7 Comments

1. 
   nickdefabrizio | Feb 07, 2025 07:46am | #1

   Once again, a great article. Thanks! Let me share my experience with heating with mini splits.

   The House: I have a 1980 built house in zone 5. It has a 1500 sq foot main floor and a fully renovated partial walk in basement with another 1000 sq ft of living space and a 400 sq foot garage. I air sealed the attic, built an insulated hatch cover and added additional batt insulation. Otherwise average insulation and tightness. The home was heated with oil fired baseboard using an efficient Energy Kinetics boiler.

   The Mini Splits: Over a period of ten years I installed three of the high effciency 12k Fujitsu single head mini splits (two low temp rated to -13F and one to -5F). One air handler is in the basement , and two are in the main living area. I also installed a heat pump hot water heater (which I got for $750 scratch and dent at Lowes and installed myself). I bought the mini splits from an HVAC supply company that would sell to me ($2500 each with lines and acsseessories including electrical). In all cases I installed them myself (including running 15 amp 240 volt lines), but I had a friend with an HVAC license charge them up for $100 each. The time it took to install each mini split and 240 volt power line was about 8-10 hours each. I installed the outside condenser units under a raised deck so they never get snow on them but if you don't have a deck or roof, I recommend building a small shed roof to keep snow off. Also, it is best to keep them well above the snow line on a stand or wall bracket (I prefer the former to avoid any vibration to the wall). Install a surge protector on each 240 line!!

   Heating Performance: Since there are no mini split heads in the bedrooms we leave the doors open and heat travels down a short hallway. Typically there is a 5-6 degree difference between the living area and bedrooms; so we typically keep the bedrooms at 66-67F On very cold days my wife will turn on the baseboard heat for comfort. In my opinion baseboard heat is more comfortable, but I have become used to the mini split hot air system. My wife is not as sure. The garage still has baseboards and I leave the temp at 45F to make sure the pipes don't freeze. Thus, we still use some oil heat.

   Cost Savings: Before the mini splits, we typically used 700-900 gallons of oil for heat and hot water. With the mini splits and heat pump hot water heater we are now using about 100-150 gallons of oil. It is hard to say how much electricity we now use for heat and hot water because we now have an EV and plug in Hybrid (PHEV) and my wife and I drive 50,000 miles a year between us. Also we have a PV system that produces 7,000 kwh a year. But the total amount of electricity we used last year net of PV production was about 21,000 kwh (or 14,000 kwh net of PV production). We pay 10. 8 cents a kwh. So our electric bill (net of standard fees) was around $1,500, and that replaced about 500-600 gallons of heating oil and about 800 gallons of gasoline I am estimating maybe10,000kwh is used for heat and hot water.

   Mini Split Issues to Consider: I am very happy with our mini splits. However, for most people, there are several issues that need to be considered. First, the total cost of mini splits when installed by most HVAC contractors is just too high. This is exacerbated when people want an air handler in every room. I know several people who spent over $25,000 to install multi head units with indoor air handlers in every room of an average sized house. It makes much more sense when configured like I did, but not everyone is ok with leaving doors open in bedrooms and the like. I don't understand why HVAC contractors will charge a much larger per hour cost to install a mini split than installing any other equipment. The tools are mostly the same. Maybe they have more warranty issues? I suspect it is still seen as a novelty item. Ultimately Second, it is not clear if mini splits will be as robust over long periods as other systems. Certainly oil and gas fired boilers last decades and most central heat pumps will probably last 20 years. My oldest mini split is going on 11 years and still ok. However, my dad had mini splits rot out at his beach house in less than 10 years so be wary in coastal areas. Also, its difficult to get service people to fix them (I once replaced a motherboard myself on one of his units becasue no one would do it). The mentality is to throw it oout and buy a new one (hard to do when they are pricey).

2. 
   anonymoususer | Feb 08, 2025 01:44pm | #2

   Thank you, Martin, for this interesting and informative article. And thank you, Nick, for your helpful commentary. We live in a 3k square foot house and currently heat with forced hot air oil furnace. We also have a 2020 EPA certified log-burning insert in our fireplace. We use the latter when we are home for at least 3 consecutive days. Because of an unusual job, we are home a couple weeks, then out of town a couple weeks, then home, etc. This pattern holds true year round. Anyway, our oil furnace is on its last legs, and we want to replace with ductless heat pumps. We do not plan to ever cool our house in summer, as we find summer temps comfortable in our region (technically zone 5 but less than 15 miles from zone 6). For heat pumps, we are looking exclusively at Mitsubishi "hyper heat" units cuz these are common in our community. We wanted a ducted system but 2 licensed mechanical engineers came to our house (one who owns the local Mitsubishi "diamond dealer" hvac company and another who works independently): neither was able to figure how to duct a system for us, nor where to put the air handlers. So we gave up on the idea of ducted and will go for ductless. We are a big family and, unfortunately, certain adults in the household are NOT amenable to leaving bedroom doors open at night, nor to having small wall openings that let warm air pass from common areas to bedrooms. So we will need an air handler in each of the 6 bedrooms. Plus 1 in kitchen, 1 in living, 1 in den (all 3 of which are far from each other, but we spend roughly 1/3 of the day in each of these 3 rooms). So a single zone system will not be possible. We will likely need at least 2 multizone systems. The entire house is currently fully gutted cuz we hope to soon undergo a deep energy retrofit. I hope our being gutted will make it easier for whatever hvac contractor we choose to install the new heat pump system. Anyway, in a heating only context, what complaints do people have about multizone? I remember Martin Holladay or Allison Bailes or Randy Williams or Jon Harrod (I forget which GBA writer) saying it's better to have multiple single zone systems vs multizone but I cannot remember why multizone systems are considered problematic? Notably, our local Mitsubishi "diamond dealer", who holds a mechanical engineer license (we looked him up), told us he heats his personal house with TEN single zone Mitsubishi hyper heat ductless systems. Yes, TEN. When we asked, "Why didnt you install 2 or 3 multizone systems instead of TEN single zone?" he ignored us and changed the subject. I cannot imagine having TEN compressors outside a single family home, even if there were, say, 3 along the north exterior wall, 3 on the west exterior wall, 2 on the south, 2 on the east, etc. Aesthetics aside, it just seems silly. So can someone please remind me why single zone is better than multizone? If I could talk my family into having a more "open" house, with plenty of wall openings, that would be great--we could heat house with a few single zones. But this idea is not flying with the teens nor elderly, so it will need to be multizone. What caveats can you offer that are specific to multizone ? As stated early, we will only be using them to heat house, never to cool. Thank you

1. 
   charlie_sullivan | Feb 08, 2025 03:19pm | #3

   Have you considered ducted minisplits? You can have one sitting in the attic or the top of a closet with short (a foot or two) ducts to feed several adjacent bedrooms.

   Two issues with multi-splits are: 1. They typically don't modulate down to as low a speed, so you end up cycling on and off rather than running continuously at low power. 2. They are more complicated to specify and install correctly so sub-optimal installations are common.

   If you can find someone willing to do hydronics, air-to-water is a great solution to the problem you describe. You can have small, low-output "heads" or simple radiators in every room, without needing oversizing.

1. 
   anonymoususer | Feb 09, 2025 11:43am | #5

   Thank you, Charlie. Unfortunately, our house is laid out in such a way that only 2 of the 6 bedrooms are adjacent to each other. Floor plan is very spread out because long before my time, someone decided to do addition after addition. I will look into hydronics, as Im not familiar with those. I did purchase ceiling infrared panels for small rooms such as the vestibule and our 4 tiny bathrooms.

2. 
   nickdefabrizio | Feb 08, 2025 08:46pm | #4

   One thing I learned is that trying to get to 100% heat using mini splits can be much more difficult and expensive than getting to 80 or 90% from mini splits. In your case, if your existing duct system is in reasonably good shape, you might want to consider an efficient central heat pump with a gas (or propane or oil if no gas) back up. Bryant and Carrier (Greenspeed) make good units that will handle a significant part of the load. They are not rated for temperatures as low as the high quality mini splits are rated to, but bear in mind that in zone 5 most days are well above rock bottom temps.

   Another approach you might explore is to install a central heat pump with gas (oil or propane back up) furnace and put one or two very hig efficiency single mini splits in the main rooms. This would provide a significant portion of the heat in an efficient way. At night when people want to close bedroom doors, the ducted central system would provide heat to the bedrooms. This is sort of like what I have with the bedroom baseboard in my home.

1. 
   anonymoususer | Feb 09, 2025 11:52am | #6

   THank you, Nick. Unfortunately, our existing ductwork is improperly sized, in so-so condition, and largely enrobed in asbestos wrap, even in areas that were exposed prior to our gutting the whole house. Im not surprised to read that it's tough to get 100% from mini splits, since each Mitsubishi compressor I looked at only runs at 100% capacity at 47 F; at 17 F and below, capacity drops to maybe 70% of nominal. Precisely what we are looking for is equipment that can heat the house at temps where our log-burning insert cannot. We considered heat pump with oil backup (we have never had propane) but decided we wanted to move away from on-site fossil fuels, even though the plant our electricity comes from is largely powered by fossil fuels and nuclear.

3. 
   anonymoususer | Feb 09, 2025 11:58am | #7

   A kind GBA reader recently warned me of a well-documented problem with ductless splits that are multizone (as opposed to single zone): because they're unable to modulate down to low speed, they end up cycling on and off rather than running continuously at low power. Im wondering, is this less of a problem when there are not very many heads (yet still greater than 1) being served by each compressor ? For instance, which will cycle on/off more: a) one 40K compressor serving 8 indoor heads versus b) two 20k compressors, each serving 4 indoor heads ? Thank you