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We are in the process of adding an AC system to the top floor of our old home (on the mid-Atlantic coast). Standard AC systems (with ducts) are not an option due to the configuration of the house/rooms with no realistic ductwork space. We have been told that a ductless mini-split system would be suitable for our home. However, I have one main concern about this. The floor on which we would be installing this system is fairly chopped up due to numerous walls and doors. I know that the min-split systems are designed to accommodate various zones but can one unit appropriately cool, say, two smallish bedrooms that are across the hall from each other? We would have three units installed on the floor but I am still stuck on viewing these systems as “permanent window units”, so to speak. A standard window unit can easily cool one room (and even make it very cold) but the air doesn’t flow well into other rooms, leaving one room very cold and adjoining rooms very warm. Do the mini-split systems (with inverter technology) truly work differently? In short, would we basically have a permanent window unit that will make one bedroom very cold while the bedroom across the hall is warm? Or does the inverter technology change the ability of this system so that air flow between the rooms can effectively cool both? We also have transoms that can be open at all times, as well as doors directly across from each other that could be open during the day. The cost would prohibit having a mini-split unit in every room, as there are four bedrooms and a number of other smaller rooms.
 

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A ductless split system (like WLCG/WLHG by EMI) is basically a window unit without the window. Only time I use them is too cool an area that has no barriers. If you close a door the area cut off will not get much cooling. Transoms on the top and bottom will help with some air flow
 

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Have you looked into a high velocity system yet. The duct work is very small, and doesn't take up much space.
 

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Hvactech, when you state “multi zone mini split systems”, are you referring to simply having a mini unit in each room, thus giving each room its own zone? Or does it go beyond that? Basically, we have a floor with four bedrooms, a few bathrooms, and a couple very small open areas. We are contemplating putting a mini unit in three of the bedrooms. But I am wondering if one of the units would be able to cool one bedroom and a bedroom across the hall (doors and transoms directly across the hall from each other) while the two remaining units would need to cool not only their respective bedroom but an adjoining bathroom. As mentioned, I’m stuck on viewing these systems as permanent window units and wonder if one unit can truly cool two bedrooms across a hall from each other using the inverter technology, without having to install a mini unit in each and every room. Would the one bedroom be freezing while the other bedroom doesn’t even feel cool?

Beenthere, we looked into high velocity systems upfront but due to the configuration of the house ductwork of any size would either ruin parts of the home (specifically two dormers in the center of the home) or the ductwork would have to have multiple 90 degree bends. That sounded like a great system if we could have worked out the ductwork, but three separate companies have failed to figure out a way to do so. It’s a very old, oddly-designed home. In short, we’d either have to build a box going across the center floor of the dormers or we’d have to go along the roof line, putting 90 degree bends in the ductwork. One option is aesthetically and practically unappealing while the second option would drop efficiency down to a very low percentage (if it would realistically function at all). The joys of owning an old home, eh?! LOL Thanks for any suggestions if anyone has any.
 

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Check out Mitsubishi coaster. We did a job last year that ran 8 evaps off of a singe condensor . I think you'll want all the bedrooms to have one or that last room will be uncomfortable.
 

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Thanks for the information. From what has been said here, it sounds as if a mini-split system provides basically the same air conditioning as multiple window units. At this point, I may just stick with a window unit in each bedroom as the cost of all of these window units combined is less than basically just one mini-split (and I would need at minimum four mini-splits). I can’t see the benefit of spending thousands of dollars for what ends up being a wall unit for every single room. Am I missing something as to the advantages of a mini-split system? Thanks again for all of your responses.
 

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Main advantage of a mini split is that you still have your windows to look through.
 

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Am I missing something as to the advantages of a mini-split system?
depending on your heating situation A heat pump mini will provide heat as well. Not near as ugly as window unit. much more efficient. remote controls and temp settings vs on or off.
 

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Another advantage is that the ductless is QUIET!!!!
What'd you say? I turned off the window-shaker so I can probably hear you now:wink:

I found an interesting paper yesterday:

http://www.nrel.gov/docs/fy11osti/52175.pdf

One thing that I did not figure out until after I owned three outdoor units driving 7 indoors in my house is that the single-to-single models probably throttle back more effectively than the multi outdoor models. One of the take-home messages that can be deduced from that is if you are installing a multiple or multiples and a single is that the single should be placed in the room that will be at low output most, probably a bedroom.

Keep in mind that high-wall indoor units are one of a few options. You can get ceiling-mounted, small air handlers that can serve more than one room and floor-mounted models.

As the article points out, significant savings can be gleaned by the inherent zoning. That is a feature that was very influential in my decision. Some disadvantage are, no way to incorporate central humidity control or central fresh air.
 
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