Greenheck RVE · CaptiveAire DOAS · Reznor · Modine · Indirect-Fired and Direct-Fired
Make-Up Air System Repair Los Angeles
MUA unit service for replacing exhausted air across LA, OC, Ventura, Riverside. Heat exchanger, igniter, VFD, damper actuator. (424) 325-0520
Our Branches
8 service territories across Southern California
Make-Up Air System Repair
Southern California
MUA service
Why make-up air repair requires combustion-savvy diagnostics, not just appliance repair.
Make-up air (MUA) systems replace the air exhausted by Type I hoods. By code, exhaust fans on Type I hoods must run interlocked with MUA units; if the MUA isn't operational, the exhaust fan won't start. Without functional MUA, kitchen pressure goes negative when exhaust runs, which causes back-doors to slam, gas appliances to misfire (improper combustion air), and HVAC imbalance throughout the building. Climate-controlled MUA also heats incoming air in winter and cools in summer so the kitchen doesn't get blasted with outdoor temperature.
We service MUA systems across LA, Orange, Ventura, San Bernardino, Riverside counties. Greenheck is the dominant US market brand (Schofield WI), with the RVE indirect-fired model the most common in LA-area commercial kitchens. CaptiveAire DOAS series is common when paired with CaptiveAire exhaust hoods (single-vendor design). Reznor and Modine are common in older installations and value-tier new construction.
Common service items: heat exchanger (indirect-fired models, year 10 to 15 typical), igniter plus flame sensor (gas-fired, year 5 to 8), variable speed drive (modern units, year 8 to 12), damper actuators (multiple positions, sequence-critical), belt drive system, filter system (large MERV filters), roof-mounted unit weather damage (LA sun plus occasional rain). Combustion analysis on gas-fired units is required after any heat-side repair.
$120 commercial diagnostic, waived with repair. BHGS #A49573 plus EPA 608 Universal #1346255700410 plus CSLB C-20 HVAC. BBB A+. Phones answered 24/7. License verifiable.
Brand notes
What we see by brand on MUA service calls.
Greenheck. Schofield WI. Dominant US market share. RVE indirect-fired model is the most common in LA-area commercial kitchens (heat exchanger separates combustion gases from supply air, safer for food service). Direct-fired variants also common (gas burner directly heats supply air, more efficient but combustion analysis critical). Greenheck parts via Greenheck distribution (3 to 5 day standard ship). Accurex (Greenheck's hood brand) parts share some commonality with Greenheck MUA parts.
CaptiveAire DOAS. CaptiveAire's MUA line, common when the operator chose CaptiveAire for hoods plus MUA as single-vendor design. Variable speed drive standard on DOAS variants. Service via CaptiveAire dealer network.
Reznor. Older installations and value-tier new construction. Gas-fired primary. Service items concentrate at igniter, flame sensor, gas valve, heat exchanger.
Modine. Similar profile to Reznor: older installations, value-tier new construction. Common in commercial kitchens built before 2010.
Common scenarios
Top MUA repairs we see in our 5-county territory.
- Igniter plus flame sensor (gas-fired models). Year 5 to 8 typical. MUA won't start on heat call; combustion analyzer plus visual inspection identify fault. $300 to $560.
- Variable speed drive replacement (modern units). Year 8 to 12. VFD fault stops fan or causes erratic speed control. Greenheck and CaptiveAire DOAS use VFDs on standard configurations. $1,000 to $1,400.
- Damper actuator service. MUA systems have multiple dampers (intake, mixing, exhaust). Damper sequence is critical for proper airflow. $440 to $720 per actuator.
- Belt plus pulley replacement. Belt-driven variants, year 4 to 7. $260 to $440.
- Make-up air interlock diagnostic. When exhaust fan won't start, the issue is often MUA-side. Diagnose interlock chain to identify which MUA component is breaking the circuit. $340 to $620.
- Filter system service. Large MERV filters require periodic replacement. Filter resistance affects MUA fan efficiency and amp draw. $140 to $320 per filter set.
- Heat exchanger replacement (indirect-fired models). Year 10 to 15 typical. Heat exchanger leaks are safety-critical (combustion byproducts entering supply air). Diagnosed with combustion analyzer plus pressure test. $1,800 to $3,200 typical replacement.
- Roof-mounted unit weather damage. LA sun plus occasional rain. Cabinet seals, control box gaskets, weatherproofing. Variable cost depending on damage extent.
- Combustion analysis post-repair. Required on gas-fired units after any heat-side service. We carry combustion analyzer on every MUA call.
- Roof access logistics. MUA units are typically rooftop. Access via ladder (single-story), freight elevator (high-rise with building maintenance access), or lift rental (multi-story restricted access).
Real repairs
Composite stories from the route.
Four MUA repair jobs from the past 90 days. Brand, model context, symptoms, diagnosis, parts, time, total. Names omitted; the technical scenarios are typical of what we see weekly.
High-volume restaurant in West Hollywood · Greenheck RVE indirect-fired heat exchanger leak
MUA on heat call, combustion analyzer flagged elevated CO at supply diffuser. Diagnostic: heat exchanger pinhole leak. Replacement on indirect-fired RVE heat exchanger required full MUA cabinet disassembly plus crane access for replacement section. Total: $1,800. Combustion analysis post-repair confirmed safe levels. 13-year unit; cabinet excellent condition for continued service.
Hotel kitchen in Pasadena · CaptiveAire DOAS variable speed drive
MUA fan running erratic, sometimes overspeeding on startup. Diagnostic: VFD fault, intermittent speed control. Replaced VFD with CaptiveAire OEM. Tested through full speed range and interlock with paired exhaust fans. Total: $1,200. 9-year unit; service life matches expected 8-12 year VFD window.
Restaurant chain in Long Beach · Reznor MUA igniter plus flame sensor
MUA wouldn't start on heat call. Diagnostic: igniter cracked, flame sensor coated with oxide. Replaced both as paired service. Combustion analysis post-repair confirmed proper combustion. Total: $560. Quick fix; common 5-8 year service item on gas-fired Reznor.
Commercial kitchen in Beverly Hills · Greenheck damper actuators (multiple)
Multi-damper system: intake, mixing, exhaust. Two of three actuators failed simultaneously (paired wear pattern). Replaced both failed actuators plus inspected third. Tested damper sequence through full operational range. Total: $890 (two actuators plus diagnostic plus inspection). 11-year system; sequence-critical components were original equipment.
Scope
What we do for MUA repair, and what we don't.
We service: Greenheck RVE indirect-fired plus direct-fired MUA, CaptiveAire DOAS series, Reznor, Modine. Heat exchanger replacement, igniter plus flame sensor service, variable speed drive replacement, damper actuator service, belt drive replacement, filter system service, combustion analysis on gas-fired units, make-up air interlock diagnostic for exhaust fan integration. Roof access coordination across single-story, multi-story, and high-rise buildings.
We don't do: new MUA installation (commercial HVAC contractor trade with crane and structural roof modification scope); ductwork sizing redesign (sheet-metal contractor plus mechanical engineer trade); structural roof penetration sealing (roofing contractor trade). We coordinate with all of these when you need a combined project.
For Type I hood and cleaning service: see our Type I hood repair and hood cleaning service sister pages. MUA is part of the same exhaust-hood system; combined dispatch is standard.
Pricing
Make-up air system repair costs.
Diagnostic is $120 (commercial tier), waived with repair. Roof access lift rental adds $300 to $800 on multi-story or restricted-access buildings. Combustion analysis post-repair is included on gas-fired heat-side service.
| Repair | Typical Cost |
|---|---|
| Diagnostic | $120, waived with repair |
| Igniter plus flame sensor (gas-fired) | $300 to $560 |
| Variable speed drive replacement | $1,000 to $1,400 |
| Damper actuator (per actuator) | $440 to $720 |
| Belt plus pulley replacement | $260 to $440 |
| Make-up air interlock diagnostic | $340 to $620 |
| Filter set replacement (per set) | $140 to $320 |
| Heat exchanger replacement (indirect-fired) | $1,800 to $3,200 |
| Roof weatherproofing repair | $280 to $620 |
| Combustion analysis (included with heat-side service) | Included |
| Multi-component repair (aged systems) | $1,400 to $3,400 |
| Roof access lift rental (multi-story) | $300 to $800 added to service ticket |
| Warranty (SDAR labor) | 90 days parts and labor |
Why operators choose us
What separates our MUA service from general HVAC repair.
- Combustion analyzer on every MUA call. Required for safe service of gas-fired units. Post-repair analysis included on heat-side work.
- Make-up air interlock diagnostic expertise. When exhaust fan won't start, diagnose the interlock chain to identify the MUA-side component instead of replacing the exhaust fan motor unnecessarily.
- Brand-specific knowledge. Greenheck RVE, CaptiveAire DOAS, Reznor, Modine have different parts networks and service procedures.
- Indirect-fired heat exchanger safety awareness. Heat exchanger leaks on indirect-fired MUA are safety-critical (CO and NOx in supply air). Treated as priority dispatch.
- Roof access logistics. Lift rental coordination, building maintenance freight elevator scheduling, multi-story access planning.
- Combined exhaust hood plus MUA dispatch. When both need service, single visit covers everything; saves on repeat dispatch.
- BHGS #A49573 plus CSLB C-20 HVAC plus EPA 608 Universal #1346255700410. Verifiable.
- 24/7 phone answering.
- Same-day across LA, OC, Ventura. Next-day RC, Temecula.
FAQ
Make-up air system repair questions.
What does the make-up air system actually do?
The MUA replaces the air exhausted by your Type I hood. By code, exhaust fans on Type I hoods must run interlocked with make-up air units; if the MUA isn't operational, the exhaust fan won't start. Without the MUA, your kitchen pressure goes negative when the exhaust fan runs, which causes back-doors to slam, gas appliances to misfire (improper combustion air), and HVAC system imbalance throughout the building. Climate-controlled MUA also heats incoming air in winter and cools in summer so the kitchen doesn't get blasted with outdoor temperature.
Do you service Greenheck, CaptiveAire DOAS, Reznor, and Modine?
Yes. Greenheck is the dominant US market brand (Schofield WI), with the RVE indirect-fired model the most common in LA-area commercial kitchens. CaptiveAire DOAS series is common when paired with CaptiveAire exhaust hoods (single-vendor design). Reznor and Modine are common in older installations and value-tier new construction. We have brand-specific knowledge across the four.
My MUA heat exchanger is leaking. How serious?
Heat exchanger leaks on indirect-fired MUA units (gas-fired with sealed heat exchanger separating combustion gases from supply air) are serious. A leak means combustion byproducts (carbon monoxide, NOx) can enter the kitchen air supply. We diagnose with combustion analyzer plus heat exchanger pressure test. Repair on indirect-fired heat exchangers is typically not feasible; replacement runs $1,800 to $3,200 depending on unit size. On direct-fired MUA units (no heat exchanger; gas burner directly heats the air stream) this isn't a concern but combustion analysis is still required after service.
Why does my exhaust fan keep tripping the make-up air interlock?
Exhaust fan and MUA are interlocked by code: exhaust can't run without MUA. Interlock faults usually trace to MUA-side failures (not exhaust fan failures). Common causes: MUA igniter failure on gas-fired models (won't start, so interlock won't permit exhaust), MUA variable speed drive fault on modern units, damper actuator failure preventing MUA airflow, sensor wiring damage. We diagnose the interlock chain and identify which component is breaking the cycle.
How long do MUA systems last?
Heat exchangers (gas-fired indirect models) typically 10 to 15 years. Igniter and flame sensor 5 to 8 years on gas-fired. Variable speed drives 8 to 12 years on modern units. Belt drive systems 4 to 7 years on belt-driven variants. Roof-mounted units in LA are exposed to sun and occasional rain; weather damage is possible but typically gradual. Cabinet itself outlasts components by decades on premium brands.
What does MUA repair cost in LA?
$120 commercial diagnostic, waived with repair. Common repairs: igniter plus flame sensor $300 to $560, variable speed drive replacement $1,000 to $1,400, damper actuator $440 to $720, belt plus pulley $260 to $440, heat exchanger replacement $1,800 to $3,200 (indirect-fired models), filter replacement $140 to $320 per filter set. Multi-component repair on aged systems $1,400 to $3,400. Roof access lift rental adds $300 to $800 on multi-story or restricted-access buildings.
What's your warranty?
90 days SDAR labor warranty on every repair. Greenheck, CaptiveAire, Reznor, Modine component warranties processed separately through manufacturer authorized networks. BHGS #A49573 plus EPA 608 Universal #1346255700410 plus CSLB C-20 HVAC.
Related
Exhaust hood service across the catalog.
MUA System Down? Call Today.
Greenheck, CaptiveAire DOAS, Reznor, Modine specialists. Combustion-savvy diagnostics. Same-day across LA, OC, Ventura. BHGS #A49573 and EPA 608 Universal #1346255700410.