Choosing the right direct-fired make-up air burner is an important decision for original equipment manufacturers (OEMs), HVAC equipment designers, and industrial heating professionals. Burner selection affects heating capacity, combustion stability, emissions performance, equipment configuration, and long-term reliability.
Midco International has developed direct-fired make-up air burner solutions for commercial and industrial applications for decades. Two important products in its HMA burner family are the HMA-1 and HMA-2A. While both are designed to heat moving air directly, they offer different combustion technologies, operating capabilities, and application considerations.
The primary difference is that the HMA-1 is Midco’s established legacy burner, while the HMA-2A uses advanced two-stage combustion technology to provide greater heating capacity, lower emissions, and a wider operating range.
For new equipment designs, Midco recommends the HMA-2A product family. The HMA-1 remains relevant for manufacturers and facilities supporting existing installations.
Understanding these differences can help OEMs select an appropriate burner for make-up air equipment, industrial ventilation systems, and specialized process heating applications.
What Is the Midco HMA-1 Burner?
The Midco HMA-1 is a direct-fired gas burner developed for commercial and industrial make-up air heating applications. It is designed to heat incoming air used to replace air removed through ventilation and exhaust systems.
The HMA-1 uses a straightforward combustion arrangement in which natural gas or propane is delivered to the burner ports at low pressure. Specially designed burner baffles allow combustion air to mix with the fuel as air passes through the burner assembly.
This design supports dependable heating performance across a range of operating conditions.
The HMA-1 provides heating capacities up to approximately 550,000 BTU/hr per linear foot under standard published conditions. Higher capacities may be possible for certain applications with factory review.
Its modular construction allows manufacturers to assemble burner configurations using straight, elbow, tee, and back-inlet sections.
The HMA-1 has been used in applications such as industrial make-up air equipment, grain drying, process drying, and heated air curtains.
Although the HMA-1 remains important for existing customers, Midco directs new applications toward the HMA-2A family.
What Is the Midco HMA-2A Burner?
The Midco HMA-2A represents a newer approach to direct-fired make-up air combustion.
Rather than relying on the original HMA combustion arrangement, the HMA-2A incorporates Midco’s patented two-stage combustion technology.
This design creates two separate flames within the burner combustion zone, helping produce a shorter, more stable flame while reducing carbon monoxide (CO) and nitrogen dioxide (NO₂) emissions.
The HMA-2A also provides greater heating capacity and flexibility across a wider range of airflow conditions.
Published HMA-2A capabilities include heating capacities up to 750,000 BTU/hr per linear foot, differential pressures from approximately 0.05 to 1.4 inches water column, and air velocities from approximately 800 to 4,000 feet per minute.
With suitable modulation controls and gas valve components, the HMA-2A can achieve turndown ratios of approximately 30:1.
These characteristics make the HMA-2A particularly useful for OEMs developing new make-up air equipment, industrial ventilation systems, spray booths, and process heating applications.
HMA-1 vs. HMA-2A: Key Differences
| Feature | Midco HMA-1 | Midco HMA-2A |
|---|---|---|
| Product positioning | Existing installations and customers | Recommended for new applications |
| Combustion technology | Original HMA combustion design | Advanced two-stage combustion |
| Published heating capacity | Up to 550,000 BTU/hr per linear foot | Up to 750,000 BTU/hr per linear foot |
| Turndown capability | Up to 30:1 | Up to 30:1 with appropriate controls |
| Emissions | Dependent on installation and operating conditions | Two-stage design supports reduced CO and NO₂ |
| Modular configurations | Yes | Yes |
| Fuel options | Natural gas and propane | Natural gas, propane, and factory-reviewed butane applications |
| Typical selection | Supporting existing equipment | New OEM make-up air and process heating designs |
Both burners require proper airflow, controls, installation, and combustion testing. Published ratings do not guarantee identical performance in every equipment configuration.
How Does Two-Stage Combustion Make the HMA-2A Different?
One of the most significant improvements in the HMA-2A is its two-stage combustion process.
In the original HMA-1 design, fuel is introduced through burner ports and mixed with combustion air passing through the burner baffles.
The HMA-2A uses two separate combustion stages to improve control over flame development.
This arrangement produces a shorter, more stable flame and helps reduce emissions over a wider operating range.
For OEMs, improved flame stability can provide advantages when designing equipment with varying airflow conditions or limited combustion chamber space.
Reduced CO and NO₂ emissions are particularly important in direct-fired heating applications because combustion products enter the heated air stream.
The HMA-2A’s combustion technology helps manufacturers address these concerns while supporting the development of higher-capacity heating equipment.
Which Burner Offers Greater Heating Capacity?
Heating capacity is an important factor when selecting a burner for industrial ventilation or make-up air equipment.
The HMA-1 provides published capacities up to 550,000 BTU/hr per linear foot.
The HMA-2A increases this published capacity to 750,000 BTU/hr per linear foot under appropriate operating conditions.
For example, a burner assembly with four linear feet of active burner length could have a nominal capacity of approximately 2.2 million BTU/hr using the HMA-1 rating or 3 million BTU/hr using the HMA-2A rating.
Actual available capacity depends on burner configuration, airflow, pressure differential, fuel supply, and emissions requirements.
For manufacturers designing high-capacity make-up air equipment, the HMA-2A may provide additional flexibility without requiring as much burner length for a given nominal heating load.
However, capacity should never be the only selection factor. Combustion stability, airflow, emissions, and the complete equipment design must also be evaluated.
How Do Airflow and Pressure Requirements Affect Burner Selection?
Direct-fired burners depend on proper airflow to support combustion and distribute heat throughout the equipment.
The burner profile, air velocity, pressure differential, and blower arrangement all influence performance.
The HMA-2A is designed to operate across a published differential pressure range of approximately 0.05 to 1.4 inches water column, corresponding to air velocities of approximately 800 to 4,000 feet per minute.
This operating flexibility can be valuable for OEMs developing equipment with different airflow requirements or cabinet configurations.
The HMA-1 also requires carefully controlled airflow, but its operating limits should be evaluated using the appropriate HMA-1 documentation rather than assuming the same conditions apply.
For either burner, improper airflow distribution can lead to unstable combustion, uneven discharge temperatures, or increased emissions.
Midco recommends evaluating burner placement and profile dimensions as part of the complete equipment design.
Does the HMA-2A Provide Better Emissions Performance?
The HMA-2A was developed in part to improve combustion performance and reduce emissions compared with earlier burner technology.
Its two-stage combustion arrangement supports lower carbon monoxide and nitrogen dioxide emissions while allowing greater flexibility in heating capacity and operating conditions.
This is especially important for OEMs manufacturing equipment that must satisfy applicable ANSI requirements.
Depending on the intended application, these may include ANSI Z83.4 for non-recirculating direct-fired heating equipment, ANSI Z83.18 for recirculating direct-fired equipment, and ANSI Z83.25 for qualifying process air heaters.
The HMA-2A’s design can help OEMs address the combustion performance requirements associated with these standards.
However, certification applies to the complete heating appliance, not simply the burner. Actual emissions must be verified through appropriate testing under the equipment’s intended operating conditions.
Can Both HMA Burners Be Customized for Different Equipment Designs?
Yes. Both the HMA-1 and HMA-2A use modular construction to support different heating capacities and physical equipment configurations.
Available burner components include straight sections, elbows, tees, and inlet arrangements.
This allows manufacturers to create burner assemblies suited to different cabinet dimensions, duct layouts, and heating requirements.
For OEMs producing multiple equipment models, modular construction can simplify burner integration and reduce the need for completely different burner designs.
The HMA-2A combines this modular flexibility with newer combustion technology, making it particularly attractive for manufacturers developing new products.
Midco also provides engineering drawings, component information, and technical support to help manufacturers evaluate burner configurations.
When Does the HMA-1 Still Make Sense?
Although the HMA-2A is recommended for new applications, the HMA-1 remains relevant for existing equipment.
Manufacturers and facility operators may need HMA-1 components, maintenance information, replacement parts, or technical assistance to support installed systems.
For equipment originally engineered around the HMA-1, maintaining the existing burner configuration may be appropriate when the system continues to operate safely and meets applicable requirements.
Replacing an HMA-1 with an HMA-2A should not be treated as a simple interchangeable upgrade.
Differences in combustion technology, burner geometry, airflow requirements, controls, and certification considerations may require engineering modifications.
Midco can help evaluate existing equipment and determine whether continued HMA-1 support or a redesigned HMA-2A configuration is more appropriate.
Why Is the HMA-2A Recommended for New OEM Applications?
For manufacturers developing new commercial or industrial heating equipment, the HMA-2A offers several important advantages.
Its higher published heating capacity can support equipment requiring substantial heat input, while its two-stage combustion technology provides improved flame stability and reduced emissions.
The wider operating range gives engineers more flexibility when designing burner profiles and airflow arrangements.
Modular construction also allows the burner to be configured for different equipment dimensions and heating requirements.
These characteristics make the HMA-2A suitable for new make-up air units, automotive spray booths, industrial ventilation equipment, and specialized process heating applications.
For OEMs focused on product development, emissions performance, and flexible equipment integration, the HMA-2A is generally the preferred starting point.
Frequently Asked Questions About HMA-1 and HMA-2A Burners
Is the Midco HMA-1 burner discontinued?
Midco currently provides HMA-1 information for existing customers and directs all new applications to the HMA-2A product family. OEMs needing replacement components or support for an existing HMA-1 installation should contact Midco to confirm availability and compatibility.
What is the biggest difference between HMA-1 and HMA-2A burners?
The biggest difference is combustion technology. The HMA-1 uses Midco’s original direct-fired combustion design, while the HMA-2A incorporates two-stage combustion to improve flame stability, reduce emissions, and support a wider operating range.
Does the HMA-2A have a higher BTU capacity than the HMA-1?
Yes. Midco publishes a capacity of up to 750,000 BTU/hr per linear foot for the HMA-2A, compared with 550,000 BTU/hr per linear foot for the HMA-1 under their respective rated conditions.
Can an HMA-2A replace an existing HMA-1 burner?
A replacement may be possible, but it requires engineering review. Differences in burner configuration, airflow, controls, and equipment certification must be considered before modifying an existing heating system.
Which Midco burner is better for new make-up air equipment?
Midco recommends the HMA-2A family for new applications. Its two-stage combustion technology, higher capacity, modular construction, and operating flexibility make it a strong option for modern OEM equipment designs.
Can HMA-1 and HMA-2A burners operate on propane?
Both burner families support appropriate propane applications. Fuel-specific components, gas pressure requirements, and burner configurations must be verified with Midco before installation or conversion.
Does Midco International provide engineering assistance for HMA burners?
Yes. Midco International provides technical information, engineering assistance, and burner integration support for OEMs developing make-up air and industrial heating equipment.
Choose the Right HMA Burner With Midco International
Both the HMA-1 and HMA-2A have important roles within Midco International’s direct-fired make-up air burner product family.
The HMA-1 remains an established solution for existing installations, while the HMA-2A offers advanced combustion technology, greater heating capacity, and additional operating flexibility for new equipment designs.
For OEMs developing commercial ventilation systems, industrial make-up air units, spray booths, or process heating equipment, selecting the correct burner requires evaluating heating capacity, airflow, emissions, controls, and application-specific requirements.
Midco International combines decades of combustion engineering experience with modular burner technology and technical support to help manufacturers develop reliable heating solutions.
Contact Midco International today to discuss your HMA burner requirements, obtain technical specifications, or explore the HMA-2A product family for your next OEM heating project.