Makeup Air Units
Makeup air units replace exhausted air in commercial and industrial buildings to maintain proper pressurization and air quality.
Knape Associates provides direct-fired, indirect-fired, and DOAS systems from manufacturers including AbsolutAire, Captiveaire, and other major manufactures for facilities across Texas and the US.
MAUs prevent negative pressure that reduces exhaust performance by up to 30% and creates backdrafting hazards. Required by code when kitchen exhaust exceeds 400 CFM (IMC Section 505), for spray booth operations (OSHA 29 CFR 1910.94), and in warehouses meeting ASHRAE 62.1 ventilation standards.
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Our Makeup Air Unit Solutions
Direct-Fired Makeup Air Units
Burns natural gas or propane directly in the airstream for 92% thermal efficiency. Heats incoming air from ambient to 50-70°F in single pass.
Suitable for warehouses, manufacturing plants, and industrial facilities where combustion byproducts in supply air meet application requirements.
Standard capacities: 2,000-100,000 CFM. Lead time: 10-14 weeks. Custom burner configurations add 2-3 weeks.
Indirect-Fired Makeup Air Units
Uses heat exchanger to separate combustion products from supply air. Thermal efficiency drops to 78-82% but delivers contaminant-free air required for food processing, pharmaceutical manufacturing, and clean room applications.
Standard capacities: 1,500-75,000 CFM. Lead time: 12-16 weeks. Stainless steel heat exchangers add 3-4 weeks.
Dedicated Outdoor Air Systems (DOAS)
Conditions outdoor air for ventilation with integrated cooling, heating, and dehumidification. Maintains precise temperature and humidity control for occupied spaces.
Common in office buildings, schools, and healthcare facilities requiring year-round climate control.
Standard capacities: 500-50,000 CFM. Lead time: 14-18 weeks. Energy recovery wheels add 2-3 weeks.
Custom Industrial MAUs
Engineered for spray booths, welding operations, and specialized manufacturing processes. Available with explosion-proof ratings (Class I Division 1 and 2), corrosion-resistant materials, and non-standard configurations.
Lead time: Varies depending on certifications and materials. Explosion-proof certification are available.
MUA Applications We Serve
Make up air units for Commercial Kitchens
IMC Section 505 requires makeup air when exhaust exceeds 400 CFM. NFPA 96 Section 8.3.1 limits negative pressure to 0.02 inches water column (4.9 Pa). Supply air matches 75-80% of exhaust rate to maintain slight negative pressure while preventing backdrafting.
Typical restaurant applications: 3,000-8,000 CFM per hood. Multi-hood installations require 10,000-30,000 CFM total capacity.
Warehouses & Distribution Centers
ASHRAE 62.1 establishes minimum 0.06 CFM per square foot for warehouse ventilation. 100,000 sq ft facility requires 6,000 CFM baseline, increasing with forklift operations or chemical storage. Air change rates typically 6-30 ACH depending on contamination levels and door traffic.
Temperature differential limited to 10°F above or below space temperature per IMC Section 508.1.1.
Spray Booth Operations
OSHA 29 CFR 1910.94 mandates makeup air for all spray finishing operations. NFPA 33 Section 7.2.3 requires makeup air when building volume is less than 20× exhaust fan capacity.
System must operate during spraying and sufficient time afterward to clear flammable vapors.
Explosion-proof ratings required. Class I Division 1 for interior spray areas, Division 2 for adjacent spaces.
Manufacturing & Industrial Facilities
Process exhaust from welding, grinding, chemical handling, or heat-generating equipment creates negative pressure requiring dedicated makeup air.
Custom materials handle corrosive environments. Stainless steel or specialty coatings available for chemical exposure.
Direct-Fired vs Indirect-Fired Comparison
| Feature | Direct-Fired | Indirect-Fired |
|---|---|---|
| Thermal Efficiency | 92% | 78-82% |
| Combustion Products | Enter supply air | Separated via heat exchanger |
| Operating Cost | Lower (higher efficiency) | Higher (efficiency loss) |
| Applications | Warehouses, manufacturing, industrial | Food processing, pharmaceuticals, clean rooms |
| Lead Time | 10-14 weeks | 12-16 weeks |
| Initial Cost | $8,000-$45,000 (depending on CFM) | $12,000-$65,000 (depending on CFM) |
| Code Restrictions | Prohibited in some clean air applications | Meets all air quality standards |
| Maintenance | Burner inspection annually | Heat exchanger cleaning + burner inspection |
When to Specify Direct-Fired
Combustion byproducts (water vapor and COâ‚‚) acceptable in supply air. Meets code for warehouses, general manufacturing, and non-food industrial facilities. Lower operating costs justify specification when air quality restrictions don’t apply.When to Specify Indirect-Fired
Required for food processing (FDA regulations), pharmaceutical manufacturing (cGMP compliance), and facilities where combustion products contaminate processes or products. Specify when local codes prohibit direct combustion in supply air or when serving occupied spaces requiring IAQ certification.Why Choose Knape Associates
Multi-Manufacturer Sourcing
Access to 20+ makeup air manufacturers including CaptiveAire, Halton, Sterling HVAC, and AbsolutAire. Compare specifications, lead times, and pricing across brands to match project requirements and budget constraints.
Engineering Support
Licensed mechanical engineers review CFM calculations, verify code compliance, and validate system sizing. Prevent common specification errors including undersized units, incorrect pressurization targets, and inadequate filtration.
Nationwide Coverage
Serve commercial and industrial projects across the United States. Ship makeup air units, replacement parts, and accessories to contractors, facility managers, and project engineers nationwide.
Installation Coordination
Coordinate with mechanical contractors for rigging, electrical requirements, and gas line sizing. Provide submittal packages, shop drawings, and commissioning support for projects requiring engineer approval.
40+ Years Industrial Equipment Experience
Since 1982, Knape Associates has specified heating, cooling, and ventilation equipment for refineries, chemical plants, manufacturing facilities, and commercial buildings. Direct relationships with factory representatives ensure accurate lead times and technical support.