I would like some opinions from all you smart people.

I have read many of the articles/posts on this site about a one head per floor minisplit approach for a net zero buildings. I do gut renovations of row homes in DC and have LEED Platinum certification on some, but have not achieved net zero. But I really want to!

Since these are existing ~100 year young brick rowhomes, mostly with attached frame porches, we cannot achieve a passive house tightness with our current construction techniques. We achieve in the neighborhood of 3.5 ACH50.

I have a project starting next week that is a classic example. It's 20' wide x 30' deep with an 8' porch addition that we will enclose. 2 floors (750 per floor) + basement.

I've attached two schematic designs: A) Exhaust only and B) ERV I realize there are many flavors of options in between and I'm open to all comments.

Specific questions:

1) Given our likely 3.5 ACH50 is getting heating and cooling along the entire length with one head feasible? and or reasonable?

My sense is that if it were <1 ACH50, a candle would heat the place...but I've got triple the infiltration...so I have concerns about comfort. In particular at the rear, where there are 3 exposed sides, as opposed to the main house where there are party walls.

2) There is a due west exposure on the rear (DINING AND MASTER BR).

DC Summers are HOT and humid. However, we are a heating dominated climate, when you look at the numbers.

3) Given our likely 3ish ACH50, is exhaust only a reasonable approach? Would you do it in your own home?

It seems to me that with that amount of leakage, which is only somewhat tight, my money would be better spent on an exhaust only system (forgoing the whole house ERV and associated ducting) and put that in higher efficiency mechanicals.

I am working with an experienced installer/designer and the energy model and J are forthcoming which will help answer some of these questions. However, i'd appreciate folks chiming in from a real world installation perspective on actual comfort.

Best regards, Tanya