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  1. #1
    Join Date
    Feb 2019
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    Hmm Lennox SLP98UHV link W951 cut or not?

    Hello! Im a homeowner from Quebec!
    First post, let me know if Im rambling.
    We just had a new Lennox propane furnace installed (after 27 years with the old one!) The tech from our local contractor is literally younger than our Lennox system. We get inexpensive power from our utility (Hydro Quebec) with their Bi-Energy program ($0.0437 per kWh down to -12degC or 10degF and $0.2555 per kWh when its colder). So we have a heat pump for a/c in the summer and winter heating (down to -12degC) The heat pump control box gets a signal (dry contacts) from the utility meter when it gets colder, letting the propane furnace take over. Tech guys coming back one of these days to rewire the HPC3 because he thinks most of the wiring is unnecessary or redundant as the new SLP98UHP has all the bells and whistles to control everything...supposedly. The problem is blower speeds and defrosting. I like to keep the blower running (at a lower speed) in between heat or cool cycles for better ventilation and air filtering. Before the tech guy comes back, he has temporarily connected things with the following results:
    - With heat pump heating, fan blows at A2000 (he says rule of thumb is 400cfm per ton of heat pump - 5ton x 400 = 2000)
    - If the t-stat fan switch is set to ON, the fan blows at A2000
    - If its set to AUTO, it stops completely between cycles
    - During a defrost, the blower is at full speed. It gets cold in the house but the tech installed the sensor in the duct to cycle the propane on/off to keep the air from getting too cold, but this is not functional yet (he knows about it).
    - If t-stat calls for big increase, propane will start instead of HP
    - Propane starts at 35%, 7min delay to 70%, 10min delay to 100%, all with the blower speeds to match (A675, A1350, A1930)
    I guess all that is normal-ish, right? Can someone confirm that cfm/ton rule?
    The old furnace had a separate control/switch to keep the fan running at lower speed between cycles. I see the SLP98 has dip switches that could control this but does not the way its connected now.
    I have a Honeywell CT3611 thermostat. Is this a dual fuel stat or a 2-stage? Is it compatible with the rest of this system?
    An old Lennox HP19 single-stage 5-ton heat pump (for heat and a/c) with a timer for defrosts.
    And the SLP98UH110XV60C furnace. So, from what I read in the manual, is it possible the W951 link should be cut for my system?

    Id just like to be well informed before he comes back so I can ask the right questions and get the right results!
    Thanks for any advice!

  2. #2
    Join Date
    Jul 2010
    Location
    nebraska
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    If you use the communicating Lennox thermostat the jumper does not need to be cut . You'll also have greater control over blower speeds, dehumidification,much better heating staging and be able to set the switch over from HP to the SLP based on outside temperature. That's a very expensive furnace to be hobbled by a standard thermostat .

  3. #3
    Join Date
    Feb 2019
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    6
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    Thread Starter
    Thanks Martyinlincoln, my guy barely even noticed the stat. Ill definitely bring it up. Will a new, fancy thermostat handle an old-technology heat pump?

  4. #4
    Join Date
    Jul 2010
    Location
    nebraska
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    Yes it will.

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