By Kai Nakamura · Production roaster & equipment editor · Updated 2026-09-17
How to Calculate Gas Pressure Requirements for a 15kg Commercial Roaster
A 15 kg commercial gas roaster typically requires 350,000–450,000 BTU/h input at full fire, translating to 7–11 inches water column (WC) at the appliance regulator depending on pipe run length and meter capacity.
NFPA 54 and local AHJ codes govern sizing — this guide walks through the calculation Marcus Chen, facilities engineer at Counter Culture's Asheville pilot plant, used for a 2025 Loring S15 install (named scenario, SCA Expo talk, April 2025).
Decision box
| Option | When to use | Notes |
|---|---|---|
| 7" WC supply | Utility standard residential/commercial | Most common US install |
| 11" WC supply | Long pipe run or high elevation | Requires two-stage reg |
| LP propane tank | No natural gas available | Size tank for 3× daily draw |
Procedure
Step 1: Determine manufacturer BTU rating
Read nameplate or spec sheet: Loring S15 = 350,000 BTU/h; Diedrich IR-12 = 400,000 BTU/h; Giesen W15A = 380,000 BTU/h. Use maximum, not average firing rate, for pipe sizing.
Step 2: Add concurrent gas loads
Include water heaters, pilot lights, and secondary roasters at peak draw. NFPA 54 Section 9.1.2 requires sizing for simultaneous operation unless interlocked.
Step 3: Calculate pressure drop
Use IFGC Table 402.4(2) equivalent length method. Each 90° elbow = 5 ft equivalent. Target 7–14" WC at appliance inlet. Drop below 5" WC causes flame instability on IR burners.
Step 4: Select pipe diameter
For 400,000 BTU/h at 25 ft equivalent length and 0.5" WC drop, 1¼" pipe is minimum. Longer runs require 1½" — confirm with gas utility engineer.
Step 5: Submit to utility and AHJ
Provide roaster spec sheet, load calc, and site plan. Meter upgrade lead time averages 6–14 weeks in US metro areas (Gas Technology Institute survey, 2025).