Can a/c ducts heat house

Discussion in 'Quotes and Proposals' started by ron wiley, Aug 3, 2011.

  1. ron wiley

    ron wiley New Member

    I have several quotes from contactors who all claim the heating proposed will work in my house. I'm skeptical.
    Here's what I have. A 2 story contemporary with a one story family room at one end of the house. Aprox 2300 sq ft.
    The A/C unit is in the attic along with the ducting. Heating is baseboard resistance electric.
    I believe the cooling capabilities will be fine.
    My concern is that blowing the heat into the A/C ducts in the attic will not provide a comfortable even heat in all rooms. All the duct vents are in the ceilings with a large central return vent at the top of the stairs in the second floor ceiling.
    I like to be warm and set the stat at 72*, or higher. I don't want settings of 68* and a sweatshirt or jacket needed.
    We see winter temps here in Pa down to single digits and below 0* on occasion.
    Will a central air ducting work for a heating system.
    Maybe some of you contractors have some experience with this.
    Comments please. Thanks
  2. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader


    You need help.

    You need to either learn more or find a good contractor. When I take on a retro-fit, I need to be at one with the owner as to what he wants and what I can do to get him there.

    You are well on your way as you state what your comfort levels are, but you dis-allow for advanced delivery systems, calm down and restate your goals. You want this to be a geothermal system?

  3. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    There are plus and minuses to all delivery systems.
    I heat my home in MI top down. Lake proximity has us on a crawl which had to be rebuilt which required relocation of ducts to attic. Convienience was the plus side of this delivery, but even with a low central return, I'm not sure it is as comfortable along the floor as before.
    Might be my imagination, I haven't measured. I'm looking forward to new unit with variable speed motor see if it mixes it up more.
  4. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I think it preferable to place the ductwork to favor dominant mode. In other words we cool 8 months per year in FL so high wall / ceiling ductwork is favored.

    In cold climates it would seem preferable to have floor supplies. Will it work the other way? Of course.

    The bigger issue is likely duct sizing / airflow. Ducts that are adequate fo a PA cooling load may not cut it for geothermal heating...airflows of 2-3x may be required. A complete Man J and Man D calculation is needed to know for sure.
  5. ron wiley

    ron wiley New Member

    Thanks, Curt.
    Two to three times of air flow for heat vs cooling has not been mentioned to me before. That seems like a tremendous difference.
    What is a 'Man J' and 'Man D' calculation?
  6. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    ACCA Manual J whole house heating and cooling load calculation.

    Man D handles duct sizing.

    Ducts sized for cooling use air cooled by 20*F to cool a house to, say, 75* when it is 90-95 outside. For a typical bedroom that might mean 100 CFM of air is needed

    In heating mode a geo system uses air heated by 25-30* to heat a house to, say 72* when it is 0 outside. The same typical bedroom might need 200 CFM of air for heat.

    Ducts designed to meet a cooling load up north likely won't be able to flow the required air if geo is used for heating.

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