How does a modulating furnace modulate? - Page 2
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  1. #14
    Join Date
    Apr 2010
    Location
    Minnesota
    Posts
    515
    Of course the best way would be to put the correct communicating stat with the furnace. That's how you maintain perfect temperature, which is the whole point of a modulating furnace.

    If you must use a binary on/off stat, Tranes work like this:
    When W1 calls, the unit goes to low fire, 40%, and stays there until the call satisfies. If it's really cold out, W1 cannot satisfy the call, then W2 second stage also calls. This starts a "ramp up" routine that increases output by 3% every minute(20 minutes until full output) If at any time W2 call drops out, it immediately goes back to 40%. The main blower fan matches speed to the burner output to maintain fairly consistent temp rise.

  2. #15
    Join Date
    Feb 2008
    Posts
    30
    The Trane logic with the generic 2 stage T-stat sounds like just what I am looking for and my 3M stat does control 2 stages of heat and cool. I am in MD so winter temps can vary widely and there are many days when I could see the heater never needing anything more than the W1 40% and only on the some of the colder days does my current unit run up near 20 minutes. I'll have to put Trane on my list to look at.

    I also like the Yorks but am a little leery of the "algorhythm". In practice it might not be all that different from what you describe the Trane doing but there is no way to know. I have looked at the York literature and there is no provision to take a W2 input and use that to tweak the logic. Seems to me the way Trane does it is better.

    Quote Originally Posted by dunkman View Post
    Of course the best way would be to put the correct communicating stat with the furnace. That's how you maintain perfect temperature, which is the whole point of a modulating furnace.

    If you must use a binary on/off stat, Tranes work like this:
    When W1 calls, the unit goes to low fire, 40%, and stays there until the call satisfies. If it's really cold out, W1 cannot satisfy the call, then W2 second stage also calls. This starts a "ramp up" routine that increases output by 3% every minute(20 minutes until full output) If at any time W2 call drops out, it immediately goes back to 40%. The main blower fan matches speed to the burner output to maintain fairly consistent temp rise.

  3. #16
    Join Date
    Apr 2010
    Location
    Minnesota
    Posts
    515
    We've installed several Tranes on basic 2 stage stats. It works fine. I know nothing about the York logic, never seen it. But then again the key is to find a dealer that knows his stuff, because not just any installer can set these up correctly. And 5-10 years down the road when you need service on it, make sure you pick a dealer with a top notch service dept.

    If you think that w1-w2 logic is good, you should see a mod furnace with the actual communicating stat that's made for it. For instance the Tranes with the 900 control can adjust output 40-100% in 1% increments. The space temp is basically a constant flat line, no deviation from setpoint.

  4. #17
    Join Date
    Feb 2011
    Location
    North East Ohio
    Posts
    765
    As stated, YORK's modulating furnace works using runtimes and algorythms. The system can either use a communicating stat that will tell the furnace exactly what it needs, or it can use a simple single stage stat. When using the single stage stat, the unit works mainly on runtime. It starts at 35% and continues to ramp up very slowly(in 1% increments) until set point is achieved. I can take 12-15 minuts before you reach full output. I have had good results with systems using the single stage stats and using the 4 wire communicating system that YORK came out with. Either way you go, I am a big fan of the YP9C furnaces. As Dunkman said of the TRANE unit, the space temp is just about flat lined with these modulating systems. Furnace technology has come a long way in the last 20 years or so and I can't wait to see what comes next.

  5. #18
    Join Date
    Feb 2008
    Posts
    30
    Thanks for the feedback, guys. I am leaning towards the York for now to use with my existing wifi t-stat. Operating like NC described would work very well for me. And if I ever wanted to step up to the full blown communicating t-stat I could always do that later.

    Luckily my 16 year old system is still working fine (maybe I shouldn't say that too loudly?) so there is no hurry. not the most comfortable or efficient thing but it works well for what it is. And I know a lot more now than I did a couple days ago to help me work it out.

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