Reading Customer Ductwork Reference

Why this matters

Ductwork is often the invisible cause of HVAC complaints - uneven temperatures, high bills, poor airflow. The tech who can read ductwork condition diagnoses systemic issues vs symptomatic ones. This is the field card.

Ductwork basics

Function:

• Distribute conditioned air through home
• Return air to equipment
• Quiet operation (when designed well)

Components:

• Plenum: large central distribution point
• Trunk lines: main supply / return runs
• Branches: feed individual registers
• Registers: supply outlets (grilles)
• Returns: return air openings
• Dampers: control airflow
• Insulation: thermal + sound

Ductwork materials

Sheet metal (galvanized):

• Most common new
• Durable
• Sealed at joints
• Can be insulated externally

Flexible duct (flex):

• Plastic-lined, insulated
• Easier to route
• More restrictive (airflow)
• Common for branch runs

Fiberboard / duct board:

• Older systems
• Inherent insulation
• Can deteriorate
• Harder to clean

Lined sheet metal:

• Acoustic insulation interior
• Quiet but harder to clean

Visible ductwork inspection

What to check when accessible:

Connections:

• Sealed (mastic, tape) = good
• Open seams = leaks
• "Duct tape" only = will fail (despite name)

Insulation:

• Intact = good
• Damaged / missing = thermal loss
• Wet = mold concern

Flex duct:

• Kinked = airflow restricted
• Sagging = airflow restricted
• Damaged outer cover = insulation issue

Sheet metal:

• Rusted = water exposure
• Damaged = airflow issue
• Loose hangers = sagging

Registers + returns:

• Clean
• Open / unobstructed
• Damper position
• Adequate size for room

Common ductwork problems

Leaky ductwork:

• 20-30% energy loss common
• Especially in unconditioned space
• Lost cooling / heating
• Sometimes drawing in attic / crawlspace air

Undersized ducts:

• Reduced airflow
• High velocity = noise
• Inadequate room conditioning

Oversized ducts:

• Low velocity
• Stratification
• Sometimes condensation

Imbalanced system:

• Some rooms get more
• Some get less
• Comfort complaints

Restrictive flex duct:

• Kinked, crushed, sagging
• Reduces airflow significantly
• Common cause of low CFM

Inadequate returns:

• Pressure imbalance
• Doors slammed
• Reduced efficiency

Symptoms of ductwork issues

Customer complaints:

"Some rooms hot, some cold":

• Imbalanced distribution
• Damper adjustment OR redesign

"AC works but house never cools enough":

• Could be ductwork
• Leaks losing capacity
• Restrictive ducts

"High utility bills":

• Could be ducts
• Test for leaks
• Insulation check

"Air doesn't come out of one register":

• Damper closed
• Duct disconnected
• Restrictive flex

"System runs constantly":

• Multiple causes; ducts could contribute
• Capacity vs distribution

"Whistling / noise from vents":

• High velocity
• Undersized opening
• Damper partly closed

Diagnostic approach

When customer reports comfort issue:

1. Confirm equipment operating correctly (not equipment issue)
2. Measure return + supply temps (verify proper system performance)
3. Check airflow at each register (some quantitative)
4. Inspect accessible ductwork
5. Identify likely culprit

Airflow measurement

Vane anemometer:

• Measures CFM at register
• Compare room-by-room
• Identify low-flow areas

Hot-wire anemometer:

• More sensitive
• Better for low-flow

Smoke pen:

• Visualize airflow direction
• Identify leaks
• Quick assessment

Static pressure:

• Measure across system
• High = restriction
• Low = leakage

Static pressure ranges

Total static:

• 0.5 inWC typical residential
• 0.8 inWC = high; investigate
• Over 1.0 = problem

Supply duct:

• 0.1-0.3 inWC typical
• Higher = restriction

Return duct:

• 0.1-0.2 inWC typical
• Higher = restriction

Equipment-specific specs.

Duct leakage testing

Duct blaster:

• Pressurize duct system
• Measure leakage CFM
• Identify problem areas

Tracer fog:

• Inject fog into system
• Look for visible escape
• Identifies leaks visually

Smoke pen at suspicious joints:

• Quick assessment
• Less precise than blaster

Common leak locations

Joints:

• Supply trunk connections
• Branch to register boots
• Equipment connections

Damper bypass:

• Adjustable dampers leaking around
• Closed dampers leaking

Insulation gaps:

• Where insulation interrupted
• Thermal but sometimes air

Old fiberboard:

• Deteriorates over time
• Joint failure

Cross-trade observations

HVAC tech: primary; understands system

Cleaner: notices register condition; airflow at vents

Carpet cleaner: notices accumulated dust around vents

Roofer: notices attic ducts; sometimes condition visible

Pest control: notices animal damage to ducts (common in attics)

Asbestos in old ductwork

Older ducts (pre-1980s):

• Some have asbestos wrap
• Don't disturb without proper precautions
• Refer to abatement contractor
• Don't sand / break

If suspect asbestos wrap: stop; consult; don't damage.

Ductwork in different spaces

Attic:

• Most-common location for leaks
• Hot in summer / cold in winter
• Inadequately insulated commonly
• Repair OR insulate

Crawlspace:

• Damp environment
• Insulation degrades
• Rodent damage possible
• Encapsulation helps

Basement:

• Conditioned space typically
• Less critical leakage
• More accessible

Within conditioned space:

• Leaks less impactful (still inside envelope)
• But still affects distribution

Duct sealing

Mastic sealant:

• Brush OR caulk gun application
• Permanent
• Most-effective sealing

Aerosol sealing (Aeroseal):

• System pressurized
• Aerosol particles seal leaks from inside
• Professional service
• Effective for many leaks

UL 181 foil tape:

• For specific applications
• Not "duct tape"
• Long-lasting on clean surfaces

When to recommend duct upgrade

Strong indicators:

• Significant leakage measured
• Customer complains of uneven comfort
• Equipment runs more than expected
• High utility bills

Marginal:

• Small symptoms
• Customer's budget tight
• Other priorities higher

Return air issues

Often-overlooked:

• Inadequate returns = pressure imbalance
• Doors slammed in homes with central return only
• Reduced air movement
• Equipment can't move enough air

Solutions:

• Add returns per room
• Door undercuts
• Transfer grilles

Insulation

R-value targets:

• R-6 minimum for ducts in unconditioned space
• R-8 better
• R-4 inadequate

Inspect:

• Cover material intact
• No gaps
• Properly secured

Repair:

• Repair damaged sections
• Add insulation if inadequate

Customer education

What customer needs to know:

• Ductwork matters
• Leaky ducts waste energy
• Sealed ducts improve comfort
• Maintenance helps

Maintenance:

• Change filters regularly
• Vacuum register grilles
• Watch for symptoms
• Annual professional inspection

References

• ACCA Manual D (Duct Design)
• ACCA Manual J (load calculations)
• SMACNA standards
• Manuall internal: Ductwork Sizing Reference, Duct Sealing Methods