I am going to be putting a mini split in my finished attic. I will need a 12k model. They are available in both 115v vs 230v. The only difference I have found is that it might cost a little more to run the 115v as far as the cost of electricity. Thats not a huge concern to me because it is just going to be a guest bedroom. It would be easier for me to just run 115v to the unit so should I just go with 115v or is it worth it to run 230v? My gut says something that is going to pull that kind of power will be better to use 230v but I don't want to waste my money on 230v if I don't need to. Thoughts?
115v vs 230v minisplit
- Thread starter Steven JP
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DIYorBust
Active Member
I think the biggest advantage of the 230 is you'd be able to upgrade to a larger machine in the future if necessary. I'd also consider whether there is room in your breaker box for a double pole breaker. At the end of the day, the wire and breaker might cost a little more, but running the 240 circuit is not really too much more work, so you might try to negotiate with your electrician. Otherwise, if it's just a simple project, and you know you're never going to upgrade it, then go ahead and run the 120 and call it a day.
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Why do you think it needs a 12K? Is the attic space completely uninsulated or something? Did you run a Manual-J load calc? In insulated houses with low-E double-pane windows the design cooling loads of most bedrooms in Virginia would be under 8000 BTU/hr, even on the top floor. Even an insulated 400' attic with crappy R19s in the head-banger cathedral ceiling, and R13 in the kneewalls and clear glass double panes is still likely to come in under 8000BTU/hr.
Many/most 12K mini-splits can deliver more than 12K of cooling at the AHRI test temperature of 95F outdoors. A cheap 12K mini-split might have a minimum modulated output that's even above the DESIGN cooling load, and well above the average cooling load, which leads to lower comfort and poor latent load handling.
Try running a CoolCalc or LoadCalc on that attic zone, using aggressive (not conservative) assumptions on the air leakage, R-values, etc. It's more comfortable to have a slightly undersized mini-split than a 2x oversized mini-split, and even those tools are going to overestimate reality by a double-digit percentage. I've seen LoadCalc overshoot by more than 25% on some rooms, even with conservative inputs, but it's still WAY better than a WAG, or some idiotic "xxx feet per ton" rule of thumb.
As for the operating voltage it really doesn't make much difference- only larger units would benefit much from 230VAC. Most 3/4 ton 115V minisplits can run on a 20A breaker, drawing less than 15A. eg, The 3/4 ton Gree Vireo draws 12A and calls out 20A overcurrent protection, the 1 ton Verio draws 17A, calling out 25A protection. Many 1 tonners might pull 20A and need a 25A or 30A breaker. eg The popular 115V Mr. Cool DIY 1-tonner calls out 20A wiring, 30A fuse. The peak amperage and breaker requirements are usually spelled out in the installation documentation somewhere- DON'T SKIMP on wire sizing, and don't oversize the breaker.
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DIYorBust
Active Member
Faster cooling might be a reason to oversize the unit? Let's say you typically spend one hour up there every time you go into that space, you might want to be able to cool it down fast and then turn it off rather than run it continually.
Well I have gotten alot of different quotes and talked to several different DIY mini split companies. I've gotten different size recommendations. Pioneer told me that the units are able to size down for the appropriate space. Seeing as this is an attic and I don't have room to do r 38, just r 30 in the sloped ceilings the extra cooling power might be useful. Id rather have it and not need it than need it and not have it. They assured me that short cycling would not be a problem. There will also be a bathroom up there and I plan on conditioning that space with this unit too. I will have the unit blowing straight towards the bathroom. It is also going to be a guest bedroom so it will not be running all the time so if I need it to cool fast like diyorbust said I can cool it down fast when i need it. I still have fact checking to do as far as size and brand but if I can do 115v that will save me from having to clear more space in my panel. Thats what I've come up with no far.
WorthFlorida
Clinical Trail on a Cancer Drug Started 1/31/24. ☹
What is detrimental to AC motors is high current. The higher the voltage the less current needed. If a 120/240v option is available on a motor, alway go with 240 volt. Power consumption is nearly the same but motors do run a little more efficient at 240 volt. FYI... most or all mini splits are Asian made and most of the world runs 220v volt single phase.
North America and Japan are 120v. For 220-240 volt it is two phase (plenty of arguments what phase meaning is) but we are L1 & L2 with each hot leg out of phase. The rest of the world it's L1. Cost to go to 240 volt is probably $50. NMC 12-3 instead of NMC 12-2. If you look at the specs, the cassettes are probably 120v only since it is only a fan motor. It's the compressor where the option may be.
From a google search: Why is 240 volts more efficient?
Higher voltage means less current and thinner wires. Thinner wires and less current means that more wire turns are required to generate the same magnetic field. ... The downside is that high power appliances like a clothes dryer would require too much current at 120 volts, so 240 volts is still required.
North America and Japan are 120v. For 220-240 volt it is two phase (plenty of arguments what phase meaning is) but we are L1 & L2 with each hot leg out of phase. The rest of the world it's L1. Cost to go to 240 volt is probably $50. NMC 12-3 instead of NMC 12-2. If you look at the specs, the cassettes are probably 120v only since it is only a fan motor. It's the compressor where the option may be.
From a google search: Why is 240 volts more efficient?
Higher voltage means less current and thinner wires. Thinner wires and less current means that more wire turns are required to generate the same magnetic field. ... The downside is that high power appliances like a clothes dryer would require too much current at 120 volts, so 240 volts is still required.
No need for neutral when running the 240. So both can use NMC 12-2. You knew that.
DIYorBust
Active Member
You need the 240 breaker though.
DIYorBust
Active Member
So for bleeps and giggles, I asked the electrician on a project I'm working ons how he runs the 240 circuits. He said he always runs the neutral wire along with the circuit. Apparently some appliances do need the neutral, and the cost is usually little for the extra conductor. I don't know if that's commonplace, or just his thing.
WorthFlorida
Clinical Trail on a Cancer Drug Started 1/31/24. ☹
I prefer -3 wire since the BLK and RED are the hot leads. WHT, unless marked, a DIYer might think it is always a neutral. Electric dryers require a neutral since most motors for the blower are 120v. For electric ranges it's needed to run the electronics. Both are now four prong plugs since the NEC 1999 edition for new work.
Jadnashua
Retired Defense Industry Engineer xxx
An oversized a/c unit might cool the area down quicker, but for maximum comfort, you usually want the air drier, and there, an oversized unit fails, sometimes miserably. You'll be comfortable at a higher temperature if the air is dryer than colder and damp...an oversized unit does not need to run as long, so it does not remove as much moisture each cycle. A two-ton unit for a single room seems like way overkill...costs more to buy and less comfort.
DIYorBust
Active Member
True, but I think most of the mini splits now are variable speed "inverter" units that can ramp down to match the cooling load.
Very few mini-splits use AC motors. Even the low-cost DIY units are all using inverter-modulated DC motors for the compressors, and usually for the blowers as well.
Actually Japanese grid is nominally 100V /60Hz (sometimes dropping into the 90VAC range) in the southern/western prefectures, and 100V/50Hz the northern/eastern part, with some prefectures that have a mix of both. 200V-250V is sometimes available in some areas, but the residential wall plugs are the same independent of voltage or frequency, making it too easy to plug stuff designed for 100V/60Hz into 200V/50Hz sockets (and conversely). The voltage and frequency divide makes it far more difficult to deal with power imbalances between one end of the country, since there is only a very limited capacity in the asynchronous converters tying one side to the other.
There is no real correlation between floor space and cooling load. An R30 cathedralized ceiling doesn't significantly increase the cooling load relative to an R38 roof of the same size- the window solar gains are a much bigger driver. (Even the color of the shingles makes a bigger difference on peak cooling load than R38 vs. R30.)
It's just stupid to install a modulating system that is so oversized that it usually just cycles on/off at the minimum modulated output, but that sometimes happens when following brain-dead "square feet per ton" rules of thumb. Some one-tonners can't throttle back to under 5000 BTU/hr, which may very well be the design condition cooling load of that space.
Almost all of the newer Pioneer mini-splits are now re-labeled Midea units (which is a good thing- some of their older stuff was pretty junky by comparison). But when comparing apples to apples, keep a sharp eye on the MINIMUM cooling output. Some 3/4 tonners can't throttle down as low as some other 1-tonners.
[edited to add] Curiously, the 1-ton Pioneer throttles back to 3700 BTU/hr making it more appropriately sized for that tiny space than the 3/4 tonner, which won't back off to less than 5800 BTU/hr, which is probably close to or more than the design cooling load. This is true of both the 115V and 230V versions. Their 3/4 ton units have slightly less than a 2:1 turn down ratio between min & max cooling output compared to a 3.5 : 1 turn down for the 1 ton. This is not typical. [end edit]
The difference in how fast it cools the space is a function of it's maximum cooling BTU rate not it's AHRI "rated" BTU/hr, which is the modulation level at which it's SEER efficiency is tested. They are sometimes the same, but often not. There are many 3/4 ton mini-splits tested at 9000 BTU/hr for it's "rated" output that will deliver 12,000 BTU/hr at max speed under AHRI test conditions, and others that don't. But in either case, you probably won't detect much time difference between a 3/4 ton and a 1 ton, the way you would notice a cool-down time difference between a 1 ton and 2 ton.
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Fitter30
Well-Known Member
Minis run 24/7 not the condenser but the indoor unit. A watt is a watt doesn't matter if the seer rating is the same between 120 or 240 volt they use the same amounts of watts.
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