Gas Line Sizing for Tankless Water Heaters
BTU demand calculator, CSST vs rigid pipe selector, FL permit guide — size your gas line right the first time.
Pipe Sizing Quick Reference
Natural Gas — 0.5" WC pressure drop, specific gravity 0.60.
| Pipe Size | 10 ft | 50 ft | 100 ft | Max BTU |
|---|---|---|---|---|
| ½" | 172k | 95k | 66k | 172k BTU |
| ¾" | 360k | 199k | 138k | 360k BTU |
| 1" | 678k | 374k | 259k | 678k BTU |
| 1¼" | 1,290k | 714k | 494k | 1.29M BTU |
| 1½" | 1,960k | 1,080k | 748k | 1.96M BTU |
Common FL Tankless Models — BTU Reference
Rinnai RU199iN / RU199eN — NG, 199,000 BTU, 9.8 GPM. Most popular residential. Requires ¾" gas min. 2" PVC or stainless exhaust. FL rebate eligible.
Navien NPE-240A2 — NG/LP, 199,900 BTU, 11.2 GPM. Built-in recirculation pump. Popular in FL for solar-assist systems. ¾" gas line minimum.
Takagi T-KJr2-IN — NG, 140,000 BTU, 6.6 GPM. Compact, good for 1–2 bath homes. ½" gas acceptable under 25 ft. Budget-friendly FL option.
Rheem RTG-84XLN — NG, 180,000 BTU, 8.4 GPM. Most sold at FL big-box stores. ¾" gas required. ENERGY STAR certified, utility rebate eligible.
FL Gas Code — Tankless WH Requirements
Florida requires a permit for ALL gas appliance installations — including tankless water heater replacements. No exceptions under FPC 106.
Pull a Plumbing/Gas Permit (FPC 106.1) — Required for new tankless installation, gas line extension, and meter upgrades. Submit load calculation showing BTU demand. Florida does NOT allow unlicensed gas work.
CSST Bonding (NFPA 54 / FL Amendment) — All CSST must be bonded with #6 AWG copper wire to electrical panel ground. Florida enforces this strictly — it is code, not optional. Required within 6 ft of meter.
Flexible Connector at Unit (ANSI Z21.69) — Appliance connector must be listed, max 3 ft, cannot pass through walls. Must be stainless corrugated type — rubber hose prohibited for FL installations.
Seismic Shut-Off Valve — Not required in FL (no seismic zone), but excess-flow valve (EFV) is recommended by utilities. Many FL gas utilities (FPL, TECO) require EFV at meter on new installs.
Venting — Direct-Vent Required (FL IRC G2427) — Must use manufacturer-approved direct vent or power vent. Category III or IV stainless flue. Cannot vent into chimney with other appliances unless listed for combined use.
CO Detector (FL SB 528) — Required in all sleeping areas within 10 ft if gas appliance installed after 2012. Tankless WH replacement triggers inspection for CO detector compliance.
Pressure Test (FPC 406.4) — All new gas piping must be pressure-tested at 1.5× design pressure minimum — typically 3 PSI for residential. Test must be witnessed by inspector. New CSST runs require separate pressure test.
Water Heater Permit Placard — FL law requires completed permit placard attached to unit. Annual inspection not required, but placard must remain visible per FL Statute 553.73.
CSST vs Black Iron — FL Comparison
CSST (Corrugated Stainless Steel Tubing) — Faster install, must bond, flexible. Best for retrofit in FL concrete block homes. Runs around corners, through walls without fittings. Bonding required at entry point. Approved brands: Gastite, TracPipe, CounterStrike. Do NOT use CounterStrike in exterior exposed locations (UV).
Black Iron Pipe / Schedule 40 — Most common, no bonding issue, more fittings. Standard for exposed or mechanical room runs. Requires pipe dope or yellow Teflon tape on all fittings. FL humidity causes exterior rust — paint or coat exposed runs. Cannot use in direct contact with concrete slab.
PE (Polyethylene) — Underground Only — Used for utility company service laterals and exterior yard runs. Cannot penetrate building without transition to metallic pipe at entry point. HDPE is not permitted for gas in FL.
Pre-Inspection Checklist
- Gas permit pulled from local building department
- BTU load calculation submitted with permit application
- CSST bonded with #6 AWG copper to electrical ground
- Listed appliance connector, max 3 ft, not through wall
- Pressure test completed at 1.5× design pressure (3 PSI min)
- Direct vent or power vent properly terminated exterior
- CO detector within 10 ft of all sleeping areas
- Shut-off valve within 6 ft of unit, accessible
FL Gas Line Sizing — Cost Guide
- Gas line extension (10–25 ft): $350–$650
- Gas line extension (25–50 ft): $600–$1,100
- Gas line upgrade (upsize run): $800–$1,800
- Meter upgrade (utility coordinated): $200–$500 + utility fee
- CSST bonding (existing system): $250–$450
- Full install (tankless + gas line): $1,800–$4,500
- Permit fee (FL average): $85–$250
- FL FPU / TECO meter upgrade fee: Often waived for high-BTU