Dripping near the indoor unit only in cooling mode
Clear water forms under or beside the air handler after the system has been cooling for a while.
Start here: Start with the condensate pan and drain line.
Heat Pump Leak Troubleshooting
Heat Pump Drips in Crawl Space
Direct answer: If your heat pump drips in the crawl space, the most common cause is condensate not draining where it should. Start by figuring out whether the water is coming from the air handler drain line, a secondary pan, a frozen indoor coil thawing out, or cold ductwork sweating in humid air.
Most likely: Most often, this is a clogged condensate drain or a sagging drain line near the indoor unit in the crawl space.
A little water in cooling season can be normal inside the drain system. Water dripping onto the crawl space floor, insulation, or framing is not. Reality check: a heat pump can make a surprising amount of condensate on humid days. Common wrong move: pouring harsh chemicals into the drain before you confirm where the water is actually coming from.
Don’t start with: Do not start by replacing electrical parts or opening sealed refrigerant components. Water around HVAC equipment can also mean a frozen coil or airflow problem, and that changes the repair path.
If the water is clear and shows up only when cooling runs,check the condensate drain and pan first.
If you see ice, weak airflow, or the unit has been running nonstop,treat it like a frozen-coil problem and stop there before guessing at parts.
Last reviewed: 2026-04-05
What the crawl space leak looks like
Water starts after the unit ices up or airflow gets weak
You may see frost or ice on refrigerant lines, then a lot of water later as it melts.
Start here: Start with the filter, vents, and indoor coil freeze clues.
Water is on duct insulation or hanging from metal duct seams
The air handler itself may be dry, but nearby ducts are wet or dripping.
Start here: Start with duct sweating and crawl space humidity checks.
Water shows up in a pan under the unit
A secondary pan has standing water or the overflow outlet is dripping.
Start here: Start with a blocked primary drain or poor unit pitch.
Most likely causes
1. Clogged heat pump condensate drain line
This is the most common reason clear water ends up in the crawl space during cooling. Algae, sludge, or debris backs water up until it spills from the pan or fittings.
Quick check: Look for standing water in the primary drain pan or a slow drip from an overflow outlet while the system is running.
2. Heat pump condensate drain line sagging, disconnected, or pitched wrong
In crawl spaces, drain tubing gets bumped, sags between supports, or pulls loose at a fitting. Water then drips before it reaches the proper discharge point.
Quick check: Follow the drain line by eye and look for low spots, loose joints, or a section that drains uphill.
3. Indoor heat pump evaporator coil freezing and then thawing
A dirty filter, blocked airflow, or a refrigerant problem can freeze the indoor coil. When the ice melts, the pan can overflow or water can miss the pan entirely.
Quick check: Check for weak airflow, ice on the refrigerant line, or frost around the indoor coil cabinet.
4. Cold crawl space ductwork sweating
If the crawl space is humid and duct insulation is damaged or missing, condensation can form on the outside of ducts and drip like a leak.
Quick check: Touch the outside of the duct insulation. If it feels wet over a broad area while the air handler cabinet stays mostly dry, sweating is more likely than a drain leak.
Step-by-step fix
Step 1: Pin down exactly where the water starts
You do not want to treat a drain clog when the real problem is sweating ductwork or a frozen coil. The source usually shows itself with a careful look while the system is off and then again after it runs.
- Turn the thermostat to Off before opening any access panel or reaching near the indoor unit.
- Use a flashlight to inspect the floor, framing, insulation, drain line, pan area, and nearby ducts.
- Look for the highest wet point, not just the biggest puddle.
- Check whether the water is coming from the drain connection, the edge of the air handler, a secondary pan, or the outside of insulated ductwork.
- If the unit has been cooling, wait a few minutes and see whether dripping resumes from one exact spot after you restore operation.
Next move: If you can trace the water to the drain line or pan area, move to the drain checks next. If the whole area is wet and you cannot tell whether it is a drain leak, coil freeze, or duct sweating, stop before opening more of the system.
What to conclude: A clear source saves time. Drain leaks, freeze-ups, and sweating ducts can all look similar from the crawl space floor.
Stop if:
- You see exposed wiring getting wet.
- The cabinet insulation is saturated and sagging into electrical sections.
- You find heavy mold growth, rotted framing, or standing water deep enough to make footing unsafe.
Step 2: Check the condensate pan and drain line first
This is the safest and most common fix path. Most crawl space dripping during cooling is just water not leaving through the primary drain the way it should.
- Shut power to the indoor unit at the service switch or breaker if you need to remove an access panel.
- Inspect the primary drain pan for standing water, rust trails, slime, or debris.
- Follow the heat pump condensate drain line from the pan connection to its discharge point if accessible.
- Look for kinks, sags, loose slip joints, cracked tubing, or a section that has come apart.
- If there is a cleanout tee and you can reach it safely, clear the line with gentle suction from the outlet end or flush with plain water only after confirming the line is intact and routed correctly.
- Re-secure a loose drain line so it slopes steadily toward the outlet without low spots that trap water.
Next move: If water begins draining normally and no new dripping shows up around the unit, you likely found the problem. If the pan refills quickly, water misses the pan, or the line is clear but dripping continues, move on to freeze and airflow checks.
What to conclude: A backed-up or badly pitched drain is the leading cause. If the drain is open and the leak continues, the system may be making more water than the pan can handle because of icing or another fault.
Stop if:
- The drain fitting at the air handler is cracked inside the cabinet and not easy to access safely.
- The pan is badly rusted through or the cabinet is leaking from an internal seam.
- You cannot clear the line without forcing pressure back into the unit.
Step 3: Rule out a frozen indoor coil before you run it longer
A frozen coil can dump a lot of water into a crawl space after it thaws, and continuing to run the system can make the mess worse. This is the lookalike branch that gets missed most often.
- Check the air filter and replace it if it is visibly dirty or collapsed.
- Make sure supply registers and return grilles are open and not blocked by storage, rugs, or furniture.
- Look for ice or heavy frost on the larger insulated refrigerant line near the indoor unit.
- Notice whether airflow at the vents is weaker than usual or the system has been running for long stretches without satisfying the thermostat.
- If you find ice, turn cooling Off and switch the fan to On to help thaw the coil, then wait for the ice to melt completely before judging the leak again.
Next move: If the leak stops after thawing and restoring airflow with a clean filter and open vents, poor airflow was likely the trigger. If the coil freezes again, airflow is still weak, or the system is not cooling properly, the problem is beyond a simple drain issue.
Stop if:
- Ice returns after a clean filter and open vents.
- You hear the blower struggling, squealing, or not moving much air.
- You suspect refrigerant loss or see oily residue around refrigerant tubing.
Step 4: Check for duct sweating and crawl space moisture problems
If the air handler and drain are mostly dry but the ducts are wet, you are chasing condensation on the outside of the system, not a drain failure. That repair path is different.
- Inspect nearby supply ducts for torn insulation, bare metal spots, open seams, or crushed sections.
- Feel whether moisture is spread across the outside of the duct insulation instead of concentrated at one drain point.
- Look for signs of high crawl space humidity such as damp soil, wet joists, or condensation on other cool surfaces.
- Reattach loose duct insulation jacket sections if they have simply come apart and can be closed without compressing the insulation.
- If the crawl space is very humid, focus on moisture control and insulation repair rather than the condensate line.
Next move: If drying and re-securing damaged insulation stops the dripping, the water was condensation on the duct exterior. If the ducts are dry but the unit area still leaks, go back to the air handler and treat it as a drain or coil issue.
Stop if:
- Duct insulation is moldy, falling apart, or contaminated over a large area.
- You find major crawl space moisture intrusion from outside water or plumbing.
- The duct jacket damage is extensive enough that large sections need replacement.
Step 5: Stabilize the area and decide whether this is still DIY
By this point you should know whether you fixed a simple drain issue or whether the leak is tied to icing, damaged internal parts, or bigger moisture problems. The right next move matters more than guessing.
- If you corrected a clear drain line problem, run the system for one full cooling cycle and watch the pan, drain outlet, and crawl space floor.
- If the leak was caused by a dirty filter or blocked airflow, install the correct filter, keep vents open, and monitor for any return of ice or water.
- If you found a cracked pan, repeat freeze-ups, blower trouble, or signs of refrigerant trouble, leave the system off and schedule HVAC service.
- Dry wet insulation and nearby framing as soon as practical so a small HVAC leak does not turn into a crawl space moisture problem.
- If water damage is already spreading, use temporary containment under the leak point until the repair is completed.
A good result: If the drain carries water properly and the crawl space stays dry through several cooling cycles, the repair path is complete.
If not: If water returns, especially with icing, weak airflow, or cabinet leaks, stop DIY and have the system serviced.
What to conclude: Simple drain issues are reasonable homeowner fixes. Repeat leaking usually means the system has another fault feeding the water problem.
Stop if:
- Water returns after you already cleared and re-pitched the drain line.
- The indoor unit leaks from inside the cabinet rather than the drain connection.
- Any repair would require live electrical testing, blower disassembly, or refrigerant work.
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FAQ
Is it normal for a heat pump to drip water in a crawl space?
It is normal for a heat pump to make condensate in cooling mode, but that water should leave through the drain system. It is not normal for it to drip onto the crawl space floor, framing, or insulation.
Why does my heat pump leak only when the AC is running?
That usually points to condensate from the indoor coil. The most common causes are a clogged drain line, a pan overflow, or a frozen coil thawing after restricted airflow.
Can a dirty filter make a heat pump leak water?
Yes. A badly clogged heat pump air filter can choke airflow enough to freeze the indoor coil. When that ice melts, the pan can overflow or water can drip where it should not.
Why are my crawl space ducts dripping if the air handler is dry?
That is often duct sweating, not a drain leak. Humid crawl space air condenses on cold duct surfaces when insulation is damaged, missing, or poorly sealed.
Should I keep running the heat pump if it is leaking in the crawl space?
Only if you confirmed it was a simple drain issue and the water is now draining correctly. If you see ice, weak airflow, wet electrical parts, or repeated leaking, shut it off and get it serviced.