I’m in the middle of an extensive renovation of a 150 year old house in zone 4a with design-day temp of 17 (Long Island, NY). It is tall and narrow, with the kitchen and dining room in the double-wyth brick basement. The basement is mostly below-grade on the south side, sloped on the east, and above grade on the north and west sides. The north/south are about 15′ wide, and the east/west 30′ long, plus a 7′ framed addition on the north side (with a subbasement below it). The basement has been completely gutted, and a new slab poured over 2″ (low-gwp) XPS, with slab-edge insulation. The 2×4 walls are stood 1″ away from the brick, and will be insulated with CCSF. The windows are being replaced with Marvin Ultimate dual-pane casements. Not the most energy-efficient, I know, but there were other considerations.

My issue regards HVAC. We currently have (grossly oversized) multi-splits – the house had 3 heads on a 32k and and 4 on a 48k Carrier outdoor unit. We’ve removed the 80kbtu atmospheric boiler that was supplying a poorly-designed hydronic system, and intend to solely rely on the mini-splits. We’re installing a Zehnder ERV. I’m particularly concerned about oversizing (and resulting summer humidity problems) and the poor-modulation of multi-spits, and am wondering if precise locations of the ERV supply/return ducting would allow a single head on a 1:1 system to maintain even temps throughout the whole space. I imagine this approach would function best with the head located in the top (north) area, as it has far more window/wall ration than the dining room, but that is also where a conventional ERV design would specify the exhaust be.

Thanks!