I have a Carrier gas furnace and AC forced air system. Am looking to replace the system in the near future. My home is a (uninsulated exterior wall) brick 1200 sq ft cape cod style, consisting of 2 downstairs beds, bathroom, living room which is not very open to the kitchen (only 36" doorway), and converted sunroom to dining room. The dining room does not have insulation in the floor which makes it colder in the winter. The upstairs is a converted half story attic that is the master bedroom, with knee walls and attic space. Also a full basement where the ducting and furnace is. I live in NW Ohio where we see temps as low as -5 up to 100 F.
I struggle to keep the upstairs cool in the summer as I have only one vent in the room, and the staircase has no air conditioning which is also affected by the heat and cold from the exterior and attic knee walls. Which brought me to be interested in a mini split HVAC unit for the upstairs. Upon research I have found where the mini split systems can have multi heads run off of one outdoor heat pump. I've spent the past few days configuring different options for Mitsu and Daikin, and even Fujitsu, however, have started to shy away from Fuj due to the comments I've seen posted here.
I was planning on a wall head in all 3 bedrooms, and one each in the living room and kitchen. However, I was trying to minimize cable runs, expense, and the bulk of the units in each room. So then I started looking into one wall head unit upstairs and a ducted head unit either in the open attic space or the basement. I'm not sure if it matters or which would be better, to have the supply vents come from the ceiling or if the current floor registers would ok still. Also factor in the extreme heat and cold in the attic space where the ducts and unit will be vs the somewhat cool basement. Then I also question if the one ducted head unit would be able to cool and heat the whole downstairs efficiently. Question: Can the wall units have the cabling ran through the interior wall or will they not be able to make the bend, I ask as I see a lot of units installed on an exterior wall and ran outside with speedy duct, which I DO NOT want to do.
I also started looking into furnace replacement air handlers that can be adapted to my current ducting, for instance the Mitsu MVZ. I'm a little confused on what would be required though. I though it would act as another head on a multi outdoor compressor, however, the videos I am watching make it look like I will need one of the dual fan outdoor compressors connected to a branch box. I also am unsure of how many BTU I need for the home in general (my calc was a 24,000 system) and also having the system oversized, decreasing efficiency.
At this point I'm kind of torn, whether to continue looking into the mini split systems, or if I should just replace the furnace with a heat pump air handler and outdoor heat pump from a brand like Carrier and just continue using my current ducting. I still question if I still still have the cooling issue upstairs in the summer without a mini split head unit, which is why I looked into the Mitsu MVZ as it would integrate into the heat pump that would connect with the upstairs head unit.
My last issue is the heat pump being able to keep up on the very cold 0 degree days we see from time to time. I've read that over the past few years they've made advancements where the better brand heat pumps have a defrost cycle/heater that runs and melts the possible ice that forms which causes the heat pump to not be able to produce enough heat on those days.
I know this is long, but any feed back would be greatly appreciated. I do have a family friend who works HVAC which I still need to call and have come out to assess my situation.
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