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Combustion Air Fan & Efficiency

In order for your boiler to operate at peak efficiency, it is important that the correct balance of fuel and combustion air is achieved. Air and fuel ratios are controlled through linkages, fans, dampers and the increase or decrease of gas pressure. Gas pressure is controlled through a pressure regulator and a fan controls the volume of combustion air.
If there are any problems with the fan, more energy may be introduced into the system, causing decreased efficiency. To help ensure that your equipment is running at its peak performance, please review the common fan problems below.

Fan Capacity/Pressure is Below Rating:

  1. Dampers or variable inlet vanes are not adjusted properly

  2. Fan inlet or outlet conditions are impaired

  3. Multiple air leaks within the system

  4. Damage sustained to the blower wheel

  5. Direction of rotation is incorrect


Fan Vibration:

  1. Worn bearings

  2. Unstable foundation

  3. Foreign material in the fan causing an imbalance

  4. Misalignment of bearings, couplings, wheel or v-belt drive

  5. Damaged wheel or motor

  6. Bent shaft

  7. Worn coupling

  8. Loose dampers or variable inlet vanes

  9. Speed too high or incorrect fan rotation

  10. Vibration to fan transmitted from another source

  11. Uneven blade wear

  12. Loose or broken bolts or set screws


Overheated Bearings:

  1. Improper lubrication

  2. Poor alignment

  3. Damaged wheel or driver

  4. Bent shaft

  5. Abnormal end thrust

  6. Dirt in bearings

  7. Improper belt tension


Overload on Driver:

  1. Speed too high

  2. Direction of rotation is incorrect

  3. Bent shaft

  4. Poor alignment

  5. Improper lubrication

  6. Wheel wedging or binding on fan housing

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Freeze Protection Recommendations



The winter season is here and for many users affected by freezing temperatures it is critical that the boiler unit is properly protected. Nationwide Boiler recommends the following in order to ensure that your unit continues to operate while facing freezing conditions.

  1. Enclose both the front and rear of the boiler area and use an external heat source to minimize freezing conditions.

  2. Install heat tracing with insulation to protect exposed stagnant water lines.

  3. Utilize an appropriate heat tracing method (electric or steam tracing) to all of your main lines and piping components. This includes the following lines which should be heat traced regardless if the boiler is in operation or not (in freezing conditions): sensing lines (steam drum to CMR, high steam and steam gauge), auxiliary low-water-cut-off, water column and level control blowdown. Depending on the length of piping runs, the main and continuous blowdown should also be heat traced.

  4. In addition to heat tracing on stagnant sensing lines, drain the lines and fill them with a 50/50 (water/glycol) solution, making sure to re-connect the line.

  5. When an extended boiler down time is expected, completely drain the boiler and stagnant water lines.


The above are recommendations, however, use sound engineering judgment calls when there are concerns of possible freeze damage to the equipment. Call us if you have any further questions at 1-800-227-1966.

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