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  1. #1
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    Sep 2007
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    Stupid dual fuel question

    When setting up dual fuel, I normally set the lock out at 35 degrees F. Should I disable the W/W1/W2 wire to not turn on the furnace during defrost?

    I have not done many dual fuel systems.

    Any help appreciated.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  2. #2
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    Single, Duel, or modulating furnace ?

  3. #3
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    Thread Starter
    Single
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  4. #4
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    I believe you can run the furnace during defrost to temper the air. With a low fire furnace option I see no problem. Seeing how your furnace is single stage I can't say it would be fine but I'm sure the residential pros will chime in and confirm. Which t-stat will you be using ?

  5. #5
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    Thread Starter
    Quote Originally Posted by VTP99 View Post
    I believe you can run the furnace during defrost to temper the air. With a low fire furnace option I see no problem. Seeing how your furnace is single stage I can't say it would be fine but I'm sure the residential pros will chime in and confirm. Which t-stat will you be using ?
    Thanks for the response.

    T-stat is Honeywell 6000 Focus Pro
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  6. #6
    Join Date
    May 2000
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    Indianapolis, IN, USA
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    Focus Pro? Do you have a dual fuel kit?

    We always hook up W or W1. Takes my friggin' furnace so long to fire that I get a blast of 40 air every defrost. I have a friggin' timed defrost which even at 90 minutes, goes in way too many times.

  7. #7
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    There are a few variables I take into consideration when making this call. One of them includes your backup heat source. If it is electric, I prefer to have one stage kick in with defrost. If it's gas or oil, it depends on how many stages your furnace is, 2 stage, I'll kick in low fire, if it's single stage I usually do not use backup for defrost unless the heat pump is running unrestricted or with a low lockout for whatever reason. This also relies on the defrost demand, if it's a timed defrost you have to weigh the value of firing so frequently. One thing I'm picky about is always using a worthy thermostat with dual fuel setups. Always use an outdoor temp sensor.

  8. #8
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    Thread Starter
    Quote Originally Posted by taylor2 View Post
    There are a few variables I take into consideration when making this call. One of them includes your backup heat source. If it is electric, I prefer to have one stage kick in with defrost. If it's gas or oil, it depends on how many stages your furnace is, 2 stage, I'll kick in low fire, if it's single stage I usually do not use backup for defrost unless the heat pump is running unrestricted or with a low lockout for whatever reason. This also relies on the defrost demand, if it's a timed defrost you have to weigh the value of firing so frequently. One thing I'm picky about is always using a worthy thermostat with dual fuel setups. Always use an outdoor temp sensor.
    Thanks. Good info.

    I always use and outdoor sensor as well.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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