I’ve read a ton of stuff on this site and learn something all the time, so thanks in advance to all. This is my first post, so please be gentle. 🙂
I live in the Boston, MA area. I am finishing my basement. I want to have the option of both heating/cooling, but I have headroom concerns, so I naturally gravitated to the idea of mini-splits for the basement to avoid any more duct work. In addition, the duct work for my first floor takes up a lot of headroom in the basement. When I pointed that out to several contractors, they suggested incorporating the first floor HVAC into the mini-split system and split the first floor into two separate ducted air handlers, each with a backup hydro coil for heat coming from my existing oil boiler. This will eliminate 90% of the overhead ductwork causing issues with headroom. I have really only discussed this with Mitsubishi dealers. The equipment suggested has been:
– MXZ8C48NAHZ2 as the out door unit
– A SVZKP24NA and a SVZKP12NA to cover the two sides of the first floor
– Two MSZFH09NA’s and one MSZFH06NA for the basement’s three rooms
I got wildly varying quotes in terms of cost months ago. Some contractors only had three 6,000 BTU systems in the basement. All agreed I needed three heads in the basement.
Now that I am close to doing the install, a couple of the contractors have said that their Mitsubishi rep has advised against this plan, even though it is done according to the spec. I’m getting very little detail as to why. One dealer said he was concerned with the small rooms in the basement getting over-heated or over-cooled with the first floor units are calling, even if the basement units are off. I saw that mentioned in an article here as well. The reason for the three units in the basement is that two of the rooms will often have their doors closed, with double-wall and under-door soundproofing, so there won’t be a lot of air flow into them and, in addition, there could be a lot of people in the media room so it was recommended to make that one larger than its size may dictate. See attached to try to help explain.
So, I am at a bit of a loss of what to do. I like the idea of getting back my headroom, being more efficient and having more control over the two sides of the first floor. But, I don’t want to do this if it won’t work correctly or won’t be efficient. I read the article on this site that says 1:1 mapping of indoor to outdoor unit is the best, but I really can’t fit 5 outdoor units outside! At max I could fit two outside units. So I’m wondering if having one outdoor unit for the two indoor 1st floor units and another outdoor unit for the three basement units is better, but I want to optimize my spend and prefer one if it will work just due to outdoor space issues.
Sorry for the long-ness of this, but I’d appreciate any help you can provide. Why do you think the Mitsubishi rep is advising against this? I’ve yet to find a contractor that I feel knows more about this than I do, so it is troubling… if you know of anyone in the Boston area, that alone would be very helpful to know! If you think different equipment will work better, please let me know!
Snips of the first floor and basement layouts are attached with my crude drawing of the plan.
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