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Mini Split Equipment Selection Zone 3A

maks8489 | Posted in Mechanicals on

I’ve been going in circles trying to choose a mini split system to replace my 36(!) year old heat pump. Would love a little sanity check or guidance from some of the brilliant minds here regarding sizing. Also interested in opinions on whether  I should even be looking at Hyper Heat units & particular model recommendations in regards to their modulation ranges.

The house will be about 1,475 sq ft after a planned 270 sq ft addition. Single story, built 1984, vented attic with very little insulation, vented crawl space, north Alabama climate zone 3A. I’m going from a packaged 2 ton heat pump that’s falling apart with terribly leaky ducts in crawl space to a Mitsubishi mini split with air handler(probably SVZ) in hall closet, new ducts in attic consisting of two straight, similar length trunks & several straight branches. I will be doing considerable air sealing & insulation in the attic.

I did a Manual J, including the room addition & got a heating load of 31,627 BTUH, sensible cooling load of 24,456, latent load of 3,435. This would seem to suggest something like the SUZ-KA24 or even SUZ-KA30. But am I right in thinking that’s a little over-sized given my current configuration? Granted, the current unit struggles to keep up at times, but I would assume that has more to do with it’s age & condition than anything else.

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  1. user-2310254 | | #1

    Not having the ducts in the vented attic would be better. That said, 2.6 tons doesn’t sound oversized (but that’s a WAG). Zone 3A is pretty mild heating-wise, so I don’t know why you would need a hyper heat modal.

    Can you provide more detail about your structure? Can you upload your Manual J?

    1. maks8489 | | #2

      Yes, I know ducts inside the envelope would be better, but this is what I have to work with. I couldn't see much use in the Hyper Heat either, honestly it was a comment by Allison Bailes over at Energy Vanguard that made me wonder if I was missing something there. I'll attach my Manual J.

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