Direct answer: ERV duct condensation usually comes from warm humid air hitting a cold duct surface, not from a failed part inside the ERV. Start by figuring out whether the moisture is on exterior duct insulation, at a loose joint, or actually coming from the unit cabinet or drain.
Most likely: The most common causes are missing or damaged duct insulation, air leaks at duct seams, restricted airflow from dirty ERV filters, or a condensate drain issue if the unit is producing water normally but not shedding it where it should.
When an ERV duct sweats, the fix is usually about temperature difference, humidity, and airflow. In the field, you want to separate a cold duct sweating in a humid space from a true leak first. Reality check: a little surface sweating in a hot humid attic or basement can turn into real water damage fast. Common wrong move: wrapping over wet insulation without fixing the air leak or moisture source underneath.
Don’t start with: Do not start by ordering an ERV motor or control board. Those are not the usual reason a duct is sweating.
The duct jacket feels damp or you see beads of water over several feet, usually in an attic, crawlspace, basement, or utility room.
Start here: This usually points to missing, thin, or damaged insulation, or indoor humidity that is too high for the duct surface temperature.
Drips form at a seam, collar, elbow, or connection near the unit while the rest of the duct looks dry.
Start here: Start with an air leak check. Cold air escaping at one joint can make that exact spot sweat heavily.
The duct may be wet near the unit, but the cabinet bottom, drain area, or inside pan area is also damp.
Start here: Treat this as a unit condensate or internal moisture issue first, not just a duct insulation problem.
The problem shows up during weather swings, then eases off when conditions change.
Start here: That pattern usually means the ERV is operating, but airflow balance, humidity load, or duct insulation margin is too close to the edge.
If the duct surface gets cold enough in a humid space, moisture forms on the outside just like a cold drink sweating on a table.
Quick check: Look for torn insulation jackets, bare metal, compressed insulation, or sections that feel much colder than the rest.
A small leak can dump cold air onto one spot and create heavy sweating right at a joint, takeoff, or elbow.
Quick check: Run the ERV and feel around seams for moving air. Staining, loose tape, or dark dust tracks often mark the leak.
Low airflow can make parts of the system run colder than normal and can also upset how moisture moves through the unit and ducts.
Quick check: Pull the ERV filters and inspect for heavy dust loading, matting, or obvious blockage at the core face if accessible.
If water is backing up in the unit, it can show up at nearby duct connections and look like duct condensation when it really started inside the cabinet.
Quick check: Check for standing water in the ERV, a slimy or kinked drain line, or water marks starting at the cabinet rather than mid-duct.
You need to know whether the moisture is forming on the outside of a cold duct, leaking from a seam, or coming from the ERV cabinet itself. That changes the fix completely.
Next move: If you clearly identify the starting point, you can stay on the right repair path instead of chasing the whole system. If everything is wet and you cannot tell where it begins, shut the unit back off and inspect again after the area dries more fully.
What to conclude: Mid-run sweating usually means insulation or room humidity. A single wet joint usually means an air leak. Water beginning at the cabinet points to an internal drain or setup issue.
Dirty filters and blocked airflow are common, safe to inspect, and often make condensation worse even when they are not the only cause.
Next move: If airflow improves and sweating drops noticeably over the next day, restricted airflow was at least part of the problem. If filters were clean and airflow sounds normal, move on to insulation and seam checks.
What to conclude: A dirty ERV filter is one of the few common homeowner-fix items on this symptom. If the unit still sweats after airflow is restored, the main issue is usually insulation, leakage, or condensate handling.
Most ERV duct condensation complaints come down to cold surfaces exposed to humid air or a small leak at one connection.
Next move: If you correct an obvious leak or insulation gap and the sweating stops at that exact spot, you found the main cause. If the duct is fully insulated and tight but still sweating broadly, the space humidity or ERV operating setup needs more attention.
If water is starting at the cabinet, fixing duct insulation alone will not solve it. The unit may be holding water or sending it the wrong way.
Next move: If the drain starts flowing and cabinet moisture stops returning, the nearby duct wetting was likely secondary to the drain issue. If water keeps collecting in the unit, or you see frost or freeze-thaw signs, it is time for service.
By this point you should know whether you are dealing with a basic maintenance issue, a duct insulation repair, or a unit problem that needs a pro.
A good result: If the duct stays dry through a normal run cycle and the surrounding insulation remains dry the next day, the repair path was successful.
If not: If sweating returns quickly, especially across multiple runs or only during weather extremes, you likely need airflow balancing, setup correction, or deeper unit service.
What to conclude: The only common buy-first item here is the ERV filter when it is visibly dirty or damaged. Most other fixes depend on what you found, and many cabinet-side moisture problems are service work.
Repair Riot may earn a commission from qualifying purchases, at no extra cost to you.
A little moisture can show up when conditions are extreme, but steady sweating or dripping is not something to ignore. If insulation gets wet or water starts staining nearby materials, the system needs attention.
Summer air is often warm and humid. If that air hits a cold duct surface, condensation forms fast, especially in basements, attics, and utility rooms with poor insulation or leaky seams.
Yes, it can contribute. Dirty ERV filters reduce airflow, which can make parts of the system run colder and can worsen moisture problems. It is not the only cause, but it is one of the first things worth checking.
Not until you know why it is wet. If the insulation underneath is soaked or a seam is leaking air, wrapping over it can trap moisture and make the problem worse. Dry it out, find the source, then repair or replace the affected insulation properly.
Call for service if water starts at the cabinet, the drain will not clear, the unit shows frost or ice, airflow seems off even with clean filters, or the condensation keeps coming back after basic insulation and seam fixes.