High efficiency appliances venting requirements

Home Maintenance Questions and AnswersCategory: Furnace VentingHigh efficiency appliances venting requirements
Question by Cory

So why do high efficency appliances need to have the intake and exhaust vents installed so the terminations are the same length and so close to one another? I have not had this question answered yet and am curious. Please advise…Corry

1 Answers
Dariusz Rudnicki Staff answered 11 months ago

Hi Corry, it’s slightly beyond house maintenance advice 🙂

There are some basic requirements that apply to some high efficiency appliances utilizing exterior intake and exhaust (there are still various types and brands that allow air combustion from interior of the house … and the following would not apply).
 
Those requirements are pretty much based on fundamental laws of physics – because hot air is less dense than cold air, it rises naturally (that’s rather visual explanation … actually cold air replaces warm air …), anyway, exhaust should never be located lower than intake and its opening should be within 12″-24″ from the intake opening (those numbers might slightly vary between the manufacturers).

  • Not less than 12″ because exhaust gases are not suitable for being reused as combustion air and could be sucked back in, and
  • not more than 24″ because it would be out of so called atmospheric pressure zone (area within 12″-24″)

 
Flue gases discharged through the exhaust pipe create this zone, and help admit combustion air into the intake pipe. As far as terminations being the same length, I’m not sure if I understand … the vent and intake systems should have the same number of elbows, and approximately the same length of straight sections, but exterior terminations of both, as long as within the zone and within other manufacturer requirements (distance from the wall, from the ground, openings, etc.) don’t have to be the same length.

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