Ductwork
The supply and return duct network that carries air between the air handler and the rooms it serves. Undersized returns, crushed flexible duct, and leaking joints all reduce delivered capacity without producing an equipment fault code.
Also called ducts, duct system
What is ductwork?
Ductwork is the network of supply and return ducts carrying air between the air handler and the rooms. It decides how much of the equipment's capacity actually reaches each room.
Ductwork: how it works
One blower pushes air through the supply branches and pulls it back through the returns, and every bend, reduction, and length of flexible duct adds resistance. Air also escapes through unsealed joints, and duct in an unconditioned loft or crawl space loses heat through its walls, so the air that reaches a register can be both less and less conditioned than what left the coil.
Where you meet the term
- In a room that never reaches the set temperature while the equipment measures normally.
- In a static pressure reading, because the ducts are what that pressure is measuring.
- In an energy assessment, where duct leakage in an unconditioned space is treated as a direct loss.
How to check it
- Look at any accessible flexible duct. Compressed, kinked, or sharply bent flexible duct restricts air noticeably, and an exposed loft run can be inspected without tools. Owner check
- Feel for air at joints in an unconditioned space. Air escaping at a joint in a loft is air the room paid for. Tape that has aged and released is a recognised failure. Owner check
- Measure airflow at the registers. A flow hood at each register shows how the total is distributed, which is what turns a comfort complaint into a measured design problem. Technician
Ductwork: what it is not
- Duct tape is not the product for sealing ducts. Mastic and foil tapes rated for the purpose are, and ordinary cloth tape releases as it ages.
- A duct problem produces no fault code. The equipment reports what it measures, and it does not measure the duct network.
Ductwork questions
Why is one room always warmer than the rest?
One blower serves the whole network, so branch length, duct size, leakage, and the return path decide the share each room gets. Measuring airflow at the register is what distinguishes a distribution problem from an equipment one.
Does duct leakage really matter?
Air lost in an unconditioned loft or crawl space is conditioned air the equipment paid to produce, and it also unbalances the pressure between supply and return. It is one of the losses that never shows up as a fault.
Is flexible duct worse than rigid?
It is not worse when installed straight, supported, and at full stretch. It becomes worse when it sags, kinks, or is left compressed, because the inner liner ripples and adds resistance.
Where this definition comes from
Written from standards body publication material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- ASHRAE TerminologyIndustry reference definitions for heating, ventilation, air conditioning, and refrigeration vocabulary.