ACCA Manual J / D / S Engineering · Custom Sheet Metal · Airflow Balancing

Custom Sheet-Metal Ductwork & Airflow Redesign.

Q: Can you redesign the ductwork on our existing HVAC system regardless of brand?

Yes. Whether your home runs Mitsubishi, Lennox, Trane, Carrier, or another leading inverter or split platform, airflow physics are universal. We redesign plenums, return pathways, and supply trunks to match your equipment's exact blower curve and static pressure specification.

Even the highest-rated air conditioner or heat pump will struggle if it is connected to undersized, kinked builder flex duct and a choked return plenum. We solve hot upstairs bedrooms, noisy ceiling vents, and uneven room temperatures at the root—engineering custom galvanized sheet-metal plenums, square-to-round transitions, UL-181 mastic-sealed trunks, and linear slot diffuser plenums across Westlake Village, Thousand Oaks, Calabasas, Hidden Hills, Malibu, and Beverly Hills.

Schedule an Airflow & Duct Evaluation See Our Attic Craftsmanship

Manual DRoom-by-room CFM sizing

UL-181Mastic-sealed sheet metal

All BrandsCustom plenum retrofits

Custom fabricated sheet-metal supply and return plenums with plywood service walkway in attic

Above-Ceiling Sheet-Metal Craftsmanship

Hand-fabricated galvanized plenums, labeled branch takeoffs, manual balancing dampers, and full plywood service walkways.

Why Rooms Heat & Cool Unevenly

We Fix the Airflow Physics Most Contractors Ignore

Swapping an old outdoor box for a bigger unit without fixing restrictive attic ductwork only makes vents louder while leaving far bedrooms warm. Here is how we engineer quiet, balanced delivery.

Static Pressure Target ≤ 0.50" WC

Most builder duct systems choke blowers at 0.90"+ WC. We enlarge returns and transitions so variable-speed blowers breathe effortlessly.

Sheet-Metal Plenums Square-to-Round

Custom-fabricated galvanized supply and return plenums with triangulation break lines eliminate turbulent pressure drops at the coil.

Attic Heat Protection R-8 Insulated

UL-181 mastic-sealed seams and deep R-8 insulation prevent 55°F supply air from warming up inside a 135°F Conejo Valley attic.

Acoustic Delivery Linear Slots

Internally lined acoustic plenums keep face velocity low so ceiling registers and linear slot diffusers never whistle or draft.

01 · Manual J, S & D Calculation

Room-by-Room Heat Load & CFM Airflow Engineering

A west-facing upstairs bedroom with vaulted ceilings and glass doors in Westlake Village or Calabasas needs far more cooling CFM per square foot than a shaded downstairs guest room. We measure room geometry, window orientation, and static pressure before designing a single trunk or branch takeoff.

Typical tract-home shortcut: Guessing duct sizes by rule-of-thumb and daisy-chaining flex ducts off a stubby box plenum.

Rea's engineering standard: Dedicated supply and return sizing for every room, verified with digital manometers and airflow capture hoods.

02 · Custom Sheet-Metal Fabrication

Galvanized Plenums, Square-to-Round Transitions & Mastic Seals

Where air exits your indoor coil and enters the trunk is the highest-pressure zone in your entire HVAC system. We hand-fabricate heavy-gauge galvanized sheet-metal plenums with cross-broken panels, aerodynamic square-to-round transitions, canvas vibration-isolation collars, and brush-applied UL-181 mastic on every seam.

Typical tract-home shortcut: Leaky fiberglass duct board held together with peeling cloth tape that sheds fibers and leaks conditioned air into the attic.

Rea's engineering standard: Permanent sheet-metal plenums with labeled branch takeoffs and locking manual balancing dampers on every run.

03 · Return Air & Filtration Sizing

Eliminating High Static Pressure & Loud Return Grilles

If a system cannot inhale air quietly, it cannot push cool air to the far bedrooms. Many homes have a single undersized hallway return grille that whistles whenever the blower ramps up. We add dedicated bedroom jump-ducts or secondary return pathways and install deep-pleat hospital-grade media cabinets with near-zero pressure drop.

Typical tract-home shortcut: A restrictive 1-inch filter grille in the ceiling that roars like a vacuum cleaner and starves the blower motor.

Rea's engineering standard: Generous return air pathways and sealed 4–5 inch media filter cabinets that let your blower run at a whisper.

04 · Architectural Registers & Zoning

Linear Slot Diffuser Plenums & Independent Motorized Zoning

Whether you are keeping existing ceiling openings or upgrading to frameless architectural linear slot diffusers during a remodel in Malibu, Hidden Hills, or Beverly Hills, we fabricate insulated slot plenums and pair them with motorized variable-speed zoning across all major equipment brands—including Daikin, Mitsubishi, Lennox, Trane, and Carrier.

Typical tract-home shortcut: Dumping excess air into a bypass loop or closing dampers without variable-speed blower coordination.

Rea's engineering standard: Precision motorized dampers or dedicated concealed ducted air handlers paired with smart touchscreen zone controls.

Real Attic & Mechanical Room Proof

What Rea's Custom Ductwork & Plenum Craftsmanship Looks Like

Most homeowners never see inside their attic—which is why so many contractors cut corners up there. We build every attic and mechanical closet as if the ceiling were made of glass.

Concealed horizontal ducted unit with custom sheet-metal plenums and plywood service platform

Custom sheet-metal supply plenum transition

Labeled branch duct takeoffs with balancing dampers

Custom Sheet-Metal Plenums

Hand-Built Plenums, Labeled Takeoffs & Walkways

Every transition is fabricated to fit the exact attic geometry, sealed with UL-181 mastic, suspended on wide saddle straps every 4 feet with zero kinks, and surrounded by a full plywood walkway and bright LED work lighting.

Square-to-Round Transitions UL-181 Mastic Sealed Labeled Branch Dampers Plywood Walkways

Custom kitchen and living area with architectural linear slot diffusers

Open-concept living room with flush linear ceiling vents

Custom interior millwork with concealed air delivery

Architectural Air Delivery

Linear Slot Diffusers & Flush Register Integration

For custom homes and remodels in Westlake Village, Lake Sherwood, Malibu, and Beverly Hills, we build acoustic-lined plenums that feed slim linear slot diffusers—aligning cleanly with recessed lighting, ceiling beams, and custom cabinetry.

Linear Slot Plenums Acoustic Lining Draft-Free Mixing Room-by-Room Balance

Rea's HVAC crew on scissor lift beneath custom cross-broken sheet-metal plenum, square-to-round transition, and spiral trunk

In-house sheet-metal installers cutting overhead spiral galvanized duct on a Rea's HVAC scissor lift

Close-up of Rea's technician fabricating custom spiral galvanized ductwork

Rea's HVAC technician adjusting flush-mounted register on completed spiral duct run

Exposed Spiral & Custom Plenums

Square-to-Round Transitions & Heavy-Gauge Spiral Trunks

Custom-fabricated ceiling-suspended air handler plenum with cross-broken galvanized panels and a true square-to-round transition feeding rigid spiral ductwork—installed in-house by our crew.

Square-to-Round Transition Rigid Spiral Ductwork Cross-Broken Plenums In-House Fabrication

Completed Spiral Trunk · Unedited Walkthrough

Custom Sheet Metal & Spiral Ductwork in Action.

Watch our completed overhead spiral galvanized trunk, custom cross-broken supply plenum, aerodynamic square-to-round transition, and flush saddle registers—fabricated and hung on steel trapeze hangers by our in-house crew.

Square-to-round transition and cross-broken plenum

Square-to-Round Plenum

In-house spiral duct fabrication and cutting

In-House Fabrication

Ductwork & Airflow Questions

Common Questions About Ductwork Redesign & Hot/Cold Rooms

Straight answers on solving uneven upstairs temperatures, high static pressure, noisy vents, and aging attic ductwork.

Why are our upstairs bedrooms still hot even when the air conditioner runs non-stop?

In most two-story homes, the problem isn't the outdoor condenser—it's restrictive, undersized builder flex duct, a choked return plenum, and high external static pressure in a 135°F attic. By replacing pinched transitions with custom sheet-metal plenums, sizing branch trunks via ACCA Manual D, and adding independent upstairs/downstairs zoning, we deliver full, quiet cooling to upstairs bedrooms.

Can you redesign the ductwork on our existing HVAC system regardless of brand?

Yes. Whether your home runs Daikin, Mitsubishi, Lennox, Trane, Carrier, or another major platform, airflow physics are universal. We redesign plenums, return pathways, and supply trunks to match your equipment's exact blower curve and static pressure specification.

What makes custom sheet-metal plenums and square-to-round transitions better than standard duct board?

Fiberglass duct board and sharp 90-degree flex turns create severe air turbulence, whistling vents, and fiber erosion over time. We fabricate heavy-gauge galvanized sheet-metal plenums with aerodynamic square-to-round transitions, cross-broken panels, manual balancing dampers, and UL-181 mastic seals that last for decades.

Do you fabricate custom plenums for architectural linear slot diffusers?

Yes. Linear slot diffusers require acoustic-lined sheet-metal plenums engineered for low face velocity so air mixes gently across the ceiling without whistling or drafts. We coordinate directly with homeowners, remodelers, and architects to align slots cleanly with lighting and millwork.

Local Communities We Serve

Custom Ductwork & Airflow Redesign Across Our Service Area

We serve homeowners, architects, and custom builders across the Conejo Valley, Malibu, and the Westside from our Simi Valley headquarters.

Westlake Village

91361 & 91362 · North Ranch · Lake Sherwood · Westlake Island · Country Club Estates · Three Springs · First Neighborhood · Foxmoor Hills

Quiet, even comfort, custom attic ductwork, and clean indoor air for homes and custom builds in Westlake Village, North Ranch, and Lake Sherwood.

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Malibu

90265 · Serra Retreat · Carbon Beach · Point Dume · Malibu Colony · Broad Beach · Malibu Road · Encinal Bluffs · Latigo Canyon · Winding Way

Salt-air protected systems, sunlit glass-room temperature control, and automatic wildfire-smoke protection across coastal and canyon Malibu.

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Hidden Hills

91302 & 91307 · Hidden Hills Gated Community · Long Valley Road · Round Meadow · Ashley Ridge · Bell Canyon · The Oaks

Whisper-quiet outdoor placement, custom ductwork, and whole-property climate control for main residences, guest houses, and equestrian estates.

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Calabasas

91302 · The Oaks of Calabasas · Calabasas Park Estates · Bell Canyon · Mountain View Estates · Westridge · Hidden Hills Border · Monte Nido

Fixing uneven two-story temperatures, upgrading noisy equipment, and designing custom comfort for gated Calabasas communities.

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Thousand Oaks

91360, 91361, 91362 & 91320 · Sherwood Country Club · Lake Sherwood · North Ranch · Lynn Ranch · Sunset Hills · Dos Vientos Ranch · Lang Ranch · Winding Way

Manual J/D load design, clean attic craftsmanship, and quiet variable-speed heating and cooling across Thousand Oaks.

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Agoura Hills

91301 & 91377 · Old Agoura · Morrison Ranch · Chesebro Canyon · Medea Valley · Lake Lindero · Malibu Lake

Variable-speed comfort built for canyon temperature swings, plus automatic fresh-air shutoff during smoke season.

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Oak Park

91377 · Morrison Ranch Estates · Shadow Ridge · Country Glen · Saddle Peak · Montego · Regency Hills

High-efficiency heat pump upgrades, balanced upstairs/downstairs airflow fixes, and clean indoor air for Oak Park residences.

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Beverly Hills

90210, 90211, 90212 & 90077 · Trousdale Estates · The Flats · BHPO · Bel Air · Holmby Hills · Benedict Canyon

Invisible linear slot air delivery, quiet property-line acoustics, and responsive White Glove care for Westside estates.

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By Appointment

Schedule an Airflow & Ductwork Evaluation

Whether you want to solve hot upstairs bedrooms, silence noisy ceiling grilles, replace aging attic ductwork, or plan custom linear slot diffusers for a remodel, Riley Rea or a senior team member will get back to you personally.

Email: reashvac@gmail.com

Service Area: Westlake Village, Thousand Oaks, Agoura Hills, Oak Park, Calabasas, Hidden Hills, Malibu & Beverly Hills

License: California C-20 Warm-Air Heating, Ventilating & Air-Conditioning #1086780

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