Every heating and cooling problem in a house eventually gets blamed on the equipment. Sometimes the equipment is fine. The air leaves the outdoor unit, travels through a network of metal and flex duct buried in the walls and the attic, and arrives in the bedrooms as a warm trickle because a joint has pulled apart somewhere you cannot see.
Up to 30 percent of heated or cooled air can be lost through duct leaks, and 20 to 30 percent of cooled air goes the same way. When that happens the system runs longer to compensate, the bill climbs, and the rooms furthest from the unit suffer first.
Should the ducts be repaired or replaced?
Start with the pattern of symptoms rather than the number of leaks. One or two rooms that are uncomfortable, a house that cannot hold its temperature, or a system that runs for hours without catching up are all symptoms of the same underlying problem: the air is not arriving where it should.
Then decide whether the problem is local or system wide. A single disconnected joint, a crushed run against a rafter and a flex duct that has pulled off a register are local, and local problems are repair jobs. Ducts that are undersized for the house, sagging in every run or disconnected in several places are system wide, and system wide problems are replacement jobs.
What actually goes wrong with ductwork
Six faults account for nearly every duct problem we see in Central Valley homes.
- Joints that have pulled apart. Sheet metal expands and contracts through the summer, and a joint made with tape alone or a screw that was not sealed will eventually open. This is the most common fault and usually the easiest to fix.
- Disconnected runs. Where a duct has come away from a register or a return, the air has somewhere else to go, often into an attic void. You may not hear it, but the rooms downstream will be starved.
- Crushed or flattened flex duct. Flexible duct run over framing, under a beam or where a storage platform has been built across it gets compressed. Crushed flex moves a fraction of the air it was designed to move.
- Missing or fallen insulation. Insulation on a duct in a hot attic is what keeps the air inside the duct at the temperature it left the unit. Strip it off and the air picks up heat on the way.
- Undersized ducts. A system that was oversized when it was installed needed big ducts. If the ducts were later replaced with something smaller, the air path can no longer carry the air the equipment produces.
- Blocked or dirty ducts. A long return run with a sharp bend, a collapsed filter rack or years of dust and debris inside the run will choke the airflow before it reaches the room.
How to tell a repair from a replacement
| What you are seeing | What it usually points to | Repair or replace |
|---|---|---|
| One room is always warm or always cold | A disconnected run, a blocked register or a crushed section | Repair |
| Air is weak at the end of the house | Undersized duct, or a run pinched somewhere | Replace that run |
| The attic is noticeably hotter than usual | Open or disconnected ductwork dumping air into the void | Repair, then seal |
| Every room is uneven, in every season | Undersized ductwork across the house | Replace |
| The system runs for hours and never catches up | Air lost through leaks and undersized runs | Usually replace |
| Visible damage to metal duct, rusted through | Corrosion, usually with a rodent or moisture history | Replace the affected run |
| Rooms cooled by a later addition are still uncomfortable | The extension was never on the original duct layout | New run, and a decision on the old system |
| Whistling, rumbling or rattling from the duct | Loose or undersized flex duct | Repair, or replace if the flex has perished |
What a duct camera inspection actually shows
A duct camera is a small camera on a flexible cable that goes through a vent or an access point and travels inside the run. It is the single most useful tool for this job, because it removes the guessing.
The technician can see a joint that has pulled open and the gap around it. They can see flex duct that has been crushed flat or split along its length. They can see where insulation has fallen away and where water has pooled. They can find the disconnected run and see how far back it comes loose. They can see rodent damage and nesting, which is worth knowing before anyone opens a wall. And they can see whether the duct in the wall is the same size as the duct in the attic, which is often where the story stops making sense.
What the camera cannot do is judge the condition of a run it cannot reach. That comes from the plan of the house, the equipment and the symptoms you have described. We will tell you what an inspection shows and what we recommend afterwards, and we put the whole job, inspection included, in writing before any work starts.
What each option involves
For a replacement project, ductwork is quoted as part of the same job rather than as a separate line you have to guess at. It covers new or rebuilt runs where the old layout is wrong, where the ducts are undersized, or where they are in poor enough condition that reusing them would be false economy. The scope follows the condition of the runs, so we look before we write.
For a standalone repair, the price depends on the fault, where the duct is and how much access there is. A joint in an attic is a quick job. A run buried in a finished wall with no access is not, and sometimes the sensible answer is to run a new short duct to a new register rather than chase the old one through the plasterboard. We quote the exact price in writing before anything is ordered, and provide free phone consultations for installation guidance.
| Situation | What is involved | What it affects |
|---|---|---|
| A few failed joints, accessible | Re-sealing or replacing short sections | Measured in hours, quoted before we start |
| One crushed or disconnected run | New section, re-hung, insulated and sealed | One run, not a whole system |
| Ductwork upgraded during a system replacement | New runs, resized, insulated and connected to the new unit | Adds ductwork scope to the project, decided once the runs have been inspected |
| Ducts undersized or damaged throughout | A new duct layout designed for the equipment | Quoted as part of the replacement project |
| Undersized system on undersized ducts | New equipment sized to the air path, or a new air path | Decided with a load calculation |
Five questions to ask before you decide
- Have the ducts been inspected properly, or are we guessing? Ask whether a camera has been used, and ask to see what it found.
- Is the fix local or is it the whole system? A local repair is a line item. A whole system is a different conversation and a different price.
- What happens to the equipment if we only repair? A repaired duct run lets the existing system work properly, which is usually the cheapest way to get the performance back.
- Is the system itself the right size? If the ducts cannot carry the air, a bigger outdoor unit makes the problem worse, not better.
- What is the total, in writing? Including any ductwork, and including whether the work is inside a wall or in the attic.
When to stop and call a licensed technician
Some duct checks are safe to make yourself. Anything beyond that is a job for a licensed technician, and some of it is a job for a technician today.
- You can open a register and look up into the duct. You cannot reach in and pull out a section of it.
- You hear a whistling or rumbling noise that changes when you change the fan speed, and you cannot find a loose grille or a blocked return.
- You can see daylight, insulation falling out or a gap where two pieces of duct should meet. Cover it with foil HVAC tape if it is accessible and safe, and do not leave it like that.
- You find evidence of rodents, insects or nesting inside the ductwork. That needs to be dealt with before the duct is sealed back up.
- You find standing water, a wet ceiling or a stained wall around a register. Water and a running system is a problem that gets worse every hour it is left.
- Any work that involves opening a wall, a ceiling or an electrical panel. Both need a licensed trade.
RB HVAC Inc. is a licensed HVAC contractor based in Stockton, licensed in California under number 1094161. We have served the Central Valley since 2010, we work across Stockton, Sacramento, Modesto and surrounding communities, and we are rated 4.9 on Google across 215+ Google reviews. We provide transparent diagnostics and upfront written pricing before any work starts, with free phone guidance for installation planning.
