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Cast Iron boiler SS vent condensation?

billyboy Member Posts: 152
Am installing Burnham ESC3 CI boiler that will be heating a 79 gallon Viessman indirect tank.

Sidewall 3” SS vent pipe 40’ total length, all contained in conditioned space.

Will have condensate drain at the start of 30’ of sloped horizontal vent.

At first I will collect & measure water condensate.

Any guesses as to how much I will collect per cubic yard of NG?


  • billyboy
    billyboy Member Posts: 152
    Surface area of the SS vent pipe will be about 31.5 ft2
  • billyboy
    billyboy Member Posts: 152

    Exhaust gases
    The amount of water vapour in exhaust gas depends on the type of fuel. Complete combustion of one mol of methane (CH4) at standard conditions (absolute pressure 101.325 kPa, absolute temperature of 273.15 K) with oxygen (O2) produces two mol of water vapour: the molar mass of water vapour at standard conditions is 18.015 kg/kmol, while the molar mass of methane is 16.043 kg/kmol.
    Therefore, complete combustion of 1 kg of methane releases 2 · 18.015/16.043 = 2.25 kg of water vapour. The density of methane is 0.717 kg/m3, again at standard conditions. Consequently, the combustion of one m3 of methane releases 0.717 · 2.25 = 1.61 kg of water vapour.
    Complete combustion of one m3 of methane at standard conditions without condensation releases 35.88 MJ of energy if the starting temperature of the combustion process is 25°C and the combustion end products are cooled back to this starting temperature. However, if the combustion end products are really cooled down to 25°C, a large part of the water vapour in the exhaust flow will condense and release its vaporisation heat. With the condensation included, combustion of one m3 of methane releases 39.82 MJ of energy.
    We call the amount of energy released without condensation the inferior, net, or lower calorific value Hi of the fuel, while when the condensation energy is included we talk about the gross, superior, upper or higher calorific value Hs. For methane, the Hs is a factor 1.11 higher than the Hi. For most natural gases, the Hs is about 10% higher than the Hi.
    The heat present in the combustion end products without condensation is generally called the sensible heat. One can sort of sense the heat in the combustion end products based on the temperature. The heat resulting from condensation is called the latent heat. This heat is basically available, but it is only released by condensation.