Update. The unit was excellent this year. My guessitmate was between $300 and $350 on heating from oct to may. It was still making 110 degree heat at -9 . I did notice the rest of the house was chilly when it was around zero. The defrosts every 45 to 55 min were noticable when it was that cold Anyways that got me thinking about adding another unit to help ease the work during the single/teens temperatures on the unit and having extra heat. The only problem I do notice is since my unit I have know cycles too much when its in the 50s so a smaller unit for heating with a smaller low end heat would help, I am not worried about ac end since I was able too use one 5000 btu and sometimes two 5000 btu units to cool the house before. So I've been looking and seen the MSX muti zone units are out and new single units are out. First basement has not heat and stays in the middle 40s in the winter and around 64 ish in the summer. There a lot of mositure and a dehumidfier doesn't really work well until mid summer. The rafters are insulated (r13) and some of the walls are too. Anyways I was thinking of possibly adding a air handler down there for heat either a .75 or 1 ton. The main floor (drawing above) I was debating on a unit in the dining room (.75 ton) to heat the dining room and the kitchen. The kitchen was 60 during the negative degree days with the radiant heat set at 60. When it was in the upper teens it would stay around 63. Then the spare bedroom I was thinking of putting a .75 ton unit to blow out to the hallway and push air to the bath room and bedroom. The spare bedroom was set to around 50 with the radiant and the door shut while the other bedroom I used a box fan to push the cold air down the hallway and the warm air would enter above. I'm debating on heating the basement and if I do `I was think a 20,000btu dualzone for one area on the main floor and one down in the basement or do a 24,000btu tri zone and heat all the areas listed. Or I could do one of the single zone units (FH9000btu) and just heat the basement area or on the main floor since they are the most cost efficient though.

Assuming your looking at inverter model mini splits there's no problem with oversizing somewhat as the unit will "throttle back"...reduce compressor output and air handler fan speed to meet the heating or cooling needs being called for. This is unlike typical AC/Heat pump systems that are either on or off and when oversized in AC mode may not allow the room to dehumidfy enough...so no problem oversizing with a mini split as long as it's not grossly oversized. Also,many mini split heat pumps can exceed their nominal rated btu's in both cooling and heating...so a rated 18,000 btu in A.C. mode might be able to put out 20,000 btu. You'll need to check the specifications carefully to find this out but many models nominal ratings are actually lower than maximum actual output capability. It's been my obeservation that a mini split will provide more cooling and heat for it's rated size than a typical ducted system. As there are no losses due to duct work in attic or in crawl/cellar space you get higher efficiency not just in energy ratings but in actual output when comparing the similar size traditonal system. Also, you might want to check out a few other brands of mini splits besides the Mitsubishi (which is very good one). I'd also look at Futjitsu which has 18,000 and 24,000 models that qualify for the tax rebate. Sanyo is another good one. I'd stay with the Japamese brands and only buy from an authorized dealer for the brand who has installed a bunch of them. I'd leave the bathroom door open or ajar a bit and you'd probably be OK. If you've got a lot of money you could buy an inverter model mini split that can accomodate two wall air handler units and put one in the bathroom...but that would be overkill for 48 s.f. in my opinion. I've got a 15000 btu model in my sunroom (wall to wall 6' windows) which is L shaped and 400 s.f in Columbia, SC. It does a great job even though a manual J calculation said I needed 17,000 btu. I work as construction coordinator for a facility that has 50+ mini splits so I'm very familiar with these units.

I found myself quite busy and didn't see any earthshaking new products. Fujitsu introduced a 33 seer unit however. I would think in your situation you would be better with some redundancy. Rather than doing a triple unit perhaps you should get a dual and then one of the very high efficiency cold weather singles. One system would back up the other and operate more efficiently. You can also get apps that will allow you to monitor home temps while you are...elsewhere. I use the Rinnai Energysaver for my best source of heat. It works very efficiently on lp and will restart after a power outage. 7 day programmable stat built in. Not cheap, but the very best there is and they heat much better than the minisplits

I don't see any coils of excess line in my Mitsubishi systems. The installer, who has been teaching at a local trade school for at least 30 years, must have figured out how to cut them. He must have figured out how to charge a system too since a reversing valve failed under warranty and had to be replaced. I have no doubt that older systems may be longer-lived than newer ones, and less complex. That does not mean that the stone-hatchet stuff is better in every way. If we followed that logic, we'd all be driving the cars that they still have in Cuba. Learning new techniques can be challenging and training is expensive when you consider the time needed, but it is necessary. The down side may be that it puts small shops at a disadvantage. I don't see how one or two people can afford to stay current on everything that is out there today. It is not limited to cooling either. Right now, I've been dealing with a boiler replacement at my dad's house and trying to do it on a reasonable budget. Putting a low-mass boiler in his old hydronic system (without a lot of expensive modifications) is a challenge. Finding a local installer that is up to date in his rural area has been frustrating. (Small here is really small. Katy is huge compared to his town of 2000.)