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  1. #27
    Join Date
    Oct 2008
    Location
    Raleigh, NC
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    21
    Quote Originally Posted by beenthere View Post
    With your rates. And using the temps you posted.
    Making a WAG, A duel fuel should save you better then 24%, providing your thermal balance point is 30F.(Thats 24% for that system, not total of both systems).

    Thermal balance point is the outdoor temp at which your heat pump can no longer heat the house by itself.
    And with those cheap gas rates. If you use set back. It won't cost you an arm and a leg to use the gas heat to recover.
    So the savings is a little better than what we originally thought. So it seems to me that if I knew I would be here for 20 years, the dual fuel would be the way to go. Otherwise, it really comes down to whether I want protection from potential rising utility costs. Would you agree?

  2. #28
    Join Date
    Oct 2008
    Location
    Raleigh, NC
    Posts
    21
    I just checked the gas rates since I was looking at past bills. Looks like they went up. The new winter rate (which starts november 1) will be 1.52/therm.

  3. #29
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    It is your choice.
    And I think your new gas rate should be taken into consideration, when you make that decision.

    Keep in mind. That the first floor unit always bears more of the heat load then the first floor.
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  4. #30
    Join Date
    Oct 2008
    Location
    Raleigh, NC
    Posts
    21
    I'll have to think about this a little bit.

    I was wondering about the setpoint. You mentioned 30. The two contractors who quoted me on the dual fuel mentioned that they set it at 40. Why is this?

  5. #31
    Join Date
    Oct 2008
    Location
    Raleigh, NC
    Posts
    21
    I will throw another wrinkle in here.

    I just found out that our electric provider has a rebate program for heat pumps (not dual fuel). It is $300. In addition, I would have to participate in a load management program for 5 years where they have 25% control over the ac and heat strips. This would also allow me to get a 10/month credit on our electric bill for 4-5 months during the winter, and a $4/month credit in the summer. Is this worth considering?

  6. #32
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Until you and the Ms. want to wrap Christmas presents in July and they shut down air conditoner at 3:00 in the afternoon.

  7. #33
    Join Date
    Oct 2008
    Location
    Raleigh, NC
    Posts
    21
    Quote Originally Posted by adrianf View Post
    Until you and the Ms. want to wrap Christmas presents in July and they shut down air conditoner at 3:00 in the afternoon.
    They told me that at 25% control the difference isn't very noticeable. Whether that is really true or not, who knows. I guess it is something to consider. I imagine it depends on what temp you like your house set at. Our tstat is no lower than 77 in the summer.

  8. #34
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Here in the Sunshine State when our provider F.P.L. turns off (demand side management) the air conditioning we get service calls. I'm not sure how they would control 25% of the a/c maybe someone else knows.

  9. #35
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    Quote Originally Posted by melbb View Post
    I'll have to think about this a little bit.

    I was wondering about the setpoint. You mentioned 30. The two contractors who quoted me on the dual fuel mentioned that they set it at 40. Why is this?
    They don't know how to plot a balance point.So instead of learning how to do it.
    They just set it to 40.

    Lot of contractors do that. It cost their customers more to heat that way. But they don't care.
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  10. #36
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    You should see weather dual fuel or electric aux saves you more in operating cost. And then see if the rebate, and load control save you more, and are worth the inconvience, of having a hot/warm house in the summer, and a cold/cooler house in the winter.
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  11. #37
    Join Date
    Oct 2008
    Location
    Raleigh, NC
    Posts
    21
    Quote Originally Posted by beenthere View Post
    They don't know how to plot a balance point.So instead of learning how to do it.
    They just set it to 40.

    Lot of contractors do that. It cost their customers more to heat that way. But they don't care.

    So how does one determine a good balance point for their system/climate? Do you have an offhand recommendation? I know it can take some trial and error, but it would be nice to have a starting point.

    I think I will go with the dual fuel and hope that we live in this house for a while. Maybe the savings will be more than I think. But I will think about it a little more.

  12. #38
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    An accurate load calc is the easiest way for a contractor.

    If you want to figure it out yourself.
    Trail an error.

    The simple way. Set the lock out to 30°. If it can't heat your house at 35, you know to raise it. If it is still heating the house at 30, lower it 5°. Repeat process until you find the balance point.
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  13. #39
    Join Date
    Oct 2008
    Location
    Raleigh, NC
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    21
    Quote Originally Posted by beenthere View Post
    An accurate load calc is the easiest way for a contractor.

    If you want to figure it out yourself.
    Trail an error.

    The simple way. Set the lock out to 30. If it can't heat your house at 35, you know to raise it. If it is still heating the house at 30, lower it 5. Repeat process until you find the balance point.
    The heat load for the downstairs was calculated as 38000 btu. I don't know how "accurate" the calculation is.

    With the HW IAQ t-stat can you tell when the gas is running, or do you have to go outside to check?

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