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Heating capacity of ductless system: 23K Btuh vs. 25K Btuh

T_L | Posted in Energy Efficiency and Durability on

I am looking at having installed a Gree ductless system into my older, 2-story, not tightly sealed home in Puget Sound area of Washington. The house was built in the 1950s at the latest, may be older by the style.

My question is whether it is worth the extra $600 for a 2K increase in BTUH? I am aiming to heat the lower level of the house, with high ceilings. The unit would go into a large open area at the front of the house, hoping some of the heat will find its way to the back of the house.

I have used wood heat in past years, with a ceiling fan in the open front area and a box fan in the hallway to move heat to the back. Not against continuing the fan setup.

So, $600 for an extra 2000 BTUH, and seer /eer increase from 18/12 to 21/13, EVO+ vs the Terra. Worth it?

Thanks for the input.

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  1. mackstann | | #1

    You really should have a heating load calculation done, and then you'll know exactly whether that extra 2000 BTU/h is necessary or pointless. Without a load calculation, even an HVAC genius will just be guessing.

    However, the increase in efficiency is substantial, and it may well be worth it for that alone. That would also require a load calculation to be done, to figure out how much energy it will be using and how long the extra $600 would take to pay itself back in lowered electric bills (keeping in mind the uncertainty of energy price inflation, possible future carbon tax, etc.).

    For heating, the efficiency metric you want to focus on is HSPF. EER/SEER are measurements of cooling performance.

    I suspect that the ceiling fan will not be as useful with the mini split, but the hallway fan might be, depending on your home's layout and door closing habits.

  2. T_L | | #2

    I know that for Seer/Eer, the higher the number the better. Is that true on Hspf as well? You are right that my concern is heating, not cooling. You are the first to tell me that is Hspf, not the Seer number everyone seems to focus on. The Evo+ is 10 vs 9.5 for the Terra. Again, I have no idea how big a deal that .5 difference makes.
    Best guesses is likely all I will get for load calculations. Front of house has lots of windows on each exterior wall, with glass doors between front rooms and middle rooms. Back of house has one each room.
    Thanks for your help.

  3. GBA Editor
    Martin Holladay | | #3

    For EER, SEER, and HSPF, the higher the number, the better.

    For more information on these three rating units, see SEER, COP and HSPF.

  4. T_L | | #4

    Thanks everyone.

  5. Expert Member
    Dana Dorsett | | #5

    If the home is air-leaky, has only single pane glass or really thin attic insulation you can probably peel off 2000BTU/hr of peak load with air sealing and spot-insulation, or maybe 3-4 low-E storm windows for that $600, and be more comfortable to boot.

    Careful heat load calculations should give some clues as to where the $600 might buy you more than 2000BTU/hr of load reduction.

    Most leaky 2-story 1950-ish homes will have a heat load more than 23K @ 20-25F outside design temps though, but with some tightening, spot insulation, and low-E storm windows (or <U0.35 replacement windows) it could hit that range. Air sealing is usually the first-best bang/buck (especially basements, band-joists, and top-floor ceilings, and any flue/plumbing chases that run from basement to attic & beyond) followed by insulating any parts that have none (foundations are almost never insulated on homes that vintage) or are easy to add to (attics).

    Replacement windows are WAY down the list, but wood sash single panes that can be tightened with weatherstripping and tight LOW-E storm windows can outperform code-min replacement windows, at a much lower installed cost. The box stores carry Larson low-E storms, but it's worth upgrading to the Silver or Gold series over their low-end Bronze that are most likely in stock, for the better air tightness and nicer hardware. Harvey has the tightest storm windows in the biz and have a hard coat low-E option, but aren't sold through retailers to the DIY set.

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