Pros: Low profile, versatile, efficient, quiet, heating and cooling options, and technologically proven over the years.
Cons: Cost of system and installation, requires trained installers and service technicians.
Mitsubishi (Mr. Slim brand name) is only one of several companies currently offering these styles of "ductless", heating/cooling systems. Although Mitsubishi has been at it longer than many of their competitors, originally starting up their operations in 1870.
To truly understand what is different about these heating and cooling units, and the array of applications they fit into, you need to understand, they are stand alone systems. They are designed as two major components, an outdoor condensing unit and an indoor wall or ceiling mounted evaporator/fan powered, air handling unit, which discharges the cooled or heated air into the home.
Before these products were introduced to the market, your only choice to add cooling to a room was a window mounted unit, what many of us in the trade refer to as a window shaker. Then, for heating a baseboard or wall mounted supplementary heater. Unfortunately, the window shakers haven't totally lost that reputation for being too noisy for bedrooms, because the compressor and the discharge fan are in the same room. In addition, window mounted units have been an easy source of illegal entry to your home by burglars over the years and they block out a good portion of the view you would normally have.
On the upside of the ductless split systems, you can hardly tell when they are running, thanks to the fact that the noise producing compressor and exhaust fan is located outside. The outdoor unit can be located from 25 to 49 feet from the indoor unit for versatility and in convenient hidden locations in the garden or around the back of the house. The indoor air handler has a multi-speed fan, controlled either automatically or by remote control to maintain the comfort levels without the noise.
To be honest, when I was first introduced to these products in the 1980's, I dismissed them as a niche market product, suitable for motel rooms or small office applications. Over the years I have come to appreciate that they are much more than that. In the mid-90's I was faced with a challenging design application to cool an old large church with a boiler heating system. It was clear that there was no way to install sheet metal ducts or a massive roof top commercial cooling system, without destroying the aesthetic beauty of the interior and exterior of the church. My solution was to turn to the use of several of these units, strategically located around the interior of the church walls. Disguised by wooden slatted enclosures. The minister responsible was concerned about noise from the indoor units which might distract from his sermons and we had to take him to a test unit to demonstrate the quietness of the indoor air handler before he agreed.
The overall cost of the installation was comparable to what a commercial rooftop unit and the added construction costs to install it might have been. Similarly, I have found that by the time we add in ductwork additions in difficult locations, these units sell themselves on installation costs alone.
The minister now believes the attendance of his parish has risen during summer months and with the indoor units disguised on the walls and the outdoor units surrounded by hedges, you would never even know the place has air conditioning. This church ended up with 10 air handler units around the walls of the church interior, located about 10' from the floor, which cycle on and off independently, as required to maintain the comfort levels set. Including those hot summer days when hundreds of people are adding their body heat to the cooling load.
Since those days, I have seen them installed in condo's, townhouses with baseboard electric heaters, or hydronic heating systems (boilers) renovated homes with additional rooms, cottages, motels, historically designated homes and even new home construction. Sometimes the advantage added is in using two or three small units to cool and heat zones within the home or the building without having to crank up the full load of a larger unit unnecessarily. So they can actually save money over the costs of upgrading ductwork, furnace fans, and chasing them in.
As for installation, they are one of the easier systems to install. The outdoor unit is located, wired and connected to the indoor air handler through a small hole in the wall or ceiling (about 3-4" in diameter) for the refrigerant lines and wiring.
While they are more expensive than a window shaker, they do not keep you awake at night, are generally much more efficient, can offer the option of supplementary heating, by reversing the flow of the refrigerants and becoming a heat pump, that window units generally don't, they look better, do not reduce security at windows, do not block out the view. This model is about 3 feet wide, 7 1/2" deep and 11" high and looks as sleek as it sounds.
Mitsubishi also make a series of these for cooling only that can be connected to three indoor air handlers from one outdoor unit to cover other rooms at a lower cost than multiple complete units. All can be independently controlled by a hand held remote from whichever room they are in.
One of the hidden advantages of this technology is that the compressor does not turn off and on as conventional cooling systems do. We've all heard the sound of our refrigerator compressor kicking in and cutting out or the rattle of a window unit kicking on and off. The Mitsubishi
compressor slows down and speeds up according to the needs of the room, so it draws less power and prolongs the life of the compressor.
This can no longer be considered as new technology, as thousands of them have been sold throughout North America over the past twenty years and many more of the big manufacturers have launched similar designs. I feel more comfortable recommending them, now that there are more technicians out there with factory training for installation and service requirements, than I did twenty years ago.
You need to study the entire range of the product line to determine which model best suits your application. I always recommend having a heat loss/gain calculation done to ensure you are sizing the system to meet your needs. The end cost will depend on whether you want heating and cooling or cooling only, the Btu's required, how many rooms you need to serve and the required length of the refrigerant bearing linesets that connect the indoor unit(s) to the outdoor unit.