Minisplit design/Manual J question
I am working with an HVAC contractor to design and install a multisplit system for our 1950s ranch renovation. As an FYI, we’ve done a substantial amount of upgrades to improve the tightness and insulation of the home although at 60 years old the house still isn’t perfect. I’m now hoping to replace our aging ducted air handler with a new ductless system. Motivation to go ductless is driven by many factors that I won’t get into in this post (both efficiency and a more practical issue of headroom in our finished basement).
Our contractor has run a detailed Manual J and has provided me the report using a program written by Wrightsoft. I’m happy to attach the report if this would help. The open question is how to handle three guest bedrooms that are all connected via a single hallway. The rooms are occupied (our three kids) so I do want a solution that prioritizes comfort (i.e. I don’t want to place a single unit in the hallway and hope the rooms are comfortable when the doors are shut).
The contractor has presented me with two options (all Mitsubishi):
1) installation of small 6K wall units in each room (MSZ-GE06NA-8)
2) installation of a single 12K ducted unit for all bedrooms (SEZ-KD12NA4R1.TH)
Below are the calculated loads for heating and cooling in each room and in total:
ROOM NAME; Area (sqft); Htg load (Btuh); Clg load (Btuh)
Bedroom 1; 225; 3372; 2392
Bedroom 2; 192; 3127; 2127
Bedroom 3; 156; 1586; 1551
Bedrooms Total; 573; 8085; 6070
I’m hoping for advice/thoughts on which approach is recommended when balancing performance, efficiency and comfort. It seems like either way I will loose efficiency – either oversizing the units or using ductwork.
As a final question, given I’m in Chicago I also wonder whether there would be any merit in going with a hyperheat model in each BR. While I like the ability to heat to a lower temperature I think these units would create an even larger oversizing issue (I believe these start at 9K BTU).
Lastly, I do plan on adding supplemental heat in any scenario. I’ve recently installed high-efficiency fireplace inserts and I plan to also add some electric radiant to have a set and forget option. To be clear though, I really want to find a multisplit design that heats our home (comfortably and efficiently) for 90%+ of the winter. If that’s not realistic then I’ll grudgingly keep a forced air system.
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