Where can condensate from my ADU's mini-split or heat pump water heater drain?

Condensate has to go to an approved plumbing fixture or approved disposal area, through an indirect connection, never piped straight into a drain and never onto a public way. That's the rule in Section 310 of the 2025 California Mechanical Code, and the Plumbing Code has a parallel condensate section (CPC 814). Every ADU with a ductless heat pump or a heat pump water heater needs a planned route for this water.

Where condensate comes from

• Mini-split indoor heads and ducted air handler coils, whenever they cool or dehumidify.
• Heat pump water heaters, which pull moisture out of the air as they heat water.
• Condensing gas appliances, where gas is still used. Their drains have their own requirements (CMC 310.4).

Code rules for the drain line

• Destination: collect condensate and send it to an approved plumbing fixture or disposal area. Where it enters the drainage system, it must go through an indirect waste pipe. It may not drain over a public way (CMC 310.1).
• Slope and material: at least 1/8 inch per foot, in approved corrosion-resistant material (CMC 310.1).
• Size: set by equipment capacity in Table 310.3. Pipe smaller than 1-1/4 inches may be PVC, CPVC, PE, PP, copper, or another rigid material the building official approves.
• Cleaning: configure the line or add a cleanout so you can clear a blockage without cutting the pipe (CMC 310.3.1).
• Indirect connection: condensate lines can't connect directly to the drainage system. They discharge through an air gap or air break into a trapped and vented receptor, dry well, leach pit, or the tailpiece of a plumbing fixture, such as a sink (CMC 310.5).

Condensate pumps

Where gravity can't reach an approved point and the building official approves a pump, install it per the manufacturer, run the discharge up to a gravity drain, and interlock the pump with the equipment so the equipment shuts off if the pump fails (CMC 310.1.1).

Typical ADU solutions

• A wall-mounted head on an exterior wall: a sloped gravity line through the wall to a disposal point your jurisdiction accepts.
• A head on an interior wall: a concealed sloped line to a sink tailpiece or trapped receptor, or a small pump.
• A heat pump water heater in a closet: a short line to a nearby receptor or tailpiece, with the pan drain and relief line routed separately.

What it means for your plumbing plan

Your plans should show each condensate source, its route and slope, where it ends, and any pump with its interlock, coordinated with the mechanical sheets so the head locations and drain routes agree. See mini-split heat pumps for ADUs, our mechanical plans, and our plumbing plans.

Sources: gocodebook.com, gocodebook.com, gocodebook.com.