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HVAC suggestions

Sandesh Tawari
4 months ago
last modified: 4 months ago

We are soon to apply for building permit for our 2-story house in Bay Area, California, and need to figure out HVAC plans. I am really new to this and could really use help from experts and experienced folks on this forum. There is about ~2200 sq ft on first floor and 1500 sq. ft on the second floor. Foyer is double heighted. There is an ADU as well, but I am less worried about it due to its relatively simpler needs.

HVAC design engineers that our architect hired has proposed running ducts through crawl space, with registers on floor and return air register in ceiling (above refrigerator and some cabinets). For second floor, the proposal is to run ducts through attic, with registers in ceiling as well. As much as I understand this, it seems it is a horizontal ducted set up, where a single heatpump outside will be connected to two air handlers, one upstairs and one downstairs. The air handlers then would branch out to individual registers. This way, we have two zones. Please see attached images. One of the things I am trying to figure out is whether I should have two separate heatpumps - one for upstairs and one for downstairs. Based on the little I researched, folks seem to suggest that multi-split set up isn't ideal for efficiency sake. But I don't know whether this matters so much in Bay Area weather.

I would really appreciate any feedback on this, what should I watch out for, what questions to raise with my architect and such. Given that we have some room here to iterate, I can work with architect/hvac engineers to modify things.

Tenantive model for heatpump: HVAHP060B21S, Airhandlers: HMAHP48D21S (first floor), HIDH036B22S (second floor).

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