> By: The Cooling Company
plenum box replacement cost: get accurate estimates and save (ASHRAE Technical Resources) A plenum box replacement can range from a few hundred dollars to tens of thousands. Small supply plenums often cost $800–$6,000. Large, code-triggered or hard-access projects can exceed $30,000. Budget for dampers, TAB testing, permits, and hidden remediation when you request contractor bids.
Key Takeaways
- Use a room-by-room Manual J load calculation (not a square-foot rule).
- Select equipment with Manual S and verify ducts with Manual D for comfort and efficiency.
- Avoid oversizing: short-cycling wastes fuel and can create uneven temperatures.
Plenum Box Replacement Cost - Key takeaways
This section summarizes the cost ranges and the most common factors that change bids. Small supply plenums commonly sit in the $800–$6,000 band. Mid-size projects often land in the $6,000–$30,000 range. Large or complicated projects can exceed $30,000 when you add specialized dampers, strict testing requirements, or remediation work.
Major cost drivers include access, dampers, insulation, TAB testing, permits, and hidden remediation. A clear contract should require shop drawings, UL-listed dampers where required, and a TAB report. Ask bidders to show allowances and unit prices. That helps you compare proposals side-by-side and reduces surprise change orders.
Typical cost bands and what they mean
Small jobs are usually simple supply boxes in easy-access locations. These require less labor and standard materials. Mid-size jobs often include multiple dampers or controls and may need partial shutdowns. Large jobs add coordination, infection control, firestopping, and complex sequencing. Understanding the band helps you set a realistic budget and contingency.
How to use the key takeaways when budgeting
Use the ranges to build an initial budget and then add a 10–25% contingency for hidden issues. Require bidders to break down costs into demolition, fabrication, dampers, insulation, TAB, permits, and allowances. When allowed items are listed, you can see which bid gives more true value versus which simply has a low headline price.
What is a plenum box and why replace it?
A plenum box is a metal chamber that directs conditioned air from the air handler into branch ducts. It forms a node where the main supply connects to several takeoffs. When the box leaks, it can let conditioned air bypass ductwork, hurt pressure balance, and reduce filter effectiveness. That can cut comfort and increase energy costs.
Replace a plenum box when seams separate, insulation collapses, or fire and smoke barriers are compromised. Wet or rusted material, widespread tape repairs, and failing joints are usual signs. Proper replacement restores designed leakage class and brings airflow back to expected values. It can also preserve fire-rated boundaries and reduce long-term repair cycles.
How does a plenum box affect HVAC performance?
Airflow needs smooth, sealed plenums and proper transitions at each takeoff. A damaged plenum creates uneven CFM at diffusers. That forces fans to run longer and raises energy use. Fixing or replacing the box can reduce run hours and improve comfort, especially in problem zones with weak airflow.
A sealed plenum also supports correct system pressure. Pressure balance affects return and supply paths, economizer function, and ventilation rates. If the plenum leaks into unconditioned spaces, fans must overcome added losses and the HVAC system no longer performs to design.
What causes plenum box failure?
Common causes include corrosion, vibration, and poor past repairs. Condensation that lacks a proper vapor barrier will soak insulation and speed decay. Repeated thermal cycling and mechanical damage at seams also lead to failures over time. Older boxes often show multiple small repairs instead of a robust fix.
Hidden damage above ceilings and inside interstitial spaces can grow until leakage causes performance or code failures. Routine inspection and diagnostic testing catch many issues early. If you see signs of moisture, rust, or mold, plan for further inspection before finalizing repair options.
When is repair enough versus full replacement?
Minor seam leaks and localized insulation damage can be repaired and wrapped. That extends service life and can be cost effective. However, replace the box when most seams fail, fire barriers are compromised, or mold and asbestos are present. Once performance tests show high leakage, replacement is usually the better long-term value.
Make decisions using diagnostic data. Have a bidder or independent tester measure leakage and pressure before you approve a repair-only scope. That prevents repeat work and helps predict energy savings after the fix.
What drives plenum replacement costs?
Several factors drive cost. Materials, difficulty of access, required dampers, and testing needs form the bulk of the price. Shop fabrication time and field labor are major line items. Hidden items such as asbestos, mold, or required firestopping often add permit and remediation fees.
Plan budgets with a 10–25% allowance for unforeseen conditions. Job size matters a lot. Small retail or single-supply plenums often stay under $6,000. Mid-size office or rooftop assemblies commonly range $6,000–$30,000. Large healthcare or multi-floor projects climb above $30,000 due to coordination and strict testing needs.
How do material choices change cost?
Material choice has a direct effect on price. Galvanized G90 steel is the lowest-cost option and works well in dry spaces. Stainless or coated metals raise material cost and can add 20–100 percent to the material line. These choices matter where moisture or corrosion risk is high.
Insulation and vapor barriers also affect price. Higher R-value or foil-faced insulation adds both material and labor costs in humid or cold climates. Specify the insulation type you expect in the scope so bidders use comparable materials.
How does labor and shop time factor in?
Shop labor covers drawings, prefabrication, and assembly work. Field labor includes demolition, tie-ins, sealing, and insulation. Local hourly rates vary, but many markets see $75–$150 per hour per technician. Complex projects require more man-hours and coordination, which raises final bids.
Also consider travel, mobilization, and special access equipment. Restricted interstitials and high ceilings increase labor and safety costs. Scaffolding, lifts, or confined-space work add both time and permit needs.
What permit and inspection fees apply?
Permit fees depend on jurisdiction and project value. Expect plan review and scheduled inspections when you alter fire-rated assemblies or install UL-listed dampers. Some cities require licensed sheet-metal contractors and stamped shop drawings. Permit timelines can extend project duration and should be in schedules.
Factor permit fees and inspection windows into the bid evaluation. Missing required permits can cause rework and delay final payments. Contractors should state permit responsibility in their proposals.
Dampers, controls, and testing costs
Dampers and controls can be a large portion of the cost when code requires UL-listed devices. Manual dampers are low cost but often not code compliant where fire or smoke containment is required. UL-listed fire and smoke dampers with actuators and linkages are more expensive but necessary for life safety.
Testing and balancing (TAB) costs vary with system size. TAB validates CFM and leakage and gives you a post-work performance baseline. Independent testing is especially important on projects that must meet code or owner acceptance criteria.
What are typical damper and actuator prices and UL ratings?
Basic manual dampers may be a few hundred dollars each installed. UL-listed fire or smoke dampers with actuators often cost $1,000–$6,000 each installed and tested. Actuator and control integration adds costs based on wiring and BMS needs. Count dampers early to avoid scope surprises.
Ask for product data sheets and UL listing numbers in bids. Require that installers provide the labels and documentation in the closeout package. That makes inspection easier and prevents costly corrections later.
What is the role of TAB and balancing reports?
TAB confirms design CFM distribution, measures leakage, and verifies pressures after work is complete. Reports should show test methods, measured CFM, and any corrective actions taken. They often follow AABC or NEBB standards.
When code or owners require documented verification, hire an independent TAB firm. Independence reduces conflicts of interest and provides defensible test results. Small systems may only need a simple report, but large systems often require full commissioning.
What installer qualifications matter?
Require licensed sheet-metal contractors and HVAC techs experienced with fire-rated assemblies. Manufacturer-authorized installers and crews familiar with UL damper installation add value. Ask for references on similar projects and sample shop drawings.
Verify that the contractor has done balancing work and provided TAB reports before. A firm with coordinated shop and field workflow reduces change orders and speeds closeout.
How to get accurate contractor quotes
Accurate bids depend on clear scopes and consistent information to each bidder. Provide the same documents, photos, and acceptance criteria to everyone who bids. Require shop drawings and a TAB deliverable to avoid ambiguity. Ask for references and check licensing and insurance.
Have bidders break out allowances and unit prices for change items. That makes side-by-side comparison possible and reduces surprise change orders. Require bidders to state workmanship standards like SMACNA and to define leakage targets rather than only thickness or gauge.
What info should bids include?
Bids should list materials, labor hours, access requirements, and damper counts. They should include TAB allowances, permit fees, and any remediation assumptions. Ask for workmanship standards, leakage targets, and reference to applicable specifications.
A clear bid minimizes disputes and speeds approvals. If special phasing or infection-control measures are needed, require bidders to include those costs and plans explicitly.
How to write a clear scope of work?
Define demolition limits, sealing standards, insulation type, and leakage class in the scope. State whether the contractor must provide shop drawings, pull permits, and deliver TAB reports. Describe coordination windows for occupied areas and any shutdown constraints.
Including acceptance criteria and testing obligations prevents rework. Specify how allowances will be handled and require notification procedures for discovered conditions. That keeps projects on schedule.
Can you compare unit prices and allowances?
Yes. Ask bidders to break out per-linear-foot and per-square-foot rates, plus a per-damper price. Include allowances for asbestos testing, ceiling repair, and unforeseen penetrations. This approach makes change orders predictable.
Compare unit rates rather than only lump sums. Unit pricing shows where a contractor might be low on one item but high on another. It also helps you vet reasonableness when permit or remediation needs arise.
Safety, codes, and fire concerns
Plenum replacement touches life-safety systems and building codes. Missing UL-listed dampers or improper penetrations can force expensive rework and compromise occupant safety. Engage code officials early when the plenum crosses fire-rated assemblies or smoke barriers.
Document every penetration and installed damper with photos and labeled shop drawings. That streamlines permit closeouts and reduces the risk of failed inspections. In hospitals or labs, add infection-control and sequencing requirements to protect occupants.
How does plenum replacement affect fire safety?
Opening a plenum can create new paths for smoke and fire without proper sealing. Installing UL-listed dampers and preserving fire-rated barriers prevents unsafe smoke spread. Final labeling and inspection by the authority having jurisdiction ensure life-safety systems remain effective.
Contractors should follow tested installation methods and provide documentation for all fire and smoke assemblies. This reduces the chance of expensive corrections after inspectors review the work.
What NFPA and local codes apply?
NFPA 90A covers ventilation and air-conditioning systems and sets fire-resistance expectations. UL 555 and UL 555S cover fire and smoke damper testing and installation. Local codes may adopt these or set stricter rules.
Always check with the local authority having jurisdiction for interpretation and additional requirements. Early contact prevents costly scope changes late in the job.
How to ensure smoke containment is intact?
Have a qualified inspector check all penetrations and damper installations after work is complete. When required, perform smoke testing and provide written verification of compliance. Keep fire-stopping details and UL assembly labels in the closeout package.
Retain final test reports and photos for future audits or tenant turnovers. Those records speed inspections and help owners validate long-term code compliance.
How is a plenum replacement scoped, priced, and closed out?
A clear bid separates demolition, fabrication, dampers, insulation, TAB, permits, and allowances as line items. Include mobilization and travel fees for remote projects. Ask bidders to show taxes, overhead, and profit separately for transparency.
Estimate a 10–25 percent contingency for hidden issues in older buildings. When asbestos testing is likely, require testing before demolition. Large jobs may need phased plans to keep the building running while replacements occur.
What line item costs should appear?
Key line items include demolition, new plenum fabrication, insulation, dampers, actuators, controls integration, TAB, and permits. Show unit prices for extra dampers and per-foot sheet metal charges. Include scaffolding and ceiling repair as separate items.
Clear line items make it easier to compare bids and to approve change orders. They also help owners track spend as the project progresses.
How to model energy savings and payback
Sealing a leaky plenum reduces fan power and run hours. Use pre- and post-TAB data, fan curves, and run hours to estimate saved kWh. Multiply saved kW by run hours and local energy prices for simple payback. An energy engineer or experienced contractor can build a basic model from TAB inputs.
Small fixes may have long paybacks, sometimes over ten years. Larger sealed systems with major leakage often see paybacks under five years. Use actual measured data to avoid guesswork and to justify investment.
Procurement checklist and closeout items
A useful checklist includes scope, shop drawings, damper count, TAB inclusion, permit responsibility, allowances, schedules, mobilization fees, and warranty terms. Require final test reports, labeled dampers, and inspection sign-offs before final payment.
Keep all documents for future building audits. Stamped drawings, UL listings, TAB reports, and photos form the permanent record that protects owners and simplifies future work.
Ready to get quotes and compare contractors?
Use the procurement checklist above when you ask for shop drawings, damper counts, TAB scopes, and unit prices. Get at least three detailed quotes and compare them side-by-side. This approach reduces surprises and helps you select the best value, not only the lowest price.
Las Vegas area homeowners can call The Cooling Company at 17029308411 for a free site assessment and detailed quote. Our licensed techs serve Las Vegas, Henderson, and North Las Vegas. We provide shop drawings, UL-listed damper installs, and TAB reporting when codes demand them.
How to request sample quotes from contractors
Provide plans, photos, a clear scope, and damper counts when you request bids. Ask bidders to list mobilization, permits, and TAB as separate line items. That keeps bids comparable and highlights true cost differences between installers and fabricators.
If you are outside our service area, ask for NATE-certified technicians, UL-listed damper installs, and an independent TAB report. Those items protect your investment and life safety.
Call to action: Request a free site assessment
Las Vegas, Henderson, or North Las Vegas customers: call The Cooling Company at 17029308411 for a free site assessment and a detailed, itemized quote. If you are outside our service area, ask for NATE-certified technicians, UL-listed damper installs, and an independent TAB report. Those items protect your investment and life safety.
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About The Cooling Company
The Cooling Company has been serving the Las Vegas valley with professional HVAC services for over a decade. Our team of licensed, NATE-certified technicians specializes in air conditioning repair, heating system maintenance, and complete HVAC installations. We're committed to providing honest, reliable service with upfront pricing and a 100% satisfaction guarantee on all work performed.
- Phone: (702) 930-8411
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Service Areas
We proudly serve homeowners and businesses throughout the Las Vegas metropolitan area, including Las Vegas, Henderson, and North Las Vegas. Our service technicians are available for same-day appointments in most areas, with emergency service available 24/7 for urgent HVAC issues.
Sources
Primary technical guidance and sizing references can be found in the ASHRAE Technical Resources collection. For code and damper testing references, consult NFPA standards and UL listings cited in product data sheets and shop drawings.
- U.S. Department of Energy (Energy.gov) (accessed 2026-01-03)
- U.S. Environmental Protection Agency (EPA) (accessed 2026-01-03)
- ASHRAE (Standards and guidance) (accessed 2026-01-03)
- ENERGY STAR (Heating & cooling) (accessed 2026-01-03)
(ASHRAE Technical Resources: https://www.ashrae.org/technical-resources)