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  1. #1
    Join Date
    Oct 2006
    Posts
    15
    This is probably going to be a tough question to answer, but I'll put it out here anyway...

    We just had a Trane XL19 air conditioning system installed over the summer. Our house also has a new oil burner with hot water radiator heat. We live in the New York City area.

    What I'm wondering is, for milder outdoor temperatures (say, above 45 degrees), would we be better off using the heat pump feature of the XL19 rather than the radiators (keep in mind that the oil burner provides us with hot water as well)? I believe we're currently paying about $.21 per kwh after fuel price adjustments, and oil is about $2.50 per gallon, but I would think that oil prices and electricity prices should stay more or less in proportion to one another (our electricity is generated with natural gas). One other factor is that the HVAC registers are mounted on the ceiling, which isn't ideal for heating.

    Thanks.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,599
    ASS-U-MEing 80% AFUE boiler, there would be some savings running the heat pump down to 35-40 out over heating with the boiler. Even though the boiler stays hot for domestic water, the burner would be required for home heating. I cruch a few pennies more for the burner over the heat pump. Also, if you just need to take the nip out of the air, the heat pump can do it in short order. Takes a while to get the radiation hot enough to heat the air, especially if old radiators not copper fin-tube baseboard.

    If it were me, I'd do the heat pump down to 40ish then turn the boiler on after that, especially if the forecast is for continued cold.

  3. #3
    Join Date
    Oct 2006
    Posts
    15
    Thanks for the response. In case it wasn't clear, the entire boiler (not just the burner) is new; it's a Peerless boiler with Riello burner that were both installed last year, however, as far as I know it's not a super high efficiency model. And it's all one unit, with a hot water coil, so the boiler DOES need to run somewhat whenever the hot water temperature drops.

    Is there a point at which the heat pump really starts losing efficiency? Is the curve of heat efficiency vs. temperature linear or exponential?

    [Edited by smwsmw on 10-10-2006 at 02:51 PM]

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,599
    The curve is fairly straight. To know when the pump alone can't do it, you'd have to plot its output against the heat loss of the house. Your boiler setup is probably 85-86% AFUE which would put it about on par with the heat pump.

  5. #5
    Join Date
    Oct 2006
    Posts
    15
    Thanks...in that case, I guess it makes sense not to use the heat pump at all, since it would just be additional wear and tear on a very expensive system. Boilers are cheap by comparison (and generally last longer)....

  6. #6
    Join Date
    Feb 2003
    Posts
    1,996
    At least you have the option to choose now. Oil prices have dropped, but Con Ed and KeySpan have already stated that electric/gas rates will not drop since they already purchased gas contracts this past Spring and Summer when the nat gas prices were still high.

    Last year, I used my heat pump mini-splits in the early part of the winter. But since then, LIPA electric rates have increased by 50%. Now I just, throw the HP on for 20 minutes in the early morning for a quick warm-up.

    Am I saving aything, probably not.

    Curious as to why you spent extra for a heat pump in the NYC area when we've always had the highest electric rates in the country.

  7. #7
    Join Date
    Oct 2006
    Posts
    15
    Actually, I'm a LIPA customer as well...I just said NYC area because everyone knows where it is...

    Anyway, I didn't pay extra for the heat pump, it's included in the XL19i.

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