You can buy the most efficient air conditioner made and still have an uncomfortable, expensive house if the ductwork is leaking. The equipment gets all the attention. The duct system is what actually delivers the air, and in the Lowcountry it takes a beating.
Most of the duct problems we find are fixable without replacing anything. Sealed joints, re-supported runs, corrected insulation and a repaired vapor barrier will transform how a house feels — usually for a fraction of what people assume.
What duct leakage costs you
Every leak in a supply duct is conditioned air you paid to cool, dumped into a crawlspace or attic. Duct leakage commonly wastes a large share of a system’s output, which means a meaningful chunk of your power bill is air-conditioning the space under your floor.
Leaks on the return side are worse in this climate, because a return leak does not just lose air — it pulls air in. In a vented crawlspace during a Charleston summer, that means hot, humid, unfiltered air entering your system upstream of the filter and coil. Your equipment now has to remove moisture it never should have seen, and your house still feels damp.
That is the mechanism behind one of the most common complaints we get: the house is cool but clammy. Before assuming you need a dehumidifier, it is worth checking whether the ducts are drinking crawlspace air.
What we find under Lowcountry houses
Disconnected joints
Flex duct is often attached to a metal collar with a zip tie and tape. Tape dries out. In older homes around downtown Charleston, West Ashley and James Island, we regularly crawl under a house and find a supply branch lying on the ground, completely off its collar, blowing cold air into the dirt. The homeowner has been told for two summers that the back bedroom just runs warm.
Crushed and kinked flex duct
Flex is easy to install and easy to install badly. Kinked around a pier, crushed under a plumbing run, or draped in long sagging loops between supports, it strangles airflow. A duct with a sharp bend can lose most of what it should be delivering.
Damp and failed insulation
Duct insulation in a humid crawlspace only works if the outer vapor barrier is intact. Once it tears, moist air reaches the cold duct surface, condenses, and the insulation soaks. Wet insulation insulates nothing, drips onto the ground, and creates exactly the conditions for growth and musty odors. This gets much worse after storm flooding.
Poor design
Some systems were never right. Undersized trunks, too many branches off one run, no return path from bedrooms with the doors closed, or a room added years later fed by a long skinny branch off the far end. These are the rooms that never get comfortable no matter what the thermostat says.
How we find the leaks
We do not guess. A repair visit starts with measurement and inspection: static pressure readings to see whether the system is fighting restriction, airflow at individual registers to find the underperforming rooms, and a physical crawl through the crawlspace or attic with a light and camera.
Where it is useful, we pressure test the duct system to quantify how much is leaking rather than describing it in adjectives. You get photographs of what we found — the actual disconnected boot under your house, not a stock image.
How we seal and repair
- Mastic on every joint. Brushed-on duct mastic, mechanically fastened, is the durable fix. It stays flexible and it does not let go in five years the way tape does.
- Reconnection with proper mechanical fastening. Collars, straps and clamps, not a zip tie and hope.
- Removing kinks and re-supporting runs. Correct hanger spacing, gentle radius bends, no sags collecting water.
- Replacing damaged sections. A crushed or waterlogged section gets replaced. Sealing a ruined duct is not a repair.
- Insulation and vapor barrier. In our crawlspaces this is not optional. Insulation with an intact, sealed outer vapor barrier is what keeps the duct from sweating in July.
- Sealing boots at the floor. The connection between duct and floor register is a frequent and easily missed leak point.
After the work, we re-measure. Static pressure and register airflow should both move in the right direction, and you should be able to feel it at the vents in the rooms that were struggling.
What you should notice afterward
Rooms that used to run three or four degrees warm coming into line. The system reaching setpoint and holding it instead of running all afternoon. Less dust, because the return has stopped pulling from under the house. And in most cases a genuine reduction in dampness, since crawlspace moisture is no longer being fed directly into your air.
Duct sealing also protects equipment. A system fighting high static pressure works harder than it was designed to, and that shortens the life of the blower and compressor. If you are already considering new equipment, fix the ducts first — otherwise the new system inherits the same problem, and maintenance will not make up the difference.
Repair or replace the ductwork?
If the duct is intact and correctly sized but leaking at joints, repair is straightforward and worth every dollar. If it is undersized, badly designed, crushed in multiple places, or the insulation has been wet for years, we will tell you honestly that replacement is the better investment.
Cost depends on how much duct there is, crawlspace access and clearance, how many repairs are needed and whether insulation has to be redone. You get a written itemized quote after we have been under the house. Our technicians are paid no commission, and financing is available subject to approved credit.
If a room in your house has never been comfortable, the answer is probably under the floor. Call or text 843-609-5740, or book an inspection online.
Cleaning the ducts is a separate job from repairing them. If the ducts are sound but the air is not, see air duct cleaning under indoor air quality.
