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Principles of Make-Up Air

How a make-up air system works

Make up air systems replace stale air exhausted from industrial and commercial buildings with fresh, heated outdoor air, maintaining a constant leaving-air temperature regardless of the incoming, outdoor-air temperature.

We offer a direct-fired burner with a turndown ratio of 30:1 that is 100% efficient - all the heat goes directly into the airstream. The high turndown capability allows the flame to adjust to wide, outdoor-air temperature swings throughout heating season. For example, a unit with a maximum temperature rise of 90 degrees in the winter can adjust down to as little as a 3 degree temperature rise for milder spring and fall weather.

Make-up air systems replenish equal amounts of fresh air for every cubic foot of air exhausted. Other types of air-handling systems temper air, but simply do not offer both the efficiency in operating costs and in fuel consumption while providing comfort that direct-fired systems deliver. And, a direct-fired system installs easily - no vents, flues and chimneys, which means less maintenance.

Finally, make-up air systems solve five major ventilating problems:

  1. maintains comfort
  2. controls infiltration
  3. replaces stale air with fresh air
  4. prevents negative air pressure
  5. reduces cold and hot spots

Is safety a concern?

Direct-fired, make-up air is the safe and efficient way to introduce fresh, make-up air continuously. Mixing fresh air with combustion products concern some. In fact, contaminant levels from direct-fired heaters are not only well below recommended, safe levels, but the constant flow-and-exchange of fresh air removes contaminants well before any significant levels can accumulate

The Public Health Service and Occupational Safety Health Agency(OSHA) have set contaminamt-threshold limits for human exposure of carbon monoxide, nitrogen dioxide, and carbon dioxide - eight hours per day, 40 hours per week without a significant health hazard.

The chart below compares the current limits established by OSHA with the combustion by-products of our direct fired unit as tested by ETL - an independent testing agency.

Contaminants Limits (ppm) Direct Fired Unit (ppm)
carbon monoxide 35 5
nitrogen dioxide 1 0.5
carbon dioxide 5,000 4,000