Mini-splits in a multi room house
I’m in the design phase of a four-bedroom house. I just got preliminary drawings for the mechanicals from a ME. I had asked him to draw it up for mini-splits, which is a new technology for me but everyone raves about how great they are.
The first floor is an open plan with kitchen, dining room area, living room area and family room. The second floor is three bedrooms. Third floor is about a 200 SF office. Basement has the fourth bedroom, plus a workshop and mechanical room.
His proposal is to put a head in every room — four on the first floor, three on the second floor, one on the third floor and two in the basement. Ten heads total. The head specced is a Daikin FFQ09Q2VJU, which is a ceiling cassette rated at 9K BTU/hr. He calls for four compressors outside.
I haven’t seen his Manual J, but I used an online calculator and got in the 30-40K range for both heating and cooling. I’m in zone 3.
So my first question is, am I right in thinking that this system is way oversized, with 90K BTU when it needs about a third of that?
Second question is, OK, how should you configure a minisplit system when you’ve got lots of rooms? With the open plan on the first floor I could see having one or possibly two heads. But what about the bedrooms? What do you do when there’s a good possibility the rooms will have their doors closed a lot of the time?
He also calls for an ERV ventilation system with ducts in every room. Can that be counted on to distribute heating and cooling and possibly reduce the number of heads?