CSST Gas Sizing Chart
Sizing corrugated stainless steel tubing (CSST) for natural gas by EHD flow rating and developed length. CSST is sized by EHD, not nominal pipe size — a higher EHD carries more gas. Capacities are in CFH at the standard 0.5 in. w.c. pressure drop; values are manufacturer-typical (Gastite/FlashShield), and you must use your own brand’s listed table.
CSST natural gas capacity (CFH)
| EHD (nominal) | 10 ft | 25 ft | 50 ft | 100 ft |
|---|---|---|---|---|
| 13 (3/8") | 32 | 20 | 14 | 10 |
| 18 (1/2") | 93 | 59 | 42 | 30 |
| 23 (3/4") | 183 | 120 | 87 | 63 |
| 31 (1") | 415 | 267 | 191 | 137 |
| 37 (1-1/4") | 620 | 396 | 282 | 201 |
| 47 (1-1/2") | 1304 | 830 | 590 | 419 |
| 60 (2") | 2711 | 1690 | 1183 | 827 |
EHD is a flow rating, not a size
The single thing to understand about CSST is that its sizing number, EHD, describes how much gas the tubing flows, not its physical diameter. That is why you cannot read a CSST run like black pipe: two brands' "3/4-inch" tubing can carry different amounts, and each is assigned its own EHD. Total the connected load — from the appliance BTU demand chart — convert to CFH, take your longest developed length, and pick the EHD that covers it in the manufacturer's table.
CSST must be bonded to the building electrical grounding system per NFPA 54 §7.13 — a 6 AWG (or larger) copper jumper attached downstream of the meter or second-stage regulator, with a UL 467 listed clamp, to guard against lightning-induced arc-through. Arc-resistant (black-jacket) CSST may have different bonding provisions per its listing.
Common questions
How is CSST sized for gas?
By EHD — the Equivalent Hydraulic Diameter, a flow-rating number rather than a pipe dimension. Total the connected gas load in CFH, find your developed length, and read across the EHD table for the tubing that carries it. A higher EHD means more capacity: at 50 ft and 0.5 in. w.c. drop, EHD 23 carries 87 CFH while EHD 31 carries 191 CFH.
Why do CSST tables differ by brand?
Because CSST is manufacturer-specific. Each brand tests and lists its own tubing, so the nominal-size-to-EHD mapping differs — a 3/4" line is EHD 23 in one brand and EHD 25 in another — and even at the same EHD number the tested capacities differ. Always size from the specific manufacturer’s listed table, and never mix brand tables. The table here is Gastite/FlashShield, shown as a representative example.
Does CSST have to be bonded?
Yes. NFPA 54 requires CSST to be bonded to the building’s electrical grounding system with at least a 6 AWG copper jumper, to prevent a lightning strike from arcing through the thin tubing wall. It is a code requirement and a well-known safety issue — arc-resistant (black-jacket) CSST has its own bonding provisions per its listing.
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