Refrigeration (C-38) · Lesson 1 of 8

Refrigerant Charge Limit for a Room: RCL from CMC Table 1102.3

"Refrigerant Charge Limit for a Room: RCL from CMC Table 1102.3" is lesson 1 of 8 in the Refrigeration (C-38) Learning Hub. It opens with "What the Concentration Limit Protects" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. What the Concentration Limit Protects
  2. Read the RCL in Table 1102.3
  3. Choose the Volume That Counts
  4. Turn the RCL Into a Pound Limit
  5. When the Circuit Is Over the Limit

The worked example in the course applies this lesson to a realistic job in 7 steps, from "Check the refrigerant and occupancy" through "Institutional comparison".

What you'll be able to do

  • Explain the main idea of "Refrigerant Charge Limit for a Room: RCL from CMC Table 1102.3" in plain language you can use on the exam.
  • Apply this step with confidence: "Choose the Volume That Counts".
  • Apply this step with confidence: "Turn the RCL Into a Pound Limit".
  • Apply this step with confidence: "When the Circuit Is Over the Limit".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Charge Limit for a Room: R-410A ExampleONE CIRCUIT, TWO ROOMS (NOT CONNECTED)CONFERENCE20 x 30 x 9 ft5,400 cu ftOFFICE10 x 12 x 8 ft960 cu ftsmallestIDUIDUOne circuit: 30 lb R-410ASmallest space governs (1104.2.2)RCL LIMIT MATH (CMC 1104.2)Table 1102.3: R-410A, Group A1RCL = 26 lb per 1,000 cu ft (lb/Mcf)Limit = 26 x 960 / 1,000= 24.96 lb allowedCircuit charge = 30 lb30 - 24.96 = 5.04 lb OVER the limitRoom needed = 30 / 26 x 1,000= 1,154 cu ft (round up)Institutional: RCL x 50% = 13 lb/Mcf30 lb > 24.96 lb: NOT permitted as designedCut the charge, serve only larger spaces, or use another approved design (1106.1.1)WHICH VOLUME COUNTS (1104.2.1 - 1104.2.3)Unconnected rooms: smallest room. Open atrium or mezzanine: lowest floor area x 8.2 ft.Ducted: add supply and return ducts; leave out ceiling plenum unless part of the air path.Source: 2025 California Mechanical Code Table 1102.3; Sections 1103.2, 1104.1 - 1104.3, 1106.1.1CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: What the Concentration Limit Protects

A leak in a closed room can displace air or build to a toxic or flammable level. 2025 CMC Section 1104.2 therefore says that in a complete discharge of one independent circuit of a high-probability system, the concentration may not exceed the amount shown in Table 1102.3, called the Refrigerant Concentration Limit (RCL). A system is high-probability when a leak from a failed connection, seal or component will enter the occupied space (Section 1103.2.1); a direct system is the typical example. An indirect closed system is typical low-probability (Section 1103.2.2).

Step 2: Read the RCL in Table 1102.3

Table 1102.3 prints each refrigerant's safety group, OEL in ppm and RCL in lb/Mcf. Mcf is 1,000 cubic feet, so lb/Mcf is pounds of refrigerant per 1,000 cu ft of room. Printed RCL values: R-22 = 13, R-134a = 13, R-404A = 31, R-410A = 26, R-507A = 32, R-744 (carbon dioxide) = 3.4, R-290 (propane) = 0.59. Ammonia R-717 appears as 0.014, but the table note says ammonia systems are not regulated by Chapter 11 (Section 1102.2 sends them to the IIAR standards).

The remaining 3 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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