3.1 CSST Installation

Quick Answer

On the Massachusetts journeyman plumber PSI exam, treat CSST as a Board product-accepted tubing system, not as generic steel pipe and not as a yellow appliance connector. Install only the manufacturer’s listed fittings after manufacturer training the Board will accept. Size and run CSST at not more than 14 inch water column (0.5 PSIG). Never land CSST on an exterior meter. Where buried CSST has to come up outside the building, cover every exposed inch with metal — not plastic. Bond the gas piping as NFPA 54 7.13.1 requires; if the manufacturer also wants a lightning bonding jumper that is electrical work, the gas inspector needs proof an electrical permit was pulled before the gas job can be signed off.

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The PSI written outline puts CSST in the 21-item gas-piping domain. Massachusetts does not leave CSST to a national installation booklet. 248 CMR 5.05(8) replaces NFPA 54 5.6.3.4 in full, 248 CMR 5.07 adds partition strike protection and bonding language, and the Board’s published policies on corrugated stainless steel tubing and on CSST installed above ground exterior to a building sit on the same Mass.gov policies list as 248 CMR 5.00. Independent prep for this exam means those Massachusetts numbers, not a manufacturer’s two-pound sizing chart from another state.

What CSST is — and what the Board will accept

Corrugated stainless steel tubing is a listed fuel-gas tubing with a corrugated stainless steel core and a polymer jacket. It is joined with mechanical fittings made for that brand. 248 CMR 5.03 ties “listed” equipment to Board product-acceptance under 248 CMR 3.00. 248 CMR 5.09 repeats the same gate for appliances, equipment, and accessories: only products that meet 248 CMR 3.04(1) may be used in gas fitting unless the Board has waived product acceptance. The policies list therefore carries both the CSST product-acceptance / design-standard entry and the CSST installation policies. A roll of tubing that is listed to ANSI LC 1/CSA 6.26 still is not legal in the Commonwealth until that product, and the installation instructions that travel with it, have gone through the Board.

248 CMR 5.05(8)(a) is the first exam trap. All fittings and accessories shall be approved by the CSST manufacturer for use with their system. Mixing Brand A tubing with Brand B nuts is a fail. The same paragraph limits installation to licensees who have completed manufacturer training/certification acceptable to the Board. A journeyman card without that manufacturer credential is not enough for a CSST rough.

248 CMR 5.05(8)(m) then stacks two rulebooks: manufacturer instructions and 248 CMR 3.00 through 7.00. Where the booklet is looser than Massachusetts, Massachusetts wins. A December 2017 Board discussion of OmegaFlex and ANSI LC 1 still ran into the Massachusetts cap in 5.05(8)(l) — CSST systems shall be sized and installed with a maximum 14 inch water column (0.5 PSIG) gas pressure. That is not a suggestion. It is why “2 psi CSST” answers that work in other jurisdictions are wrong here.

Bonding and grounding as Massachusetts actually writes them

Lightning arcing can puncture thin-wall CSST. The Board said so in the Corrugated Stainless Steel Tubing policy (enacted February 4, 2009; posted with the 2017 policy set). After a temporary rescission of product approval in November 2008, the Board reinstated accepted CSST products with two mitigation stories manufacturers had documented at Lightning Technologies in Pittsfield: a bonding jumper, and for at least one OmegaFlex product, a special jacket. The same policy is blunt about license lines. Using a bonding jumper with CSST falls outside the scope of plumbing and gas fitting. Licensed electricians, under the Board of Fire Prevention Regulations, have exclusive jurisdiction over that extra bonding. If the manufacturer’s instructions require a jumper, the work is done under the electrical code, including pulling any required electrical permits.

248 CMR 5.07(5) put that split into the fuel-gas amendments. CSST systems shall be bonded in accordance with NFPA 54 7.13.1 unless that bonding would conflict with the manufacturer’s installation instructions. Additional bonding that is electrical licensure work is not governed by 248 CMR. The installation may not be approved by a plumbing or gas inspector unless there is proof that an electrical permit has been obtained to perform such bonding. On a closed-book item, do not write that the plumber “must land the #6 jumper.” Write that the gas piping is bonded as 7.13.1 requires, and that extra manufacturer lightning bonding is electrical work that must be permitted before gas approval.

Strike protection, partitions, and support intervals

CSST is easy to nail. 248 CMR 5.07(3) adds 7.3.4.1 and Table 7.3.4.1 for tubing in concealed wall spaces and partitions. Read the table by orientation, insulation, and size.

Two field habits the table kills: stapling small CSST tight to studs in an empty vertical bay, and concealing 1 inch-and-up CSST without a manufacturer shield the full run. Interior hanger spacing that is not in Table 7.3.4.1 comes from the manufacturer instructions that 5.05(8)(m) already made mandatory — do not invent a statewide “every four feet” number the Board did not print.

Roof support is statewide. 248 CMR 5.05(8)(q) allows CSST to roof-top equipment only by listed methods. UV-stabilized jacket tubing may be fastened to a wooden plank or steel channel that is attached to the roof structure every six feet, with the tubing itself attached to that support every six feet. Or the tubing rides in metal or plastic conduit attached every six feet; if a tee is needed, the sleeve stops no more than 12 inches from the tee on both runs and the branch. For 1.5 inch and 2 inch UV-jacket CSST, blocks spaced not more than 48 inches are allowed if they are outdoor-rated, attached to the roof, and do not damage the jacket. The maximum unsupported length to a gas-fired roof-top unit or similar equipment is 30 inches. 248 CMR 5.07(2) adds that rooftop supports must not compromise the roof; structural repair of the roof is not gas-fitting work.

Fixed appliances inside the building have a related 30 inch rule. 5.05(8)(i) allows CSST to a fixed appliance only when the tubing is securely attached to the structure, does not run exposed for a distance greater than or equal to 30 inches without being physically attached, and terminates with a proper fitting and gas cock.

Prohibited locations and the above-ground exterior policy

Memorize the hard nos.

• Exterior meters (5.05(8)(e)): No CSST shall be connected to an exterior meter. Terminate at the foundation wall with a termination fitting. Rigidly connect the meter to the building with steel piping.
• Appliance connectors (5.05(8)(k)): CSST shall not be used as a flexible appliance connector downstream of the appliance shutoff device. A listed yellow connector or the fixed-appliance rules in (i) are different animals.
• Concealed assembled manifolds (5.05(8)(g)): Only manifolds supplied and listed by the CSST manufacturer may be concealed. An assembled manifold of close nipples and malleable tees shall be accessible.
• Concealed fittings (5.05(8)(b)): Concealed joints use only CSST fittings listed for concealed spaces and produced by that CSST manufacturer. Malleable fittings may be concealed in combination with CSST fittings, with only a single CSST connection per malleable fitting.
• Concealed repairs (5.05(8)(c)): Repair with a listed fitting for that system and install an access panel at the repair.
• Fireplaces (5.05(8)(h)): CSST stops with a termination fitting at the entrance to the masonry fire box, finished so the termination is not left in a damaging environment.
• Decks (5.05(8)(f)): Sleeve CSST through a metal or concrete deck with Schedule 40 black or galvanized pipe extending a minimum of six inches above the finished floor and below the underside of the deck. Any fire-stopping is a 780 CMR building-inspector issue, not the plumbing inspector’s 248 CMR 3.01 job.

Underground CSST (5.05(8)(j)) sits in a sleeve that can take the load. Except for Board product-accepted pre-engineered sleeves, the sleeve shall allow free movement. Seal sleeve ends liquid tight. Place warning tape no more than six inches from the top of grade. Minimum cover is 18 inches from the top of grade.

When that buried run has to come up outside the building, the Board interpretation CSST Installed Above Ground Exterior to a Building (enacted November 6, 2013) applies. The exposed rise is treated as above-ground piping that must be securely supported and protected from physical damage, with wall penetrations coated or wrapped and any sleeve annular space sealed against water, insects, and rodents. To protect the exposed CSST, some type of metal covering must surround it or be attached to the building so it covers all exposed portions. Plastic pipe will not accomplish this. The interpretation notes that plastic gas pipe itself is an underground-only material (with the anode-less steel-cased riser exception). Using plastic as a “cover” over above-ground CSST is therefore inadequate. After a pressure test, any jacket that was stripped for a fitting outdoors is recovered with manufacturer-specified tape (5.05(8)(p)).

Interior meters are the contrast item. 5.05(8)(d) allows a direct CSST connection if the meter is securely affixed to the building and the CSST is secured to the structure when 24 inches or more of tubing is exposed.

Fittings, pressure, transition to rigid pipe, inspection issues

Transition to rigid pipe is not optional decoration. Exterior meters must go steel-to-structure, then a termination fitting, then CSST indoors. Fireplace boxes must see a termination fitting, not a corrugated run into the fire. Regulator and relief vent lines that are CSST (248 CMR 5.09, 9.1.19.1) shall not penetrate roofs or sidewalls; they transition to steel or wrought iron no less than one foot inside the building. That is a CSST-to-rigid rule even though the gas in the vent line is not the appliance supply.

Inspection is front-loaded. 5.05(8)(n) requires a test before any piping is covered on new construction or remodeling, as part of the required inspection. The licensee then does a second test before connecting any appliance. A tag affixed to the meter or service manifold, signed and dated by the licensed plumber or gas fitter, acknowledges that second test. 5.05(8)(o) bans corrosive leak fluids — household soaps and detergents can attack CSST and fittings. The Chapter 8 inspector-witnessed pressure numbers still apply; CSST does not get a weaker test because it is flexible. Common inspection failures are mixed-brand fittings, CSST landed on an outdoor meter, 2 psi CSST, missing strike plates, assembled manifolds buried in a wall, plastic “protection” on an exterior rise, jacket left stripped after an outdoor joint, and a gas final requested before the electrical bonding permit exists.