Plumbing (C-36) · Lesson 6 of 8

Gas Pipe Sizing by BTU and Length

"Gas Pipe Sizing by BTU and Length" is lesson 6 of 8 in the Plumbing (C-36) Learning Hub. It opens with "Two Numbers Drive Every Gas Pipe Size" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Two Numbers Drive Every Gas Pipe Size
  2. Converting BTU/h to CFH
  3. Step 1: Find the Developed Length
  4. Step 2: Add Up Demand for Each Section
  5. Step 3: Read the Table for Pipe Size

The worked example in the course applies this lesson to a realistic job in 4 steps, moving through "Round the developed length up to the next table row", "Convert each appliance's demand to CFH", and "Total demand on the main line from the meter".

What you'll be able to do

  • Explain the main idea of "Gas Pipe Sizing by BTU and Length" in plain language you can use on the exam.
  • Apply this step with confidence: "Step 2: Add Up Demand for Each Section".
  • Apply this step with confidence: "Step 3: Read the Table for Pipe Size".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
GAS PIPE SIZING BY BTU AND LENGTH The longest-length method METER RANGE 65,000 WATER HTR 35,000 FURNACE 50,000 developed length to farthest outlet (the range) = 78 ft CONVERT BTU/h TO CFH CFH = BTU/h / 1,100 Range 65,000 / 1,10059 CFH Water heater 35,000 / 1,10032 CFH Furnace 50,000 / 1,10045 CFH Total main-line demand136 CFH always round CFH up to the next table value READING THE TABLE 1 Find your length row - round UP if not exact 2 In that row, find your CFH - round UP if not exact 3 Pipe size = column header above that cell CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Two Numbers Drive Every Gas Pipe Size

Gas pipe sizing (the longest-length method) always comes down to two inputs: (1) the developed length - the distance from the gas meter to the farthest appliance outlet, following the actual pipe route including fittings, and (2) the total gas demand that section of pipe has to carry, in cubic feet per hour (CFH).

Step 2: Converting BTU/h to CFH

Appliance nameplates list demand in BTU per hour, but the sizing tables are read in cubic feet per hour of natural gas. Convert by dividing: CFH = BTU/h / 1,100. A 65,000 BTU/h range therefore draws about 59 CFH of natural gas.

Step 3: Step 1: Find the Developed Length

Measure the total run of pipe from the meter to the single farthest appliance, including the extra equivalent length fittings and valves add (elbows and tees create friction just like straight pipe). If your measured length falls between two rows in the table, use the NEXT LONGER length row - always round up, never down, when picking the length row.

The remaining 2 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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