Dual Fuel HP -- A Semi-Technical Question
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  1. #1
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    Oct 2005
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    N Metro Atlanta GA
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    When the HP calls for fossil fuel furnace backup, the HP stops heating (unlike electric backup).
    Does the HP start heating again during this cycle OR does the furnace alone take the system up to the set point?

  2. #2
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    Nov 2000
    Location
    Upstate, SC
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    2,919
    It depends on the system or add-on heat pump kit you have. It can be done either way. Some fire the furnace all the way until 1st stage is satisfied and some can bring the HP back on when 2nd stage bulb is satisfied and the furnace cuts off. I prefer to fire the furnace on to satisfy the stat once it calls for 2nd stage and the furnace fires, but I have seen it done both ways. The important thing is that the furnace and heat pump don't run at the same time.

    Bobby

    [Edited by BobbyBJr on 10-25-2005 at 09:21 PM]

  3. #3
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    Oct 2005
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    The furnace will satisfy the temp in the house because the heat from the furnace going across the coil will be very high. If the heatpump runs with the furnace the furnace will cause the pressures in the heatpump to skyrocket thus causing damage. In a normal heat pump application the coil is before the electric heat and in a duel fuel application the coil is after the furnace heat. Hope that makes since to you

  4. #4
    Join Date
    Oct 2005
    Location
    N Metro Atlanta GA
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    Originally posted by wayner211
    The furnace will satisfy the temp in the house because the heat from the furnace going across the coil will be very high. If the heatpump runs with the furnace the furnace will cause the pressures in the heatpump to skyrocket thus causing damage. In a normal heat pump application the coil is before the electric heat and in a duel fuel application the coil is after the furnace heat. Hope that makes since to you
    I think I understand what you are saying (at a civilian's level of course ). To test my grasp of the situation, it sounds like I have 2 heat source scenarios:
    1. The heat pump handles all heating when the outside temperature is above the balance point.
    2. On colder days/nights, and when the HP calls for backup, the furnace handles all heating and the heat pump does not run.
    Am I close?

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    33,811
    3 ways this is done.

    1. Heat pump is 1st stage, gas is 2nd stage. If 2nd stage calls, pump shuts off gas takes over til 2nd stage satisfies, 1st stage keeps heat pump on.

    2. Same staging but dual fuel kit locks gas on until both stages are satisfied.

    3. No staging. If outdoor stat says warm enough for pump, that's all you get. If too cold, all you get is gas. This is how the Vision Pro dual fuel setup works.

  6. #6
    Join Date
    Oct 2005
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    68
    You got it!!!!!

  7. #7
    Join Date
    Oct 2005
    Location
    N Metro Atlanta GA
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    70
    Thanks! You guys are really helping a lot of people around the country.
    Originally posted by BaldLoonie
    This is how the Vision Pro dual fuel setup works.
    Is a model of the Trane XL800 thermostat the same as the Vision Pro? If so, I think I can get the thermostat warranty extended to 10 years also.

  8. #8
    Join Date
    Oct 2005
    Posts
    21
    Originally posted by BaldLoonie
    3 ways this is done.

    1. Heat pump is 1st stage, gas is 2nd stage. If 2nd stage calls, pump shuts off gas takes over til 2nd stage satisfies, 1st stage keeps heat pump on.

    2. Same staging but dual fuel kit locks gas on until both stages are satisfied.

    3. No staging. If outdoor stat says warm enough for pump, that's all you get. If too cold, all you get is gas. This is how the Vision Pro dual fuel setup works.
    How does a carrier infinity 13 duel fuel with the thermidistat work it's staging? I have some quotes w/outside tstat & some without.

  9. #9
    Join Date
    Oct 2005
    Posts
    68
    If your getting a carrier infinity system get the infinity stat too.

  10. #10
    Join Date
    Oct 2005
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    21
    I got a quote on a carrier Performance 12.7 & Infinity 13 SEER. There is quite a few dollars difference in price. Is the 13 that much better?

  11. #11
    Join Date
    Mar 2004
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    1,042
    Originally posted by ????
    Originally posted by BaldLoonie
    3 ways this is done.

    1. Heat pump is 1st stage, gas is 2nd stage. If 2nd stage calls, pump shuts off gas takes over til 2nd stage satisfies, 1st stage keeps heat pump on.

    2. Same staging but dual fuel kit locks gas on until both stages are satisfied.

    3. No staging. If outdoor stat says warm enough for pump, that's all you get. If too cold, all you get is gas. This is how the Vision Pro dual fuel setup works.
    How does a carrier infinity 13 duel fuel with the thermidistat work it's staging? I have some quotes w/outside tstat & some without.
    Mr./Ms. ????,

    You need to specify that you're talking about the Infinity 13 dual fuel *package unit*- not a split system (this came up in another thread). The Infinity package units are not yet compatible with the Infinity control, so the Thermidistat is the fanciest control available for those.

  12. #12
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    Oct 2005
    Posts
    21
    Package unit replacement.

  13. #13
    Join Date
    Mar 2004
    Posts
    1,042
    Using an outdoor thermostat to control fuel selection is a pretty rudimentary control system.

    You'll get better function and comfort from using the Thermidistat to control dual fuel operation (it will need the outdoor temperature *sensor* to do so so that the Thermidistat knows outdoor temp). The difference is mostly in how it handles defrosts and recovering from setback periods.

    Depending on how you configure it, it will work in style number 2 or 3 as shown in this thread. You can define max outdoor temp for using gas, and min outdoor temp for using heat pump. If the two temps aren't the same, the thermidistat can choose the fuel source on its own based on the amount of demand for heat. Either way if it fires up the gas burner for any reason, including a defrost, it will continue burning gas until there is no more call for heating or defrosting.


    [Edited by wyounger on 10-28-2005 at 06:38 PM]

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