Existing duct leakage
Seams, joints, boot connections and plenum takeoffs that leaked before the replacement leak the same amount afterward, now losing air the new equipment produces.
HVAC performance
New AC but the House Is Still Hot?
An HVAC replacement changes the equipment that produces conditioned air. In most residential replacements it does not change the distribution system that delivers it. The condenser, air handler, furnace or heat pump is new; the ducts above the ceiling are the same ducts as before.
That is not a criticism of the contractor. Replacing distribution is a much larger scope, it is often not what the homeowner asked for or budgeted, and in many homes the existing system is serviceable. But it does mean that a comfort complaint caused by the distribution system can survive a full equipment replacement intact.
If the specific symptom you had before the replacement is the same symptom you have after it, that pattern is worth taking seriously.
Reviewed by Duct Daddy
Written and reviewed by the Duct Daddy team, a duct leakage testing and duct sealing specialist serving Southeast Louisiana. This article is general guidance, not a diagnosis of your system.
What a new system does not automatically correct
Duct sizing carried over from the old system
New equipment often needs different airflow than what it replaced. Ductwork sized for the previous system may not carry it.
Crushed or kinked runs
Compressed flex duct above a ceiling is unaffected by anything happening at the equipment.
Disconnected branches
A run that came loose at a collar — sometimes years ago, sometimes during attic work — delivers into the attic regardless of what is producing the air.
Airflow imbalance between rooms
If the system was never balanced, or dampers were set for a different piece of equipment, room-to-room differences persist.
Inadequate return air
Undersized or leaky returns limit what any equipment can deliver, and new higher-airflow equipment can make an existing return shortfall more noticeable.
Building-envelope issues
Insulation and air leakage in the house itself were never part of the equipment scope.
When to call a licensed HVAC service technician
Duct Daddy specialises in duct leakage testing and duct sealing. We do not perform mechanical HVAC repair, refrigerant work or equipment replacement. Contact a qualified HVAC contractor if any of the following apply:
- The new system is under warranty and behaving abnormally — call the installing contractor first.
- You hear unusual noises, see icing, or the system short-cycles.
- Airflow at the equipment itself seems dramatically different from before.
What testing the duct system tells you
A duct leakage test measures the distribution system independently of the equipment. If the ducts test tight, the conversation belongs with your HVAC contractor and the new equipment. If they test leaky, you have found something the replacement did not address.
Duct leakage is one of the few items on this list that can be measured rather than estimated. A duct leakage test pressurises the duct system and quantifies how much air is escaping, so the duct system either is or is not part of your problem — and you have a number either way.
Duct Daddy works as a specialty third-party provider and is not trying to displace your HVAC contractor. In many cases the useful outcome is a measured duct report that the contractor can work from.
More detail on the process: how air duct sealing works and how leakage is measured and verified.
Have the duct system measured
Before anyone concludes the new equipment is the problem, it is worth knowing what the distribution system is doing.
Related guides
New AC or new ductwork?
A framework for telling equipment problems, duct problems, design problems and envelope problems apart.
AC runs all day
Long runtimes are not automatically a fault — here is how to tell the difference between working hard and losing air.
Weak airflow at the vents
Barely any air at a register — and how to tell restriction, leakage and physical damage apart.
Browse every guide in the comfort guide.
Find out what your duct system is actually doing.
Schedule a duct leakage evaluation and get measured numbers for your home — not a guess.