SylvanLMP
Harold, the NFPA (54) is not wrong either is ANSI 223.1 Or the AGA National Fuel code when they specify chimney height off the roof.
What these code bodies do specify “chimney termination is based upon residential or low heat utilization’s and they shall extend at least 3 ft above the highest point where it passes through a roof of a building and at least 2 ft higher then any portion within a horizontal distance of 10 ft ” SEE National fuel code (NFPA 54) Article 7.5.2a
You also must take into consideration a “plumbing” vent pipe does not have the “draft diverter” of the gas counter parts to prevent spillage and the plumbing vent is working 24-7 unlike a gas/oil / coal / wood appliance that fires part time.
So the down draft condition is not as common as a much larger opening of a chimney/flue.
The plumbing vent is subjected to hoarfrost and negative pressures when a fixture is used.
When the waste water is flowing down a drain does cause a slight back pressure on the venting system (especially on undersized venting).
The plumbing vent system is designed to be able to function without any mechanical means or special draft hoods.
The cold in coming air is pulled into the Fresh Air inlet (FAI) located within 4 feet of the building trap and it sized at half the size of the building house drain Or 3″ which ever is larger and is it located 6″ above grade.
Then as this cold air picks up the warm sewer gases it causes a natural draft up to the roof terminals.
Knowing sewer gases can be carcinogenic and flammable is the reason the codes do specify the horizontal distance from any window or door or adjoining building AND that is why promenade roofs and roofs OTHER then weather protection only have these vent terminals extend a minimum of 7 feet and 2′ on weather protection roofs only.
Harold I am a federally certified low pressure boiler inspector (ASME and NBBI) and unfired pressure vessel inspector PLUS a member of the NFPA as I do have a Master fire suppression piping contractors license.
Granted I do not follow up as much as I would like on NFPA 54 as lately I have been studying NFPA 13 (sprinkler systems).
Lots of changes on designs and conflicts with other NFPA publications, like inspectors test station locations.
These is so much knowledge to learn out there and so little time.
Rather then discuss this on here your more then welcome to bring this topic up for discussion on the PIPDL list where we can get other professionals involved in a round table heated discussion.
Harold, as always a real pleasure reading your postings.
