Results 1 to 7 of 7
  1. #1
    Join Date
    Jun 2004
    Is there a gas furnace, around 100,000 BTUs, that has an adjustable combustion air intake? My current, rapidly aging furnace has a large opening that most likely allows more combustion air than is necessary. I'm seeking a new furnace that will allow the installer to adjust the combustion mixture for maximum efficiency.

  2. #2

    I have just read some of your other posts. It kind of seems as though you are playing around with your furnace. By adjusting the gas pressure by the air flow and some other things. you stated your furnace is only 10 years old. gas is not something to play with and neither is your furnace especiall if you have no clue. Yo are coming here getting various replies and then opening another thread after you go try what you have been told. Please call a pro before you get hurt or kill someone. Please do that. I dont understand what you are trying to accomplish here by messing with something that could and will kill you if not done professionaly. Guy's please read his other posts.

  3. #3
    Join Date
    Jun 2004
    Thanks for you reply, 9mmnow. I'm sorry if my questions bother you. What I am trying to do is understand how the newer, high efficiency furnaces are able to deliver on their "advertized" promises. The gas pressure issue is how the Amana GCVA furnace manages two heating levels. The high level is at 3.5" W.C. while the low heating stage is at 1.9" W.C. Now that begs the question if one lowers the amount of natural gas in the combustion chamber, how do they lower the oxygen so the combustion efficiency is maintained? Does the inducer slow down and draw in less air? Today's furnace choices are not simple. Each manufacturer has their own way to make it "work". As an informed consumer, I want to understand the ways multistaging is done and what ways may be better, so I ask questions.

  4. #4
    Join Date
    Jul 2002
    Zelienople, Pa
    Does the inducer slow down and draw in less air?

    How tall are you Private???!!!!

  5. #5


    As 9mmnow said get a professional to look at the furnace if you want more efficiency out of your 10 yr old furnace get someone to set the system up with a combustion analyzer. That is the only way to get the proper air to gas mixture out of the furnace that you have. Just because you have a large combustion air louver doesn't mean that your furnace is using any or all of it. As a professional I wouldn't attempt to set the gas to air mixture without an analyzer and neither should a homeowner. We just want to protect you and your family.

  6. #6
    Join Date
    Jun 2004
    Thank you for your sincere concern, Paul. I'm not messing around with this furnace because it's too old and a new furnace is a much more cost-effective way to go. But I am getting a good understanding of furnace technology with which to ask intelligent questions of HVAC companies when they give me estimates.

  7. #7
    Join Date
    Apr 2004
    There is a lot of engineering that goes into a 2 stage unit that is not considered in a single stage design of older furnaces. The limit may be located in a different spot, water management is an issue as are flame efficiency issues. Among others. Generally the air fuel mix is controlled by a two speed inducer as well which is precicely tapped in the correct point in the windings to provide the correct mix.

    Combustion air is crucial to any furnace by suggesting to limit the combustion air you risk improper flame at the minimum and a real portential fire hazzard.

    You are not going to change the efficiency by adding low fire, 92% is 92% thats it, no ifs ands or buts about it and the heat required to heat your home is the same regardless of the output. Your furnace was and is desinged to cycle on a thermostat not vary the output to different loads by changing firing rate. If you house calls for 50,000 in an hour then your furnace will run about half the time. Staging is comfort related only, not efficiency related.

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