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  1. #14
    Join Date
    Jan 2005
    Posts
    86
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    I have a Lennox G60DFV downflow 2 stage furnace with a White-Rogers control board.

    Stage 1 (Low heat stage) of furnace is 68% of stage 2 high heat. Going to stage 2 right from the start will let you get to the desired temp some 5 (corrected) minutes earlier (depending on ambient outside temp.).

    You said that the furnace runs in stage 1 for 15 minutes before switching to high heat. On my furnace control board, DIP switch #3 allows you to select high heat after a 10 or 15 minute minute run in low heat (10 minute delay with switch ON). Changing the delay for high heat to 10 minutes will help you.

    To conclude: setting high heat delay from 15 minutes to 10 minutes and starting temperature recovery some 5 to 10 minutes earlier will give you the same results as a 2 stage thermostat (2 stage thermostat also needs at least one additional wire).

    P.S. On my furnace, you have to change the setting of jumper E20 before going to a 2-stage thermostat.

    I mentioned a saving of 5 minutes in high heat only.

    Here is a more accurate calculation:
    Assume a 80,000 BTU/hr high output and a 70% low heat output of 0.7 x 80,000 = 56,000 BTU/hr.

    Assume furnace takes 1 hour to reach desired temp with 15 minutes on low heat.
    15 min. on low heat = 56,000 x 15/60 = 14,000 BTU
    45 minutes on high heat = 80,000 x 45/60 = 60,000 BTU
    Total output in 1 hour = 14,000 + 60,000 = 74,000 BTU.

    Time to produce 74,000 BTU in high heat only =
    = (74,000/80,000)x60 = 55.5 minutes.

    Conclusion: going to high heat from the start saves 4.5 minutes to raise temperature by 2*C

    [Edited by deme on 03-11-2006 at 11:55 AM]

  2. #15
    Join Date
    Mar 2006
    Location
    Great white north
    Posts
    57
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    I would only use this new thermostat for heating. I have no A/C (not really needed for household where I'm at) and no humidification (Don't need the hassle and added work).
    Thanks

  3. #16
    Join Date
    Mar 2006
    Location
    Great white north
    Posts
    57
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    to deme,
    mine is exactly the same (dip switch #3 controlling board timer (15 vs 10 min) and E20 jumper for thermostat).
    I have mine set up the way the way it is (15 min 2nd stg delay), mainly for when it is maintaining heat when it is really cold, as 1st stage typically can satisfy the thermostat demand within 15 min.
    I tend to overanalyze things, and this is probably another situation. I guess I'll take from what I learned here and look into it some more. Atleast now, I'm better informed.
    Thanks
    javaman

  4. #17
    Join Date
    Jan 2005
    Posts
    86
    Post Likes
    Originally posted by javaman
    to deme,
    mine is exactly the same (dip switch #3 controlling board timer (15 vs 10 min) and E20 jumper for thermostat).
    I have mine set up the way the way it is (15 min 2nd stg delay), mainly for when it is maintaining heat when it is really cold, as 1st stage typically can satisfy the thermostat demand within 15 min.
    I tend to overanalyze things, and this is probably another situation. I guess I'll take from what I learned here and look into it some more. Atleast now, I'm better informed.
    Thanks
    javaman
    I made a more accurate assessment of the time saved in high heat only. You save only 4.5 minutes!
    See my twice-edited original post.
    I too tend to over analyze! It's fun!

    Regards Deme

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