Heating, Ventilation and Air Conditioning (HVAC)

• What is the best way to determine if the heat exchanger of a standard furnace has a failure?

  • The difficult part of evaluating heat exchangers is the fact that only 15–20% of a standard heat exchanger is visible. The best way to determine if you have a failed heat exchanger is to do the following
  • Turn the unit on by raising the thermostat. This should cause the atmospheric burners to come on. Look at the flame pattern before the fan comes on. There should be bluish flames with a small amount of orange/yellow at the tips, and they should be erect or vertical.
  • Look at the burner flames again when the fan comes on. There should be no difference in the flame pattern. If there is, then it suggests that the fan is forcing air from the house side into the path of the flame, and forcing exhaust through a crack or hole in the heat exchanger. This occurs because the fan will pressurize the heat exchanger from the house air side.
  • Although there are other methods to determine a failure, watching for a distorted flame pattern, while not perfect, is a very dependable method.
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• How can you conclusively determine if a steam boiler is good or bad?
  • You must first develop pressure in the system before steam will be forced through a crack. Steam boilers do not develop pressure until air is evacuated from all of the radiators and they are filled with steam. When the radiators are filled, pressure builds up in the system. (From a cold start, this usually takes 40–70 minutes to develop, depending on the size of the system and size of the burner).
  • Residential units typically operate with 2–5 psi as the limit. Commercial steam boilers may operate with 80–100 pounds or more, depending on the application.
  • The limit control and the pressure gauge are usually located at the top of the boiler.
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