Mini Split Assisted with Ducts
Last summer I installed a mini split in my 100yo house.
I am thrilled with what a difference 12k made for an approx 800sf first floor.
Yes I should have done a manual J, and that J would probably have led me to get an 18 k unit. Even so it was a transformational moment in our house and never did we have the levels of comfort on our fist floor.
I am aware of the existence pass through vents both with and without fans.
Is it possible to do a duct design to take the air that is conditioned in one room and move it around the house so that the other rooms can obtain more benefit.
In my case even with passive distribution (doors open) there is substantial benefit. My thought is that I could vent hot air from the ceiling back to the room with the mini split head and perhaps have a supply pass through on the bottom.
Will a manual D give me those answers? Should I just install ducts?
This is partially cost driven, but a good part of the magic of the mini split is not having to drive all of that air through a distribution system. This solution would essentially give more stale humid air to the to head unit thus making it work longer.
Thanks for you time
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The formula for heat delivered by moving air is CFM times temperature difference times 1.08.
Let's say you wanted to move a quarter of the cooling output to another room, or 3,000 BTU. And that room is ten degrees warmer than the room with the minisplit. You'd have to move 300 CFM in. You'd also have to move 300 CFM out. This isn't going to happen passively, it would require a big fan.
There's a reason that conventional systems put a duct in every room.
Thanks so much, I am at the stage of knowledge where I know how much I don't know.
I know you're taking an energy hit, but you do with ducts as well. My thought is that by connecting the rooms that hit can be somewhat minimized.
I can take my room dimensions and run some calcs.
You're absolutely right though 600cfm is a big fan. Seems though the other benefit is to remove the humidity. The delta t changes throughout the day. So in the case of my den there are probably four hours between June and September, potentially each day where this delta t is the real problem. I don't need the room to 68 deg at 40RH with stucco wall conducting a large part of the energy it is absorbing into the house.
Put another way the free lunch I am after is eliminating as much of the static load as possible.
Last benefit, if I did decide on ducts I would have explored all of the solutions from nothing to a fully ducted system.