

Result. Two penetrations, two different systems, one of which could not have been built from what was on the truck. The tube of sealant was certified and would have produced one compliant penetration and one non-compliant one. The record shows both system designations, the measured annular spaces, the sealant depths and photos of both faces before the walls closed.

What changes the answer

Unrated walls. Most walls in a single-family house are not rated, and there is no firestop system to match. Fireblocking in concealed spaces is a separate code requirement with its own approved materials, not a tested system.

An official's engineering judgment. Where no tested system fits a penetration, many officials will consider an engineering judgment from the firestop maker, a written assessment of a variation from a tested system. It is a request for approval, not a substitute for one. See related: How to Request Approval for an Alternative Method.

A sibling combination with its own document. For heating and cooling, the combination's document is a certificate, not a system drawing, and it has its own logic. Read the right card rather than generalizing from this one.

How to verify a combination is intact

For any system, write the listing or system designation on the job record and list every component it names next to the component you installed, with catalog numbers. Then list every dimension or limit it names next to what you measured. Any line where your component or measurement differs means you are outside the combination, whatever the marks on the parts say.

References

• ASTM E814 and UL 1479, fire tests of through-penetration firestops; International Residential Code R302.4.1 (2021 edition) and International Building Code Section 714, as adopted by your jurisdiction
• UL 325 and 16 CFR Part 1211, entrapment protection for residential garage door operators
• Firestop manufacturer published system listings and the certifying lab's directory of tested systems
• 29 CFR 1910.134, respiratory protection, for cutting gypsum
• See related: Listed, Labeled and Approved: Three Words That Are Not the Same; What an Equipment Listing Actually Covers