Heating and combustion

Is Measuring Draft Important?

The pressure of  the  gases  in  the  stack  must  be  carefully  controlled  to  ensure  that  all  the  gases  of  combustion  are  removed from the combustion zone at the correct rate. This draft pressure can be positive or negative depending of the boiler design: natural draft, balance draft, and forced draft boilers are the most commonly used in the industry.

Monitoring draft is important not only to increase combustion efficiency, but also to maintain SAFE conditions. Low draft pressures create build-ups of highly toxic gases such as carbon monoxide and highly explosive gases. These build ups may take place in the combustion chamber or may even be ventilated indoors creating the risk of injury and death. Conversely, extremely high draft pressures can cause unwanted turbulences in the system preventing complete combustion. Unwanted high draft pressures tend to damage the combustion chamber and heat exchanger material by causing flame impingement.

The following operating difficulties can result from uncontrolled draft:

- Poor combustion efficiency

- Pilot / Main Flame fails to light or is unstable, causing shutdowns

- Soot accumulations due to varying fuel-air ratio

The draft regulator (barometric damper) is located on the stack, is closed when the burner is off but opens automatically to pull air into the boiler when the burner is turned on.  Accumulated soot and rattling are signs that the draft regulator  needs  to  be  adjusted.  Too much air in the chimney wastes heat; too little air wastes fuel by failing to burn it  completely. Testing Draft with our  combustion analyzer ensures the system has the proper amount of air for the system to run safely and efficiently.



Type of Heating System          Overfire Draft                                                       Stack Draft

Oil, conventional                        -0.025 to -0.05 mbar / -.01 to -.02 inH2O             -0.05 to -0.124 mbar / -.02 to -.05 inH2O

Gas, conventional                      N/A                                                                       -0.05 to -0.01 mbar / -.02 to -.04 inH2O


typical airflow

Instrumentation Solution

All of our HVAC Combustion Analyzers are equipped to MEASURE DRAFT AUTOMATICALLY.  Since  Draft  should  be  the  1st  parameter  tested  during  analysis,  our  analyzes  are  equipped  with  a  DUAL  Hoses  probe  allowing  the  user  to  automatically  test  Draft  and  Gas  Analysis  without  having  to  continously remove / reinstall the probe into the stack. Most competitors use a single hose system that can be time consuming to test.