Tommy Mac Discussions Forums Fix-it Forum: Home Improvement & Do It Yourself Repair Forum I really don’t understand the workings of this furnace…

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    • #48523

      Hi all, lets see if I can explain this where it will make some sense. I have an Armstrong Category 4 forced air furnace, model EG6E100DC2018. It is 100,000 BTUs.

      It sits in the exact middle of the basement on one side. There is 2.5” PVC that comes out of the furnace for 18”, goes up for 30”, across the basement for 14ft and then has a 9” ‘S’ that leads out the window.

      There is also a 4” PVC that comes out of the furnace for 5”, goes up 34”, across for 12ft out the window. It also have a PVC tube that runs across the floor to the sump hole for the condensation.

      When the furnace comes on, there is a small motor that starts and runs 1-2 minutes, then the ignition fires up and it does its heating thing, about half way through, the first motor shuts off. All the time the first motor is running the 4” PVC is expelling air that looks like the dryer vent!!!!!

      Okay, so what I question,
      1. I can understand the motor coming on to expel the carbon monoxide, but why does it continue running through ½ the cycle?
      2. All that heat that is going out – shouldn’t that be coming into my house instead of going out?
      3. What is the 2½” PVC for? Fresh air? Well, that sure doesn’t make a whole heck of a lot of sense when it is 15 below outside. Take an awful lot of fuel to heat that up to 65-70 degrees…

      This just can’t be right, can it?

      Any info is much appreciated and I thank you in advance.
      Hope you all have a wonderful Thanksgiving!!

      Moderator – Construction Project Blog

      Some have better luck next time around,
      some don’t, and some don’t even try.

    • #254464

      1)The motor supplies fresh air to the burners. It comes on before the burners light to purge any potential gas build up in the furnace to prevent explosion. The motor runs as long as the burners are lit to supply fresh air. It shuts off after “1/2 the cycle” and the furnace blower (circulation) fan continues to run to circulate the remaining hot air from the furnace to the house.
      2) You have a high efficiency furnace – probably 93 to 94%. That other 7 to 6% of warm, moist combustion products has to be expelled to the outside. If your furnace was 100% efficient there would be no exhaust – but there are no furnaces on the market like that. Still, it is much, much better than the older 80% efficient furnaces that put 20% waste up the chimney.
      3)Believe it or not, it makes no difference if your furnace draws the combustion air from your warm basement or from the -15 degrees outside. If the air was drawn from the warm (65 degree) basement, it would have to be replaced by air coming into the house from somewhere else. That replacement air would be from the outside and would also be at -15 degrees, and would have to be heated up anyway. In todays tigh houses, the combustion vent direct from the outside prevents the furnace from starving for air, and also helps to prevent cold drafts from air leaking in.
      Hoped this helps. Good to hear from you on this board. I haven’t had much chance to participate lately.
      Good Luck!

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