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  1. #1
    I live in central Maryland. Does anyone know about how much of the total annual operating time of a heat pump unit does the "auxiliary" (electric) backup heat run. I think the backup switches on when the outside temp is 40 deg F.

    We don't get really cold here, but the temp do drop down in the 20s for a number of days/nights in Dec and Jan.

    I would venture to guess it is 5% on average.

    Thanks.

  2. #2
    Join Date
    Nov 2004
    Posts
    2,927
    depends on several factors...but it's safe to guess that 5% is too low.

    if there is a prize for the correct guess then I will say ....

    34%
    Sometimes there are compounding complexities of multiple variables that are not intuitively obvious

  3. #3
    no prize jake..sorry.

    I'm asking to figure out how long it will take recoup the cost of heat pump from my ancient oil furnace/AC setup. I think I figured out that going straight HP has a very slight advantage (if not a wash) over HP/oil backup (at 35 deg F changeover). Diesel is getting pretty damn expensive while electricity cost is rising nominally (5% over last yr). My HVAC buddy is talking me into the Carrier variable hi-eff HP.

  4. #4
    Join Date
    Nov 2004
    Posts
    2,927
    Originally posted by dpoquette
    no prize jake..sorry.

    I'm asking to figure out how long it will take recoup the cost of heat pump from my ancient oil furnace/AC setup. I think I figured out that going straight HP has a very slight advantage (if not a wash) over HP/oil backup (at 35 deg F changeover). Diesel is getting pretty damn expensive while electricity cost is rising nominally (5% over last yr). My HVAC buddy is talking me into the Carrier variable hi-eff HP.
    The greatest savings would be with all electric heatpump.
    I say that because you mentioned "35 degree change over"
    An electric heatpump does not "require" changeover.It will run down below zero degrees outdoor temps.During the occasional defrost cycle the electric heat will come on,or if the pump needs some help on extreme cold days.

    I think your buddy is giving good advice.I dont like to junk a good furnace if has any life left though.Just do your homework and find a good contractor to select the correct size unit you need,ect..If there is already an air condition system installed then maybe your ductwotk will be usable,if not then ductwork will have to be sized to fit the heatpumps airflow needs.This could be the most expensive part of your project.
    good luck.
    Sometimes there are compounding complexities of multiple variables that are not intuitively obvious

  5. #5
    Join Date
    Jun 2005
    Posts
    40
    Here in Boston heat pumps are starting to come back the way gas and oil is here gas 26%-35%, oil 30%38% I bet itll be cheaper in new construction (buildings insulated well) I know it takes gas, or oil to produce electric, but I think its going to be cheaper. Alot more people calling us up to ask about it. Theres already alot of h/p's around here from early to mid 80's, were replacing

  6. #6
    Join Date
    Apr 2004
    Posts
    7,680
    XE you bring up a good point.

    For years, people said HP's dont work up North. Yet it's funny how they seem to be gaining popularity. What the trend says is that yes they do work but lack of understanding and reluctance has been the real problem.

    In Md, I would also go with a HP. Fossil fuel back up or "dual fuel" is nice but if not set up correctly can not only cost more to install but more to operate.

  7. #7
    Join Date
    Nov 2000
    Location
    Eastern PA
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    68,923
    Maryland is about the breaking point for dual fuel, but that may be changing fast with the cost of energy changing.

    I am seeing a lot more demand for dual fuel systems in Eastern PA.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  8. #8
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579
    Originally posted by dpoquette
    I live in central Maryland. Does anyone know about how much of the total annual operating time of a heat pump unit does the "auxiliary" (electric) backup heat run. I think the backup switches on when the outside temp is 40 deg F.

    We don't get really cold here, but the temp do drop down in the 20s for a number of days/nights in Dec and Jan.

    I would venture to guess it is 5% on average.

    Thanks.

    It varies for every heat pump installation. There is no such thing as a fixed value for a given location as you seem to be seeking.

    It depends upon the particular heat pump and how well the home is insulated and weatherstripped, the windows used, the solar gain, which way the home is oriented, etc...

    This is in addition to the local weather.

    Their are two balance points that come into play here. The heat pump balance point and the economic balance point. Each must be calculated for each individual heat pump installation. It is a custom thing not a rule of thumb for your area.


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