Most portable ACs made after 2020 use auto-evaporative technology that exhausts collected condensate through the hot air hose — meaning you rarely need to drain them. In dry climates, you may never drain them at all. In humid climates (Southeast US, Gulf Coast, tropical areas), even auto-evaporative units occasionally fill their internal tank and need manual draining every 2–8 hours during peak humidity.
Here's how each drainage method works, how to set up continuous draining, and what to do when the "FL" (full) indicator lights up.
How Portable ACs Generate Water
Every portable AC dehumidifies as it cools. Warm, humid room air passes over the cold evaporator coil, and moisture condenses on the coil's surface — the same way water droplets form on a cold glass. This water drips into an internal collection tray.
How much water your unit produces depends on two things: the room's humidity level and the unit's cooling capacity.
| Relative Humidity | Condensate Production (10K BTU unit) | Drain Frequency (auto-evap) |
|---|---|---|
| 20%–30% (arid) | 0.3–0.8 pints/hour | Never |
| 30%–45% (moderate) | 0.8–1.5 pints/hour | Rarely (weekly or never) |
| 45%–60% (humid) | 1.5–2.5 pints/hour | Occasionally (every 1–3 days) |
| 60%–75% (very humid) | 2.5–3.5 pints/hour | Frequently (every 4–8 hours) |
| 75%+ (tropical) | 3.5–5+ pints/hour | Very frequently (every 2–4 hours) |
The Three Drainage Methods
Method 1: Auto-Evaporative (Most Common in 2026)
Most modern portable ACs spray or wick collected condensate onto the hot condenser coil. The water evaporates from the heat and exits through the exhaust hose as water vapor. You never see or touch the water.
How to tell if your unit has it: Check the manual for "auto-evaporation," "self-evaporative," or "no-bucket" technology. If the unit has no visible water tank or the tank is very small (under 1 quart), it likely auto-evaporates.
When it fails: In very high humidity (above 60%–65% RH), the auto-evaporative system can't keep up. The condenser coil can only evaporate so much water. Excess condensate fills the internal tray, triggering the "FL" (full) alarm and shutting off the compressor.
If your auto-evaporative unit triggers the "FL" alarm frequently, your humidity is too high for auto-evaporation alone. Set up a continuous gravity drain (Method 3) to handle the overflow. This is common in Houston, Miami, New Orleans, and similar climates.
Method 2: Manual Draining
Older units and some budget models collect condensate in a removable tank. When the tank fills, the unit shuts off and displays "FL" or "P1." You pull out the tank, dump the water, and replace it.
Step-by-step:
- Turn off the unit and unplug it.
- Place a shallow pan or towel under the drain area (usually the bottom-rear of the unit).
- Remove the drain plug or pull out the water tank.
- Empty the water into a sink, toilet, or bucket.
- Replace the plug/tank firmly.
- Plug in and restart the unit.
Tank sizes typically range from 0.5 to 1.5 gallons. At 3 pints/hour in a humid climate, a 1-gallon tank fills in about 2.5 hours. This is why continuous draining is recommended for humid areas.
Method 3: Continuous Gravity Drain (Best for Humid Climates)
Most portable ACs have a rear drain port with a threaded cap. Connecting a garden hose or drain hose to this port allows water to flow continuously into a floor drain, bucket, or sump.
What you need:
- 5/8" garden hose or the drain hose included with your unit
- Hose adapter (if not included) — typically a standard garden hose fitting
- Floor drain, bucket, or condensate pump within reach
Step-by-step:
- Locate the drain port on the back/bottom of the unit. It's usually a threaded fitting with a rubber cap.
- Remove the rubber cap.
- Thread the drain hose onto the port. Hand-tighten plus a quarter turn.
- Route the hose to a floor drain, bucket, or condensate pump. The hose must slope downward continuously — gravity is doing all the work.
- Secure the hose so it can't fall out of the drain or bucket.
- Check the connection daily for the first week to ensure no leaks.
The hose must slope downward from the unit to the drain. If any section of the hose sits higher than the drain port, water pools in the low spots and the unit's internal tray can still fill up. A 1/4" per foot slope is sufficient.
If you don't have a floor drain nearby: Use a condensate pump ($40–$80). These small pumps sit next to the AC and automatically pump collected water through a thin tube to a drain, window, or even up and over to a kitchen/bathroom sink. They're commonly used with dehumidifiers and work perfectly with portable ACs.
Drain Frequency by Climate
| Location | Avg. Summer Humidity | Auto-Evap Sufficient? | Manual Drain Frequency | Recommended Setup |
|---|---|---|---|---|
| Phoenix, AZ | 15%–25% | Yes — always | Never | Auto-evap only |
| Denver, CO | 25%–35% | Yes — always | Never | Auto-evap only |
| Los Angeles, CA | 30%–50% | Usually | Monthly (rare) | Auto-evap only |
| Seattle, WA | 40%–55% | Usually | Occasionally | Auto-evap + bucket backup |
| Chicago, IL | 50%–65% | Sometimes | Every 1–2 days | Gravity drain recommended |
| Atlanta, GA | 60%–75% | No | Every 4–8 hours | Gravity drain essential |
| Houston, TX | 65%–80% | No | Every 2–6 hours | Gravity drain essential |
| Miami, FL | 70%–85% | No | Every 2–4 hours | Gravity drain + pump essential |
What Happens If You Don't Drain
When the internal tray fills, the unit's float switch triggers a safety shutoff. The compressor stops, and the unit displays an error code ("FL," "P1," "E5," or similar, depending on the brand). The fan may continue running but no cooling happens.
This is a safety feature — not a malfunction. Without the shutoff, water would overflow from the tray onto your floor. The unit resumes normal operation once you drain the tank.
If the unit shuts off repeatedly every few hours, it's a signal that your climate's humidity exceeds the auto-evaporative system's capacity. Set up continuous gravity draining.
Maintenance and Cleaning
Monthly: Clean the Drain Tray
Even with auto-evaporation, the internal tray accumulates mineral deposits, dust, and potential mold/mildew over time. Once a month during active use, drain the unit manually and pour a cup of white vinegar or a 10% bleach solution through the drain port. Let it sit for 15 minutes, then drain.
Seasonal: End-of-Season Deep Clean
Before storing the unit for winter, drain all water completely by tilting the unit gently over a pan or towel, run the fan-only mode for 2–4 hours to dry out the internal components, clean the drain tray with vinegar, clean or replace the air filter, and store the unit upright in a dry location.
Mold risk. Standing water in a portable AC's tray is a mold breeding ground. If you notice musty odors from the unit, the tray needs cleaning. A bleach/vinegar flush followed by a fan-dry cycle usually resolves it. Never store the unit with water in the tray.
Example 1: Auto-Evap Success in Colorado Andrea in Denver runs her 10,000 DOE BTU Midea portable AC from June through August. In Denver's 25%–35% humidity, the auto-evaporative system handles everything. She's never had to manually drain the unit in 3 years of use. Her only maintenance: cleaning the filter every 2 weeks and the drain tray once at season end.
Example 2: Gravity Drain in New Orleans Marcus runs a portable AC in his New Orleans apartment bedroom. At 75%+ humidity, the auto-evaporative system fails within 3 hours, triggering the FL alarm at 2 AM. He connected a $12 garden hose from the rear drain port to a 5-gallon bucket by the bed. The bucket fills about every 16 hours — he dumps it each morning and evening. Problem solved for $12.
Example 3: Condensate Pump Solution Sarah's portable AC is in a converted office with no floor drain within 15 feet. She bought a $65 Little Giant condensate pump and connected it to the AC's drain port. The pump automatically pushes water through a 1/4" tube that she routed along the baseboard to the bathroom sink — about 20 feet away. The pump runs silently and handles up to 1 gallon per hour. Zero manual draining needed.
Key Takeaways
- Most modern portable ACs auto-evaporate condensate through the exhaust hose — no draining needed in dry climates.
- In humid climates (above 60% RH), auto-evaporation can't keep up — you'll need manual draining or a continuous gravity drain.
- Set up a gravity drain hose if you're draining manually more than once per day.
- A condensate pump ($40–$80) is the best solution when no floor drain is nearby.
- Clean the drain tray monthly with vinegar to prevent mold and mineral buildup.
- End-of-season deep clean prevents mold during storage — drain all water and run fan-dry for 2–4 hours.
- The "FL" alarm is a safety feature, not a defect — it prevents overflow onto your floor.
- Never store the unit with standing water in the tray — mold will grow.
Frequently Asked Questions
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