Hello, Would like to know how many BTUs (for 1 wallmount system)would I need for two floors of 690 sqfeet (each floor). The Unit will be on the 2nd floor in the middle between 2 bedrooms and a washroom (over washroom door facing master bedroom). It will be a dual split system. ------------------------------------- Also would like to know which is a safe reliable cost efficient brand, example of wall mounted (split systems) air conditions I've heard of: Fujitsu (they give 10 years warranty parts and labour) Mitsubishi (6 yrs parts and labour however been making them longer) Daikin (6 yrs parts and labour) Igloo York Carrier Grey All about the same price... ----------------------------------- Finally, is it better to get a dual system (with heat pump), from my understanding they are almost the same price and the advantage is that it has a variable BTU which may save some $$. Since the heat pump will be at the higher level then it wont heat as much however it is coming at about the same price. Then again more electronics in a system more chances of malfunctioning sooner? Thank you, Stelios

Im not sure on your setup or how many btus you would need. You could get a load calculation done. I didn't get one but figured my own and also looked at my electric usage and figured out the estimated btus. On the number of condenser; It depends if you don't mind the condensers outside the house. You will also have to keep them up out of the snow. Google how to buy a ductless mini split. It a good write up . Also if you do the floor mounts You can run the lines in the basement and to the outside. You also will need a drain in the basement or somewhere outside to drain the condensation pipe from running ac on it also. The problem I had with the ducted units is how far to run them and trying to figure a return since I was doing some of the install.

My perception about uneven heat or cool from mini splits is that the former is more of a problem. I live, however, in a raised house with cold floors and it might not be so bad in other situations. Part of the issue is that as the set point is reached, the blower slows down considerably. I am looking at data that indicates it drops to about 1/3 of the highest air flow in some Mitsubishi units. Under conditions near the set point, there is considerably less mixing of air in the room and lots of opportunity for thermal stratification. They make good ceiling heaters. In heating mode, or in dehumidification mode, I always have ceiling paddle fans going in the rooms that I have them. It fixes the problem. Air conditioning does travel through walls to some extent. Structures vary a great deal in this respect. If you have a well insulated and air sealed home, the heat and moisture transfer rate between rooms is much higher than through the exterior walls so more even conditions will occur. In a poorer structure you will see a larger temperature differential between rooms with heating and cooling sources and those that do not. That is why zoning does not save you much energy in good structures. Accepting all that, no, you can't get the performance in evenly cooling a whole home with the most common type of mini splits that you can with higher static pressure ducted systems. That said, I like the way mini splits work in a home. A typical summer weekend day with both of us around goes like this in my house. Wake with one bedroom unit going powered by an outdoor unit supporting two. The door is open so the rest of the house is getting some cooling. It is not uncomfortable anywhere unless you start doing push-ups. The high wall unit is running at low capacity and mostly dehumidifying. Hit the kitchen for breakfast. If a lot of cooking is to be done, turn that one on. Outside to do work in the cooler part of the day lots of times for me, but come in for exercise sometime in the AM and turn on another unit in that room. The remainder of the house is still pretty comfortable. As we move around the house and heat load keeps increasing, we may have 4 of 7 going, but probably more like 3 at a time. We have a mix of 6000 and 9000 btu high wall units. During the course of the day we have gone from running less than 6000 btu to a theoretical max of maybe 30,000 btu, but those 3 or 4 units are not running anywhere near full capacity. They are really sucking the water out of the air so the indoor temp is probably above the design temp and comfortable With humidity in the low 40s. We have a total of 51,000 btu. The only time I've ever run it all is for fun, coming back from a trip, or If I forgot to set them to come on in the afternoon. It has been a long time since I reviewed the data. Total heat loads for the house look like about 31,000 btu and install "recommended" 38,500. I guess the difference is a safety margin. In hindsight, I should of convinced the contractor to skip the 9000 btu units. That would have dropped us back to 42000 btu and would have been adequate. What we have works due to variable speed nature of the systems. They run at highest efficiency at part load and that is notable. I often tell people that if you are happy with the cooling you get from window units, mini splits will work for you. For similar reasons, I think that they are a great solution for a home with nice hydronic radiant heat in an area where not much cooling is needed and the homeowners don't want to lose the hydronic. If a person in Japan has 300 sq ft, that is 1200 square feet for a family of 4. That is not shocking to me. I am looking at one source that says 300 per person is what the US had in the 1950s. Below is another source that is fun to look at.. What is driving the increase, larger homes or smaller families. The answer is both and the magnitude of the effects is different in different eras. The biggest problem that I see with mini splits is not big rooms because you can always make a bigger one or add a second unit. There are even good controls for two in one area. The biggest problem is installing low enough capacity since the smallest are 5000-7000 btu depending on manufacturer. Yes ,the variable units throttle back to about 30% of that, but that is the compressor so with more indoor units ganged on a single outdoor unit means not as much modulation and more bang-bang operation. That means in a place with smaller rooms (Japan), mini splits should be a bigger problem than in places with big rooms (USA). The inability to hit low enough capacity with a unit in each room is part of the reason for the higher cost, you will be over capacity no matter what you do unless you have very large rooms. https://www.propertyshark.com/Real-Estate-Reports/2016/09/08/the-growth-of-urban-american-homes-in-the-last-100-years/

Mini splits are best suited for 'spot cooling & spot heating'. If you don't consider all 'spots' in the structure then you will have hot spots and cold spots within the structure. While 1200 square feet isn't all that large it's large enough to pose challenges to mini split design. What does comfort mean to you? That's the whole reason we put systems in our homes to be comfortable. It's one thing to be in your living room, quite another to be in the bed room trying to sleep. You spend 1/3 of your life in the bedroom sleeping. If all you had was one room in your house, mini split would be more practical solution. The more rooms you heat and cool, means more heads you need to heat an cool. The more equipment you have, the more maintenance, breakage and so on. This is why ducted HVAC systems are best for a house.