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mini split options for addition?

first off i am still trying to figure out how to attach my drawing- sorry-
puitting up an addition, single story with cathedral ceilings conventionally framed- no trusses. the overall is 20' x 40', with 1 room 20' x 22', another room 15' x 18', and a bathroom with a closet at 5' x 18'.
i am thinking using a mini split system for cooling and heat but dont know if i should put in one large one with 3 zones or 1 med one for the big room and another medium 2 zoned 1 for the other 2 rooms (bed and bath). i am having a hard time getting an answer from the hvac contractor- he says i will put in what you want.......

Re: mini split options for addition?
Re: mini split options for addition?

Mini-splits require an air handler (evaporator & room blower) for each walled off space - - each handler is a "zone".
You definitely need 1 handler for the 20x22, and leaving the door open to the 15x18 room won't be enough to cool/heat it - - thus, you'll need 2 handlers. The bathroom at 5x18 will be like any space not heated or cool - - if you put in an air handler, it's will be an overkill as the minimum capacity is about 9,000 BTU. If you go with 3 handlers (with 1 outdoor condenser unit), the hardware is about $3500, and when you add in professional installation and maybe some main panel work (1x 240v and 3x 120v circuits), you're well over $6,000 all-in.

Also, I think mini-split heat/cool can heat down to about 35 degrees outdoors. Check the manufacturer specs on outdoor temperature for heating to assure that it works for your area weather.

Look into mini-duct, like the UNICO system. I think the TOH website has some short videos on this. Mini-ducts are, I think, very expensive systems. I've seen flat-roof installations for about $15,000 plus a new foam roof ($15,000) over the mini-ducts.

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