6.3 Indirect Waste, Air Gaps, Air Breaks, Waste Receptors & Condensate Disposal

Why some waste is indirect

An indirect waste pipe does not connect directly to the drainage system. It discharges through an air break or air gap into a trap, fixture, receptor or interceptor (IPC Chapter 2). If the drainage system backs up, sewage cannot flow back into food equipment, sterilizers or potable-water devices. 801.2 requires devices that serve special functions, such as sterilization, distillation, processing, cooling or storage of ice or food, to be protected against backflow, flooding, fouling, contamination and stoppage of the drain.

Air gap versus air break (IPC Chapter 2; 802.3.1 and 802.3.2)

The drainage air gap rule has no 1-inch minimum. That number belongs to the potable-water air gap table (608.16.1). A 1-inch indirect waste pipe therefore needs a 2-inch drainage air gap.

Which discharges need which separation (IPC 802.1)

Food-handling equipment (in other than dwelling units), clear-water waste, humidifiers, dishwashing machines, and utensil, pot, pan and dish sinks must discharge through an indirect waste pipe:

Fixtures not required to be indirect are connected directly under Chapter 7.

Related indirect discharges elsewhere in the code:

• 608.4: overflow, relief valve and waste discharge pipes from water pumps, filters, softeners and tanks terminate through an air gap.
• 611.2: reverse osmosis drinking water units discharge through an air gap or an air gap device meeting CSA B483.1 or NSF 58.
• 406.2: clothes washers discharge through an air break into a standpipe.
• 409.4: residential dishwashers may connect to a sink tailpiece wye or disposer, or discharge through an air break to a standpipe.
• 504.6: water heater relief valve discharge uses an air gap in the same room as the water heater.

Installing indirect waste piping (IPC 802.2 and 802.3)

• Materials, joints and connections follow Chapter 7 (802.2).
• Indirect waste discharges through an air gap or air break into a waste receptor, and receptors must be trapped and vented and connected to the building drainage system.
• Trap the indirect waste pipe if it exceeds 30 inches in developed length measured horizontally or 54 inches in total developed length.
• Exception: a receptor that receives only clear-water waste and does not connect directly to a sanitary drainage system needs no trap.

Waste receptors (IPC 802.4)

A waste receptor is a floor sink, standpipe, hub drain or floor drain that receives indirect waste.

• Except for hub drains receiving only clear-water waste and standpipes, the receptor outlet must have a removable strainer or basket.
• Receptors must not be installed in concealed spaces, and not in plenums, crawl spaces, attics or interstitial spaces above ceilings and below floors. They need ready access.
• 802.4.1: size the receptor for the maximum discharge of all pipes it serves, and install it to prevent splashing or flooding.
• 802.4.2: a hub drain is a hub or pipe extending at least 1 inch above a water-impervious floor.
• 802.4.3: standpipes are individually trapped and extend at least 18 inches but not more than 42 inches above the trap weir, with access for rodding.
• 802.4.3.1: a laundry tray waste line without its own trap may connect to a clothes washer standpipe. The standpipe must then extend at least 30 inches above its trap weir and above the laundry tray's flood level rim, and the tray outlet must be within 30 inches horizontally of the standpipe.
• 709.4: a receptor's dfu load is the sum of the fixtures discharging to it.

Condensate disposal (IPC 314)

314.1 fuel-burning appliances: liquid combustion byproducts of condensing appliances go to an approved plumbing fixture or disposal area per the manufacturer. The piping must be approved corrosion-resistant material, no smaller than the appliance drain connection, sloped at least 1/8 inch per foot.

314.2 evaporators and cooling coils:

• 314.2.1: convey condensate from the drain pan outlet to an approved place of disposal, sloped at least 1/8 inch per foot. Condensate must not discharge into a street, alley or other area where it causes a nuisance.
• 314.2.1.1: condensate drains must not connect directly to any plumbing drain, waste or vent pipe. They may discharge only into a floor sink, floor drain, trench drain, mop sink, hub drain, standpipe, utility sink or laundry sink. A connection to a lavatory tailpiece wye or a bathtub overflow does not count as discharging to a fixture. Except where discharging to grade outdoors, the discharge point must be in the same occupancy, tenant space or dwelling unit as the source.
• 314.2.2: approved materials include ABS, cast iron, copper, CPVC, PEX, PE-RT, polyethylene, polypropylene, PVC and PVDF. The drain must be at least 3/4 inch and may not decrease in size. Manifolded drains are sized by Table 314.2.2 (3/4 inch up to 20 tons of refrigeration; 1 inch over 20 to 40 tons; 1-1/4 inch over 40 to 90 tons; 1-1/2 inch over 90 to 125 tons; 2 inch over 125 to 250 tons).
• 314.2.3 auxiliary and secondary drain systems: where overflow from the primary drain could damage building components, provide one of the following:
  1. An auxiliary drain pan under the coil with a separate drain that discharges to a conspicuous point. The pan must be at least 1-1/2 inches deep and at least 3 inches larger than the unit or coil in width and length. Galvanized pans must be at least 0.0236 inch (No. 24 gage), and nonmetallic pans at least 0.0625 inch.
  2. A separate overflow drain line from the equipment's drain pan, connected higher than the primary drain connection and discharging to a conspicuous point.
  3. An auxiliary drain pan without a drain, with a water-level detection device meeting UL 508 that shuts off the equipment before the pan overflows.
  4. A UL 508 water-level detection device in the primary drain line, the overflow drain line or the equipment pan, located above the primary drain connection and below the pan's overflow rim, that shuts off the equipment if the primary drain is blocked.
• 314.2.3.1: downflow units and other coils with no room for a secondary drain or pan need a water-level monitoring device inside the primary drain pan. A device in the drain line does not satisfy this rule.
• 314.2.3.3: the termination of concealed condensate piping must be marked as primary or secondary.
• 314.2.4: condensate drains are trapped as required by the equipment manufacturer. 314.2.4.1: ductless mini-splits need an in-line check valve or a trap.
• 314.2.5: drain lines must be configured so blockages can be cleared without cutting the line.