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  1. #40
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    Quote Originally Posted by MicahWes View Post
    WHY is 1st stage less efficient???
    Less IR heat transfer. The heat exchanger cell is X inches in diameter. And the inducer doesn't drop in speed to meet the exact requirements of first stage, so it has a bit more excess air, cooling the flame a bit more.
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  2. #41
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    Jan 2004
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    Quote Originally Posted by Jkb79 View Post
    I guess I understand that in 1st stage that the furnace would not have the full capacity of the entire house, and I can see how if 1st stage is allowed to run for a very long time how it would be less efficant than at full fire. I guess maybee my understanding of the fire efficacy between first and second stage is incorrect. My view point on beeing able to drop the temp a degree or two because I have a 2 stage system could only come from the fact that when the furnace is in first stage it does not remove as much humidity from the air as compared to the old single stager. So if it is less efficant to have first stage on then why don't I just install a humidifier on the singlet stage furnace and keep humidity up which would allow for a degree or two drop in the stat due to the fact that the more humid air would make me feel warmer. I'm not trying to make anyone mad or anything I'm just trying to learn. Please help me to understand thanks.
    Unless its using inside combustion air, or has a leaky duct system. It doesn't remove any humidity.

    First stage aids in preventing people from feeling cool/cold drafts right after the furnace shuts off. A single stage makes many people feel cool when it shuts off since they don't feel that large volume of hot air moving anymore.
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  3. #42
    Join Date
    Oct 2009
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    Raleigh, NC
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    Is it a fact that the lower speed of my inducer fan isn't matched to the air requirements of 1st stage? I have no way of testing this, but I feel like a furnace manufacturer would design 1st stage to operate as efficiently as possible. So far, my furnace only steps up to 2nd stage when I turn the thermostat up a few degrees. I would imagine this is the case in most homes with 2-stage equipment. If anything, it seems they would let 2nd stage slide a little in engineering design.

    Also, why would I care very much about IR transfer in a warm-air furnace? Does radiant energy emitted from the HX (to the walls of the furnace, I guess?) really add much efficiency?

  4. #43
    Join Date
    Jan 2013
    Location
    Champaign Illinois
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    97
    Okay that makes sense. I find myself experiencing the draft issue when I'm watching tv. And I see the point of the inducer not slowing down to match fire rate making it a little less efficant than a variable speed inducer or a modulating inducer. However I would still contest that first stage is more efficant than 2nd. I guess the best way for me to explame myself is that, in first stage we are consuming less gas and getting less btu's. If I can maintain temp and consume less isn't that more efficant. I think of it like a heat pump. It's more efficant to run compressor till the load is to great / balance point. At wich time it is more efficant to turn the strips on. So I would think it would be better to run first stage for as long as possible. I can see how full fire is more efficant on a high load because it would satisfy the stat a lot quicker and use less gas doing so. But I can only see that situation commng about for only a couple of weeks throughout the heating season assuming the home is properly insulated.

  5. #44
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    Jul 2010
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    nebraska
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    Quote Originally Posted by MicahWes View Post
    WHY is 1st stage less efficient???
    Because the inducer does not slow at the same proportion as the reduction in gas.It will slow down but not directly proportional. You then have even more nitrogen entering the combustion chamber causing a cooler flame and less heat tranfer. IR heat transfer is over half of the BTU output so yes a reduction is a big thing.

  6. #45
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    Jan 2013
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    Champaign Illinois
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    I think I understand now, first stage is for comfort. Thanks for the input. I guess u learn something new every day.

  7. #46
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    Oct 2009
    Location
    Raleigh, NC
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    Wait, IR (as in infared radiation) is responsible for 1/2 BTU output? It has been a long time since my thermodynamics classes in college, so there is a lot I may be mistaken about, but isn't most heat transfer in a warm air furnace via conduction and convection?

  8. #47
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    Oct 2009
    Location
    Raleigh, NC
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    Wait, are you speaking of the IR radiation from the flame itself to the inside walls of the HX as opposed to the heat transfer from the HX to the airstream of the house?

  9. #48
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    Jun 2001
    Location
    Moore, Oklahoma, United States
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    I don't know how much design temp weather you have had since you installed the furance but I'd like to know how cold it actually has to get before the 2nd stage kicks in. I have a feeling a LOT of 2 stage furances are getting installed where the 2nd stage is never needed. A Smaller 1 stage furance could do the job for a lower cost while maintaining the same comfort. Sadly 2 burner furnaces are rarely installed as the primary heat source for a single family home, regardless of heating needs.

  10. #49
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    Lancaster PA
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    Quote Originally Posted by MicahWes View Post
    Wait, are you speaking of the IR radiation from the flame itself to the inside walls of the HX as opposed to the heat transfer from the HX to the airstream of the house?
    Now your catching on. Under fired your not getting the heat from the IR of the flame to the HE walls like you should.
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  11. #50
    Join Date
    Jan 2007
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    Mn the state where absolutey nothing is allowed
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    Quote Originally Posted by MicahWes View Post
    Wait, are you speaking of the IR radiation from the flame itself to the inside walls of the HX as opposed to the heat transfer from the HX to the airstream of the house?
    now your getting it, many of us have been speaking of heat-exchanger efficency. remember hot air heats the house, heat exchangers heat the air, and the fire( proper combustion, this is the only portion a combustion anayizer measures) heats the heat-exchanger.

    so physics state there is greater heat transfer when there is a greater temperature differential. therfore a more efficient furnace has a hotter fire
    my boss thinks its possible to repeal the laws of physics

  12. #51
    Join Date
    Jul 2005
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    5,380
    Quote Originally Posted by SBKold View Post
    Warm air coming from vents for longer time rather than hot air for 15mins then off back on ......off.....
    Temp rise in high vs. low doesn't typically vary by more than 5 on a properly commissioned furnace. There is less air moving in low stage though so runtime is extended vs. high stage.

  13. #52
    Join Date
    Jan 2013
    Location
    Champaign Illinois
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    97
    I do have to say that the company I used to work for on the north shore of Chicago had what I thought was a good way to size his equipment. He would size at 0 degrees. When I asked him why he did that instead of the standard -5 to -10, he asked me how often are we at -5. I thought for a Min. And said well I guess for a couple of weeks or so. He replayed, so for 2 weeks of the year the furnace will run full boar. The rest of the time it will run more efficantly than if we increased the size. ( we were installing Trane 20k BTU increments on size). For the 9 years I was with them I had 2 systems that the customer insisted that we up the size. We did what they wanted at no extra caust.

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