What size heating strips

Discussion in 'HVAC Heating & Cooling' started by lacomo, Jun 13, 2014.

  1. lacomo

    lacomo New Member

    Messages:
    2
    Location:
    MO
    Hi all, I have a question for you experts. I am in Missouri and I am buying a small house (1056 sq ft) It has a propane furnace I'm going to take out and put in a 2 1/2 ton heat pump. Do you think 10k heating strips would be big enough or should I go with 20k strips? Would the cost to operate be about the same and the 20k strips would just stay on a shorter length of time? Thanks in advance...Bob
  2. Lone Star Charles

    Lone Star Charles New Member

    Messages:
    14
    Location:
    Texas
    The old rule of thumb that I have used to determine reasonableness for heating is 10 watts per square foot for heating. If your house is poorly insulated, located in a very cold climate, has a lot of leakage, etc., you might want to increase that number. Also, keep in mind that the resistance heating is only supplemental to the heat pump, not the primary source of heat (unless your heat pump goes completely out). In theory, the cost to operate will be about the same; however, the cost to install will be significantly more. I guess that I would be leaning toward installing the 10k strip.
  3. Dana

    Dana In the trades

    Messages:
    2,783
    Location:
    01609
    A 10kw heat strip delivers 34,120 BTU/hr which is already something like 2x the entire heat load of most 1056' homes in MO, so it would more than cover you even if the heat pump was fratzed.

    That would be 32 BTU/hr per square foot of conditioned space. A typical code-min new home that size would come in between 10-15 BTU/ft at an outside temp of 0F. (99% outside design temps in MO range between +2F and +15F, depending on location. It get's colder than that for 1% of the heating season hours, but doesn't dwell at those temps long enough to matter, from a heating-plant sizing point of view.) Even if it leaked a lot of air and had the legal-maximum window/floor area ratio it would be tough to have a heat load more than 10kw, or 34,120 BTU/hr.

    If yours is an older home with 2-wythe brick walls, and no wall insulation, with single pane windows (without storm windows), you might have a heat load as big as 34 KBTU/hr, but not more than the combined output of the heat pump + 10kw heat strips.

    If the ducts for the heat pump are in an unconditioned attic, above the insulation rather than in a basement that will add some to the heating system sizing. Air sealing of both the ducts and the ceiling where they penetrate the attic insulation is critical in that type of installation.
  4. lacomo

    lacomo New Member

    Messages:
    2
    Location:
    MO
    Thanks guys, I appreciate it.
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