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Building Code Reference

Got a CMC 310.1 correction?

Condensate disposal

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CMC 310.1 is the California Mechanical Code section that requires condensate from air-cooling coils, condensing appliances, and similar equipment to be collected and discharged to an approved plumbing fixture or disposal area, through an indirect waste pipe sloped at least 1/8 inch per foot and sized per Table 310.3. Where the equipment sits in a space that overflow could damage, CMC 310.2 adds a second layer of protection. This section is cited on nearly every residential and light-commercial HVAC permit where condensate drainage details are missing or incomplete on the submitted drawings.

How to fix it

  1. Show the primary condensate drain line and discharge point on the mechanical plan

    On the mechanical plan sheet, draw the primary condensate drain line from the air handler to its discharge point. Label it as the primary condensate drain. Identify the discharge point explicitly, such as the sanitary sewer via an indirect waste receptor (air gap required), an approved floor drain, or an approved exterior disposal area that will not pool near the foundation or drain over a public way. The plan-checker needs to see the start point, pipe routing, and end point to confirm the line is code-compliant. A note that says "drain to outside" is not sufficient without showing the route and the termination point.

  2. Specify the primary drain pipe diameter and minimum slope

    Call out the primary drain pipe diameter and the slope on the plan or in a mechanical schedule. Table 310.3 sets the minimum size by capacity: 3/4 inch up to 20 tons, which covers most residential split systems, and PVC is permitted below 1-1/4 inches. The run must slope at least 1/8 inch per foot toward the discharge point. If the line has to travel a long horizontal distance, confirm the slope is maintainable along the entire run before finalizing the routing. When the plan omits pipe size and slope, the reviewer has no compliance path to check against and will send a correction asking for both.

  3. Add secondary overflow protection for attic and ceiling-mounted air handlers

    For any air handler installed in an attic, above a finished ceiling, or anywhere a primary drain blockage would cause water damage to occupied space or structure, you must provide secondary overflow protection. CMC 310.2 offers four options: a water-level device that shuts the unit off, a watertight secondary pan with its own drain, a secondary drain line set above the primary connection, or a pan with a water-level shutoff. Added drain lines must be at least 3/4 inch and discharge where readily observed. Show whichever method you are using on the plan. If using a secondary pan, note the pan dimensions, the pan drain line size, and the discharge point. If using a secondary drain line terminating outside, show the termination point on an exterior elevation.

  4. Show the condensate pump and overflow safety switch when gravity drainage is not possible

    When the air handler sits below the approved discharge point and gravity flow is not possible, a condensate pump can be used where the Authority Having Jurisdiction approves it. Show the pump location on the mechanical plan and call out the pump capacity in gallons per hour. Note the discharge line routing from the pump to the approved discharge point. CMC 310.1.1 requires the pump discharge to rise to a gravity drain and each unit to have its own sump interlocked to keep the equipment from running during a failure. Show the float switch and its connection to the system control circuit on the plan. A pump alone does not satisfy the secondary protection requirement.

  5. Verify the discharge location qualifies under CMC 310

    Confirm the discharge point you have shown is an approved plumbing fixture or disposal area. Into the drainage system, CMC 310.5 requires an indirect connection through an air gap or air break to a trapped and vented receptor, dry well, mop sink, leach pit, or fixture tailpiece. Condensate cannot drain over a public way, and an attic without a receptor is not a disposal area. Some cities have local amendments that further restrict exterior condensate discharge, particularly in water-sensitive areas. Check the adopted local amendments for your jurisdiction before finalizing the discharge point.

  6. Add a condensate drainage note to the mechanical plan or schedule

    Add a note on the mechanical sheet that explicitly references the key items: primary drain destination, secondary overflow method, pipe sizes, and slope. Something like: "Condensate drainage per CMC 310. Primary 3/4-inch PVC drain to [location]. Secondary overflow pan/drain to [readily observed location]. All horizontal runs at 1/8-inch per foot minimum slope." This gives the plan-checker a checklist they can verify against the section without hunting through the plan set. It also documents the design intent for the inspector at rough-in.

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Why you got flagged

Plan-checkers flag CMC 310.1 most often when the mechanical plan shows the air handler location but says nothing about where the condensate goes. The drainpipe destination has to be called out explicitly on the drawings. Writing "condensate per code" in a note does not cut it. The reviewer needs to see the line routing and the approved discharge point before they can sign off.

A second common trigger is the missing secondary drain or overflow pan. CMC 310.2 requires an additional overflow protection method when the equipment is installed where condensate overflow could cause damage, which covers almost every attic or ceiling-mounted air handler. Plans that show only the primary drain get a correction asking for the secondary pan or secondary drain line, whichever applies to the installation.

Undersized or unspecified primary drain lines also draw corrections. Table 310.3 sets the minimum pipe size by cooling capacity (3/4 inch up to 20 tons, 1 inch from 21 to 40 tons), and CMC 310.1 requires a slope of at least 1/8 inch per foot. When the plan shows a drain line without specifying size or slope, the reviewer has no way to confirm compliance and kicks it back.

Finally, the discharge location itself matters. Condensate has to go to an approved plumbing fixture or disposal area, and it cannot drain over a public way. Where it connects to the drainage system, CMC 310.5 requires an indirect connection through an air gap or air break to a trapped and vented receptor, dry well, mop sink, leach pit, or fixture tailpiece. If the plans route condensate somewhere that does not qualify, you will get a correction calling for a redesign of the discharge point.

The official code

2025 California Mechanical Code Section 310 Condensate Wastes and Control (310.1 Condensate Disposal), via California Building Standards Commission

Read the source →

Common questions

Does CMC 310.2 require a secondary drain pan on every air handler?
Not every air handler, but most attic and ceiling-mounted units will need some form of it. CMC 310.2 requires an additional overflow protection method wherever equipment is installed in a space where condensate overflow could cause damage. A secondary pan is one of four options: the others are a water-level device that shuts the unit off, a separate drain line set above the primary connection, or a pan with a water-level shutoff. If the unit is in a mechanical closet on a concrete slab with a floor drain, you can make the case that a primary-only drain is sufficient. In practice, plan-checkers will call for secondary protection on any attic-mounted unit unless the plan clearly shows why it is not needed.
Can condensate discharge to the ground outside?
It can, if the location is an approved disposal area. CMC 310.1 requires condensate to discharge to an approved plumbing fixture or disposal area and bars it from draining over a public way, so the discharge should not create a nuisance or pool near the foundation. The secondary drain is different: CMC 310.2 requires it to discharge at a point that is readily observed, so a dripping secondary line signals a primary drain failure and someone calls for service. Some local amendments tighten exterior discharge. Check your specific city's adopted amendments, especially in water-sensitive areas.
What pipe size does the primary condensate drain need to be?
CMC Table 310.3 sizes the condensate pipe by equipment capacity: 3/4 inch up to 20 tons, 1 inch from 21 to 40 tons, 1-1/4 inches from 41 to 90 tons, 1-1/2 inches from 91 to 125 tons, and 2 inches from 126 to 250 tons. Most residential split systems fall in the 3/4-inch row. CMC 310.1 requires a slope of at least 1/8 inch per foot, and the pipe cannot be smaller than the equipment outlet. Below 1-1/4 inches, PVC, CPVC, and other approved rigid materials are permitted. Always cross-reference the equipment manufacturer's installation instructions.
Does a condensate pump satisfy the secondary drain requirement?
A condensate pump handles primary drainage when gravity is not available, but it does not substitute for overflow protection on its own. If the pump fails, water will still back up and overflow. CMC 310.1.1 requires each unit to have its own sump interlocked to keep the equipment from running during a pump failure, and CMC 310.2 still applies where overflow could cause damage. A water-level device that shuts the unit off is one of the 310.2 options. Show both on the plan: the pump, the shutoff device, and its connection to the system control.
My corrections letter says to show drainage to an approved location. What counts?
CMC 310.1 calls for an approved plumbing fixture or disposal area. Into the drainage system, CMC 310.5 lists an indirect connection through an air gap or air break to a trapped and vented receptor, dry well, mop sink, leach pit, or the tailpiece of a plumbing fixture. What does not qualify: draining over a public way, into an undraining pan in the attic, or to any location that creates standing water or a nuisance. If you are unsure which option fits your building layout, an indirect waste connection to the building sanitary drain is the most universally accepted approach and rarely draws a follow-up correction.
Does CMC 310 apply to mini-split systems?
Yes. Mini-split wall-mounted and ceiling cassette units produce condensate just like ducted systems, and CMC 310.1 covers condensate from air-cooling coils, which includes mini-split indoor units. Mini-splits get flagged at the same rate as ducted systems. The rules are identical: show the drain line, the pipe size, the slope, the discharge point, and secondary overflow protection if the unit is located where overflow would damage the structure. Many mini-split submittals miss the condensate detail because contractors assume it is minor, and it often comes back as a correction.
Can one drain line serve as both the primary and secondary drain?
No. A single drain line is the primary drain. It cannot double as the secondary. The purpose of secondary overflow protection is to handle condensate if the primary line clogs. If both are the same pipe, a blockage defeats both protections at once. CMC 310.2 calls for an additional separate drain line, connected higher than the primary drain connection and discharging at a point that is readily observed, so occupants can see when the primary has failed. Combining them gets flagged on plan check and at inspection.

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