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Concentric Venting

paule Member Posts: 17
For a mod-con boiler (a Heat Transfer Elite), are there are disadvantages to using a concentric vent pipe?  Are there any advantages (other than aesthetics)?




  • Tim McElwain
    Tim McElwain Member Posts: 4,554
    The advantage is that

    you are preheating the air for combustion before introducing it to the combustion process. That will help the overall efficiency and is the best way to go.
  • Lance
    Lance Member Posts: 241
    Concentric vent

    Contrary to popular thinking fuel combustion does not care how cold or hot the O2 is unless it involves vaporation of a fuel and that may not be affected unless extreme conditions apply. The only disadvantage I see in concentric venting is repairing leaks or clogs as some concentric assemblies do not allow for maintenance. Usually my concern is will I be able to fit a larger hole vs a rectangle or two smaller holes in my application.
  • Tim McElwain
    Tim McElwain Member Posts: 4,554
    After 50 years of working

    with both natural gas and propane it has been my experience that low temperatures related to air for combustion can have an affect on the combustion process. This is why the old timers used to hang 200 watt light bulbs in boiler rooms to create some heat when air for combustion was being brought directly from out doors.

    There have been many debates concerning this over the years but experience to my way of thinking is the best teacher. Hence if you can find a way to heat the air before it enters the combustion process then do so.

    Keep in mind also that some gas valves are only rated to operate from zero to 150°F. So if the room gets down that low or close to it the valve may not open.

    I have on purpose actually gone and done combustion tests on equipment on very cold days just to see what affect it would have on the overall combustion process. This is equipment that had previously been set up with normal say 60°F room air temperatures. There was a definite difference particularly with the dilution air being pulled into the draft hood. In a couple of cases I actually saw a curtain effect take place on the system.
  • Henry
    Henry Member Posts: 995
    Cold air

    Pre heating combustion air is very common in large power plants. It also reduces the CO and NO levels. However high flame temperatures actualy increase NO emmissions. The new Bryan condensing boiler condenses even at 180F temperatures because it reuses some of the combustion gases to pre heat the combustion air.

    Very cold combustion air in seperate combustion, will actualy upset the balance with fixed orifice premix burners as the Oxygen levels are higher in cold dense air. This is the reason for having an intercooler on turbocharged hotrods. The intercooler cools the air to get more oxygen to the fuel.
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