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  1. #1
    Join Date
    Oct 2005
    Location
    Kansas
    Posts
    2
    If you use a Honeywell 8320 with a heatpump with backup fossil fuel do you need to use the Lennox FM21 or can it be eliminated?

  2. #2
    FM21 (fossil fuel kit)?

    If so, you can use a Honeywell outdoor temp sensor with the VP and use the Honeywell VP to control the system.

  3. #3
    Join Date
    Oct 2005
    Location
    Kansas
    Posts
    2
    The FM21 is a fossil fuel kit. This is a Lennox system with an XP19 two stage heatpump with G61MPV two stage gas furnace with variable speed blower. It seems like there is a conflict between the thermostat and the fossil fuel kit.

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,898
    The VP will handle the 2 stage heat pump but only 1 stage of backup. You'll have to use the boards timer to stage the gas heat. Not sure how the Fuelmaster does it. If you can get a dual fuel control that handles 4 stages, would be better. Or a stat like the W-R 1F95-391 that does.

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