Troubleshooting center
HVAC Airflow & Home Comfort Troubleshooting
Start with the symptom you actually notice — a bedroom that never cools, a register that barely blows, a system that runs all afternoon, a house that stays clammy — and work toward what is really causing it.
Duct leakage is one possible cause among many. These guides say plainly when the evidence points somewhere else, including when the right next call is a licensed HVAC contractor rather than us.
Hot & Cold Rooms
One room never keeps up, upstairs runs hotter, or temperatures swing from room to room.
One room stays hot
A single room that never keeps up with the rest of the house, and how to find out why.
Read the answerUpstairs runs hot
Stack effect, attic heat gain and duct location all push upstairs temperatures higher than downstairs.
Read the answerBedroom stays hot with AC running
The system is running and cooling elsewhere, but this bedroom still doesn't cool down.
Read the answerRoom heats up when door shuts
A room that cools fine with the door open but heats up as soon as it's closed points to a pressure problem.
Read the answerOne room stays cold
A room that overcools while others struggle usually points to oversupply, sizing or thermostat placement.
Read the answerBig swings room to room
When several rooms disagree at once, the cause is usually system-wide balance, not any single room.
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Weak Airflow
Registers that barely blow, rooms at the end of a run, or airflow that dropped off.
Weak airflow at every vent
Every register in the house blowing softer than it should, and what that pattern usually points to.
Read the answerOne vent, weak airflow
A single register that barely moves air while the rest of the house seems fine — usually a branch-level problem.
Read the answerWeak airflow at the end of the run
The room farthest from the equipment consistently gets less air — the reasons distance alone can, and can't, explain.
Read the answerAirflow varies room to room
Some vents blow strong, others barely move air — what an uneven pattern across the house usually means.
Read the answerAC running, little airflow
The system is on and audibly working, but registers barely move air — a pattern that usually points inside the equipment.
Read the answerStill weak after a new filter
A fresh filter didn't fix it — what to check once the most obvious cause has already been ruled out.
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Problems After AC Replacement
New equipment, same complaints — what a replacement fixes and what it leaves untouched.
All 6 problems after ac replacement guides
Still hot after a new AC
New equipment doesn't change the ducts, the load, or the envelope — and any of those can leave a house hot.
Read the answerOne room still hot with a new AC
A single room's shortfall usually traces to the duct branch feeding it, not the equipment supplying the whole system.
Read the answerPoor airflow after replacement
New equipment can only push as much air as the duct system will pass — a restriction upstream limits everything downstream.
Read the answerNew AC runs constantly
Long runtime after a replacement can be normal variable-speed behaviour, or a sign the equipment is fighting a load or duct problem.
Read the answerHigh bill after new AC
Efficiency ratings describe the equipment, not what actually reaches the rooms — losses elsewhere in the system erase the expected savings.
Read the answerStill humid after new AC
Cooling and dehumidifying are related but distinct jobs — a new unit can lower temperature without controlling humidity if airflow or runtime isn't right.
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Duct Leakage
How to tell whether conditioned air is escaping before it reaches your rooms.
Telling if ducts are leaking
The visual and comfort clues that suggest leakage, and why only a test confirms it.
Read the answerSigns of leaky ductwork
The pattern of symptoms — comfort, bills, and physical clues — that together suggest duct leakage.
Read the answerDuct leaks and hot rooms
How a leak in the run serving one room can leave it warmer than the rest of the house.
Read the answerDuct leaks and weak airflow
Why leakage more often reduces delivered air than register velocity, and when it does neither.
Read the answerAir escaping into the attic
How to tell whether ductwork is dumping conditioned air into an unconditioned attic.
Read the answerWhat causes attic duct leakage
The specific failure points that develop in attic ductwork over time and at installation.
Read the answer
High Energy Bills & Long Runtime
Systems that run all day, never satisfy, or cost more than they used to.
All 5 high energy bills & long runtime guides
Runs all day, still not cool
Continuous runtime without a satisfied thermostat means capacity or delivery is falling short of the heat load.
Read the answerRuntime has crept up
A gradual increase in runtime usually points to a gradual loss somewhere — capacity, delivery, or load — not a single sudden failure.
Read the answerHigh bill despite new AC
New equipment fixes what's inside the cabinet — it does not automatically fix distribution, sizing, or envelope issues elsewhere in the house.
Read the answerAC never cycles off
A system that never shuts off is either matched to a heavy load and doing its job, or is losing capacity or air faster than it can produce it.
Read the answerDo leaky ducts raise bills?
Yes, leaking supply and return ducts can raise energy use — but the size of the effect depends on where the leaks are and how the ducts are routed.
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Humidity & Condensation
Clammy houses, sweating ducts and registers, musty smells — and what drives them.
All 5 humidity & condensation guides
House Humid With AC Running
Cooling and dehumidifying are not the same job, and a system can do one without the other.
Read the answerDucts Sweating in the Attic
Condensation on ductwork means a cold surface is meeting warm, humid air — usually an insulation or leakage issue.
Read the answerCondensation Around Vents
Sweating registers usually mean warm, humid room air is meeting a surface cooled well below the room's dew point.
Read the answerCeiling Vent Sweating
A sweating ceiling register risks staining or water damage and usually traces back to insulation, a boot gap, or nearby duct leakage.
Read the answerMusty Smell From Vents
A musty odour from vents usually points to moisture somewhere in the system and is worth having assessed rather than masked.
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Return-Air & Pressure Problems
Doors that pull shut, starved returns and rooms that pressurise when the AC runs.
All 4 return-air & pressure problems guides
Bedroom without a return
Most bedrooms rely on a central return elsewhere in the house — whether that works depends on the door and the gap beneath it.
Read the answerDoor hard to close with AC on
A door that resists closing, swings on its own, or whistles at the edges is a room pressurising because return air has nowhere to go.
Read the answerNot enough return air
Weak airflow across the whole house, doors that resist closing, and a struggling system can all point to a starved return side.
Read the answerReturn-air problem signs
From doors that won't stay shut to a system that runs constantly, here is how return-air trouble shows up around the house.
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Duct Design & Sizing
Whether the duct system was ever sized for the air the equipment is trying to move.
All 5 duct design & sizing guides
Undersized ducts
Trunks and branches too small for the equipment's airflow will restrict delivery no matter how tight they are.
Read the answerOversized ducts
Ducts sized larger than the airflow they carry can lose velocity, throw and even comfort — bigger is not automatically better.
Read the answerDuctwork sizing check
Correct sizing is confirmed with Manual J/S/D calculations and static-pressure measurement — not by eye.
Read the answerNew AC, old ducts
Not automatically — but the existing duct system needs to be evaluated against the new equipment's airflow, not just reused.
Read the answerExisting ducts vs. new AC
Handling capacity comes down to measured static pressure and physical condition, not the ductwork's age alone.
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Testing & Diagnosis
What is actually measured, how duct leakage testing works, and what the numbers mean.
All 3 testing & diagnosis guides
How Is Duct Leakage Tested?
The equipment and steps behind a duct pressurisation test, and what each reading measures.
Read the answerWhat Is a Duct Leakage Test?
What the test actually measures, how it differs from a general inspection, and what it does not tell you.
Read the answerWhat a Duct Leakage Number Means
How to read a CFM25 result — relative to what, judged against what, and what it can't tell you alone.
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Duct Sealing vs. Replacement
When sealing is the right call, when replacement is, and how to tell the difference.
All 4 duct sealing vs. replacement guides
Is Duct Sealing Worth It?
What sealing can and cannot fix, and how to know if your duct system is a good candidate.
Read the answerSealing vs. Replacement
How to tell whether your duct system needs sealing, replacement, or neither.
Read the answerAerosol vs. Manual Sealing
How the two sealing methods work, what each is good at, and where each falls short.
Read the answerWhen to Replace, Not Seal
The specific conditions that make sealing the wrong choice and replacement the honest one.
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Ready to stop guessing?
Read how duct sealing works, see the measure, seal and verify process, or browse the longer-form comfort guides.
Find out what your duct system is actually doing.
Schedule a duct leakage evaluation and get measured numbers for your home — not a guess.