Selecting the right direct-fired make-up air burner is an important decision for original equipment manufacturers (OEMs) developing commercial and industrial heating equipment. The burner must deliver the required heating capacity while maintaining stable combustion, consistent temperature control, acceptable emissions, and compatibility with the complete air-handling system.
For manufacturers designing make-up air units, industrial ventilation equipment, automotive spray booths, and process heating systems, burner selection involves more than choosing a model based on BTU capacity. Engineers must consider airflow requirements, pressure differential, turndown capability, burner configuration, fuel type, and applicable safety standards.
Midco International works with OEMs to develop direct-fired burner solutions that support efficient equipment design, reliable combustion, and application-specific heating requirements. Our HMA burner line offers modular configurations and advanced combustion technology for a variety of commercial and industrial make-up air applications.
What Is a Direct-Fired Make-Up Air Burner?
A direct-fired make-up air burner heats air as it moves through a ventilation or air-handling system. Unlike indirect-fired heating equipment, which transfers heat through a heat exchanger, direct-fired systems introduce combustion heat directly into the supply airflow.
These systems are commonly used to replace air exhausted from commercial buildings, manufacturing facilities, industrial operations, and specialized ventilation equipment.
Direct-fired make-up air burners are frequently found in warehouses, commercial kitchens, manufacturing plants, automotive paint booths, and industrial drying applications.
Because combustion products enter the heated air stream, burner selection must account for airflow, combustion quality, emissions, and the intended use of the equipment.
How Do OEMs Determine the Required Burner Heating Capacity?
One of the first steps in burner selection is calculating the heating capacity required for the application.
OEM engineers typically evaluate the volume of air being heated, the entering air temperature, and the desired discharge temperature.
For standard air conditions, a common heating calculation is:
BTU/hr = 1.08 × CFM × Temperature Rise (°F)
For example, a make-up air unit moving 10,000 cubic feet per minute (CFM) with a required temperature rise of 60°F would need approximately 648,000 BTU/hr of useful heating capacity under standard air conditions.
Actual burner input requirements depend on factors such as air density, elevation, system losses, and operating conditions.
Selecting a burner that is improperly sized can create performance challenges. An undersized burner may struggle to maintain discharge temperatures, while an oversized burner may introduce control difficulties or unnecessary cycling.
Midco works with OEMs to evaluate heating capacity requirements and identify appropriate HMA burner configurations.
Why Are Airflow and Pressure Differential Important?
Direct-fired make-up air burners depend on proper airflow to maintain stable combustion and distribute heat throughout the air stream.
OEMs must evaluate the air velocity across the burner, the pressure differential available through the burner profile, and the overall airflow distribution within the equipment.
Insufficient airflow or uneven air distribution can affect flame stability, combustion quality, and temperature uniformity.
Midco’s HMA-2A burner platform is designed for a range of airflow conditions, making it suitable for different make-up air equipment configurations.
However, the burner must be integrated into a properly engineered air-handling system. Profile dimensions, blower placement, duct configuration, and pressure conditions all influence burner performance.
For OEMs developing new equipment, evaluating airflow early in the design process can reduce the likelihood of combustion problems during testing.
How Does Burner Turndown Affect Make-Up Air Performance?
Turndown refers to the ratio between a burner’s maximum and minimum stable firing rates.
A burner with a wide turndown range can adjust its heating output to match changing operating conditions.
This is particularly valuable for make-up air equipment operating in climates with significant seasonal temperature changes or facilities with variable ventilation requirements.
For example, an industrial ventilation system may require substantial heating during winter but considerably less heating during milder weather.
Midco’s HMA-2 and HMA-2A burners can support turndown ratios of approximately 30:1 when equipped with suitable modulation controls and gas train components.
High turndown capability can help OEMs achieve more precise discharge temperature control, reduce unnecessary burner cycling, and improve performance across varying heating demands.
The achievable turndown range must be confirmed for the specific burner configuration and operating conditions.
Why Does Burner Configuration Matter for OEM Equipment Design?
Every make-up air unit has different physical dimensions, airflow requirements, and installation constraints.
A burner that fits one equipment cabinet may not be appropriate for another.
Midco’s HMA burner line uses modular construction that allows OEMs to assemble burner configurations using different sections and components.
This flexibility supports the development of burner assemblies for various equipment sizes and heating capacities.
For manufacturers producing multiple make-up air unit models, modular burner design can simplify engineering, reduce component variation, and support more consistent manufacturing processes.
Important configuration considerations include burner length, available cabinet space, airflow profile dimensions, service accessibility, and required heating capacity.
Selecting the burner configuration during the early stages of equipment design can help avoid expensive modifications later.
What Role Do Combustion Efficiency and Emissions Play?
Combustion performance is a major consideration in direct-fired make-up air systems because combustion products enter the heated air stream.
Carbon monoxide (CO) and nitrogen dioxide (NO₂) emissions are particularly important for equipment safety and applicable certification requirements.
Poor combustion can result from improper air-to-fuel ratios, unstable flames, incorrect burner positioning, or inadequate airflow.
Midco’s HMA-2 and HMA-2A burners incorporate two-stage combustion technology designed to improve flame stability and support low-emissions performance.
The combustion process helps create a shorter, more stable flame while improving control over combustion characteristics.
For OEMs, selecting a burner with suitable emissions performance can simplify equipment development and help address the requirements of applicable safety standards.
However, emissions must be evaluated under the actual operating conditions of the complete heating appliance.
Which ANSI Standards Should OEMs Consider?
Different direct-fired heating applications may fall under different ANSI standards.
OEMs should determine the applicable standard based on the equipment’s intended use, airflow configuration, operating temperatures, and other design characteristics.
Three important standards include:
ANSI Z83.4: Covers non-recirculating direct gas-fired heating and forced ventilation equipment commonly used in commercial and industrial make-up air applications.
ANSI Z83.18: Addresses recirculating direct gas-fired heating and forced ventilation equipment that combines outdoor air with recirculated building air.
ANSI Z83.25: Covers direct gas-fired process air heaters used in qualifying industrial process heating applications.
The correct standard influences equipment design, safety controls, emissions testing, and certification procedures.
OEMs should verify the applicable edition and requirements with their certification organization before finalizing equipment specifications.
How Does Fuel Type Influence Burner Selection?
Fuel availability and gas characteristics are important factors when selecting a direct-fired make-up air burner.
Natural gas is commonly used in commercial and industrial heating systems, while propane may be preferred in facilities without access to natural gas infrastructure.
OEMs must account for fuel type, gas supply pressure, heating value, gas train configuration, and compatible burner components.
Midco’s HMA burner solutions support natural gas and appropriate propane applications, with certain configurations available for specialized fuel requirements.
Burner and gas train components must be selected and adjusted for the intended fuel.
Fuel conversions should only be performed using manufacturer-approved procedures and components.
What Should OEMs Consider About Burner Controls and Safety?
A direct-fired make-up air burner must operate as part of a complete heating and ventilation control system.
Proper burner controls help regulate heating output, monitor operating conditions, and shut down the system when unsafe conditions are detected.
Depending on the equipment design and applicable standards, important components may include flame supervision, ignition controls, airflow proving devices, high-temperature limits, gas pressure switches, and safety shutoff valves.
Modulating gas controls can also help maintain consistent discharge temperatures during changing heating demand.
OEMs should evaluate how burner controls integrate with the equipment’s blower system, temperature sensors, and overall control architecture.
The complete safety system must be designed and tested according to applicable requirements.
Why Is Early Collaboration With a Burner Manufacturer Important?
Burner selection often becomes more complicated when it occurs late in the equipment development process.
An OEM may discover that a selected burner requires additional cabinet space, different airflow conditions, revised controls, or changes to the gas train.
Working with a burner manufacturer during initial design can help identify these issues before prototypes are built.
Midco International provides engineering assistance for OEMs developing direct-fired make-up air and process heating equipment.
Our team can help evaluate heating capacity, burner configuration, airflow requirements, combustion characteristics, and integration considerations.
Midco also offers in-house testing capabilities to support equipment development and applicable certification processes.
This collaborative approach helps OEMs make informed design decisions while reducing the potential for costly modifications.
Frequently Asked Questions About Direct-Fired Make-Up Air Burner Selection
What is the most important factor when choosing a make-up air burner?
No single factor determines the best burner. OEMs must evaluate heating capacity, airflow, pressure differential, emissions, modulation requirements, fuel type, and equipment configuration together. The selected burner must operate safely and reliably within the complete heating system.
How do I calculate the BTU requirements for a make-up air burner?
A common starting calculation is BTU/hr = 1.08 × CFM × temperature rise in degrees Fahrenheit. This estimates the useful heat required under standard air conditions. Actual burner sizing should account for air density, elevation, operating conditions, and equipment design.
Why is high turndown important for industrial make-up air systems?
High turndown allows a burner to operate across a wider range of heating demands. This can improve discharge temperature control and reduce unnecessary cycling when outdoor temperatures or ventilation requirements change.
What is the advantage of a modular direct-fired burner?
Modular burners allow OEMs to develop different burner assemblies using standardized sections. This provides flexibility for varying cabinet dimensions, heating capacities, and equipment configurations while potentially simplifying manufacturing and inventory management.
Are direct-fired make-up air burners suitable for process heating?
They can be suitable for certain industrial process heating applications, depending on required temperatures, airflow conditions, emissions, and applicable standards. OEMs should confirm that the burner and complete heating system are appropriate for the intended process.
Can Midco International help with burner testing and ANSI certification?
Yes. Midco provides engineering support, combustion testing, and assistance with applicable equipment certification requirements. OEMs can work with Midco to evaluate burner performance and integration before proceeding through the required certification process.
Choose the Right Make-Up Air Burner With Midco International
Selecting a direct-fired make-up air burner requires careful consideration of heating capacity, airflow, combustion performance, equipment configuration, and safety requirements.
For OEMs developing commercial ventilation equipment, industrial heating systems, or specialized process heating applications, the right burner can support reliable operation, flexible equipment design, and long-term performance.
Midco International provides customizable HMA direct-fired make-up air burner solutions backed by combustion engineering expertise and technical support.
Our HMA-2 and HMA-2A burner platforms offer modular construction, advanced two-stage combustion technology, and modulation capabilities for demanding OEM applications.
Contact Midco International today to discuss your make-up air burner requirements and learn how our engineering team can help you select the right combustion solution for your equipment.