Boiler Room Combustion Air Requirements

| Edward McKellar

Spring is the time of year that many plants begin planning and conducting annual maintenance on installed boilers and burners. Boiler combustion tuning is important to keep boilers performing their best through the changes in seasons. All combustion relies on fuel, heat, and air. It’s not often realized that combustion is no more than just a chemical reaction. Air itself generally consists of about 78% Nitrogen and 21% Oxygen, and a small percentage of other gases. The starting point of any combustion process is a healthy supply of fresh air.

Mechanical rooms and boiler plants are engineered to meet these make-up air requirements by having proper ventilation along with maintaining the correct free space. This means that using a boiler room for storage is not among the best practice. Boilers that are being starved of air requirements will rapidly develop combustion problems and can lead to serious fireside problems along with increased fuel consumption.

Combustion Air inside a boiler plant is critical. Boilers rely on air for continued operations.
A 600 Horsepower Cleaver-Brooks Boiler relies on a healthy dose of combustion air for reliable operations.

A boiler room requires proper ventilation as defined by NFPA 54. The National Fire Protection Association code recommends at least two openings within a boiler room to provide sufficient flow through. These openings should be directly connected to the outdoors and ideally on each end of the boiler. The height of installed vents and louvers is an important consideration as well. These vents should be placed accordingly to allow incoming air and existing air to mix and acclimate with one another.

Oftentimes these louvers use a grating or expanded metal covering to provide protection. These openings should never be covered with a fine mesh as they will create flow-through problems. Ventilation openings should be a daily visual check to ensure the adequate space is clear for proper boiler room ventilation.

Many plants oversize ventilation requirements and it’s not uncommon to see where these louvers are intentionally blocked to cut down on drafts inside the boiler room. Oversizing the air requirements may ensure that combustion air is met, however it can cause the boiler room to lose heat more rapidly in off cycles. A calculated air requirement within a well-engineered system is a better practice to achieve the best boiler room efficiency.

Using a boiler room for storage can hinder combustion air supply
900 HP Superior Boiler providing central plant steam

Optimal combustion relies on an adequate supply of air inside the boiler room.

When boiler rooms are sized and air requirements are determined air flow-through, velocity, and square footage of the space are all determinants.

The industry standard for determining the amount of required air is as follows:

  • Combustion Air = Rated Boiler Horsepower x 8 CFM/HP
  • Ventilation Air = Maximum Boiler Horsepower x 2 CFM/HP
  • Total Recommended Air = 10 CFM/BHP*
    • * Add 3% for every 1000 feet of elevation.

Total required air Example: 500 HP x 10 = 5000 CFM

These are general calculations along with some national code requirements and boiler rooms should always be properly engineered with acknowledgment of any local codes and other jurisdictional requirements.

Proper air requirements are critical for efficient and long-lasting combustion systems. Apply these principles to ensure your boiler rooms are operating at their peak.

Contact Power Mechanical Inc.. today for more information on leveraging your scheduled maintenance periods for combustion tuning and boiler room design. With over 40 years of service in the commercial and industrial boiler rental industry, our expertise in boiler/ burner tuning can get your facility to peak performance. 1-877-764-7832

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