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  1. #1
    Join Date
    Aug 2009
    Location
    southeastern wisconsin
    Posts
    33

    The effects of no intake pipe on 90% furnace

    What are the effects of not installing the combustion intake pipe or baffle on a 90% efficient furnace? My guess, is it would burn hotter and cause the heat exchanger to wear out 10 years earlier then it should. Just looking for advice from someone with a little more experience.

  2. #2
    Join Date
    Jul 2006
    Posts
    6,458
    I dont like them and do not use them if i dont have to. Most are 1 or 2 pipe.
    I think its bad to bring cold outside air in and dump it on a burner myself.
    Wait till the combustion guys get here we may both learn something.
    You sure are cocky for a starving pilgrim.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,761
    Won't cause it to harm the HX if its been set up right.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Aug 2009
    Location
    southeastern wisconsin
    Posts
    33
    This Furnace was a Payne Don't have model and serial #'s but it had holes for the intake I just thought someone was to cheap or to lazy to run the extra pvc pipe.

  5. #5
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    1,990
    It is going to depend on the manufacturer, some will require it others don't. I believe that some brands it even varies model to model.

    Dumping cold air onto a burner isn't going to make any difference, the burner just wants the O2 it doesn't care about the temp.

    It also depend on where the unit is located. If it is in the conditioned space why use air that you have aready paid to heat just to run across burners and blow outside, only to be replaced by cold air coming in around doors and windows. If it is in anywhere outside of the conditioned space the air intake won't make much difference, unless it is in a contaminated area.

  6. #6
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,142

    Cool

    In a small CAZ, it can depressurize the room and backdraft a gas WH. It sucks air out of the house causing some passive infiltration.

  7. #7
    Join Date
    Aug 2009
    Location
    southeastern wisconsin
    Posts
    33
    Nothing is wrong with the heat exchanger I just thought it needed intake pipe and baffle. It was a new install and I have never seen just a exhaust pipe and no intake pipe. I'm still new in the field.

  8. #8
    Join Date
    Aug 2009
    Location
    southeastern wisconsin
    Posts
    33
    This furnace didn't have a baffle or intake pipe to control the oxygen. My question is if it has too much oxygen will that cause it to run not as efficient?

  9. #9
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    1,990
    Excess air in a burner will lower the efficency. The Nitrogen in the air will soak up some of the heat in the HX. If you run a Combustion Analysis you can tweak the air/fuel ratio and gain efficency by controling excess air.

  10. #10
    Join Date
    Jul 2008
    Location
    Mid Michigan
    Posts
    319
    It will be less efficent by a few percent because it is useing indoor air for combustion instead of outdoor air.

    I have found wood stacked under the intake for 90% furnace.

    It snowed and they had no heat.

    I found the furnaces sealed burner cabinet full of snow.

    I had to clean out the snow and replace the units 3 wire pilot (Carrier) worked like a champ after.
    Waddya mean don't thaw out the frig with a knive?

  11. #11
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,842
    We only vent with two pipes, period. Several reasons the main being we want the combustion air coming from the outside so that it is in the same pressure zone as the exhaust and not taking air from the interior causing negative pressure and air infiltration.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  12. #12
    Join Date
    Jul 2006
    Posts
    6,458
    Quote Originally Posted by kls-ccc View Post
    Excess air in a burner will lower the efficency. The Nitrogen in the air will soak up some of the heat in the HX. If you run a Combustion Analysis you can tweak the air/fuel ratio and gain efficency by controling excess air.
    By adjusting the secondary air ports correct?
    I will have to investigate to see if efficiency is lost on my units, i know it depends on brand etc.
    Around here there are very few houses tight enough to worry about air infiltration. I only wish it were a problem in my house,leaks like a sieve
    You sure are cocky for a starving pilgrim.

  13. #13
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    4,927
    ...if the furnace is in a big open basement, your fine. If it's in a closet, or anything considered to be a "confined space", then you need the 2 pipe.

    Hearthman: If the space is small enough to backdraft a water heater, then the water heater should have a C/A anyways .
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

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