What is the name of each of these three formats (or form factor) of air source heat pump outdoor units?

  1. LG LMU300HHV - Variable speed, 4 zones, 30 kBtu, 20 SEER


  1. LG LMU480HV - Variable speed, multiple zones via branch box, 48 kBtu, 19.5 SEER


  1. Trane XV18 - Variable speed, multiple zones via branch box, ?? kBtu, 18 SEER

Trane XV18

Common denominator

Tried to get models that are relatively close in terms of functionality. It's understandable that larger models can have more capabilities but I'm posting this to try to factor this out, and get the name of the form factor.

Ducted vs ductless

Some manufacturers label their heat pump as ductless but how do they know if I'm using ducts or not? Or is a ductless heat pump referring to the usage of refrigerant line-sets to indoor fan coils? Isn't that 100% of all the heat pumps though? There doesn't seem to be a type of heat pump that directly cools or warms the air then pushes that air straight into ducts in the home. So it can be concluded that ducted vs ductless refers to the overall system, and has nothing to do with the form-factor of the outdoor unit.


Seems like some people tend to apply the word 'mini-split' to the first one but from my research mini-split just refers to the fact that each indoor unit services a single room instead of the whole home. Seems to be a catch-all that covers both 'single-split' (1 outdoor unit, 1 head) and 'multi-split' (1 outdoor unit, 2 or more heads) as long as the rooms being serviced are separate. So again, words like 'mini-split', 'multi-split', and 'single-split' refers to the overall system, and has nothing to do with the form-factor of the outdoor unit.

Inverter vs something that's not an inverter?

I was tempted to name the first two "inverters" and the Trane model an "older non-inverter" but according to this site the old Trane form factor is also an inverter.

Asian-style heat pump?

One potential candidate in the factor of the naming is that the first two styles I posted above from LG appear to be very common among Asian-Pacific brands such as Daikin, Mitsubishi, LG, Samsung, Fujitsu, etc. That is not to say that North-American manufacturers don't also have this form-factor (Trane has the XV19 in this form-factor) but they don't seem as common.

Reiterating the question:

How do you name these three different forms of heat pumps?

2 Answers 2


There isn’t a formally defined naming scheme that is consistent throughout the industry.

That having been said, the entire system would be called “ductless mini-split”. It has multiple components: an outdoor inverter compressor heat-pump, the refrigerant line sets, the indoor head units.

You’re correct that you could hook up one of those outdoor inverter compressor heat pumps to a line set that actually connected to a ducted air-handler with coil inside the home. In that case, you wouldn’t have a ductless mini-split system. You would have a forced-air heat pump system.

There are also other kinds of heat pumps. The most common ones that people associate with ductless mini-splits are called air-to-air, they also make air to water, water to air, and even water to water heat pumps.

A “heat pump” works like a refrigerator, except the inside of the “fridge” is your whole house. It acts as an A/C like a fridge cools its contents. If you run the refrigerant lines in reverse, it heats your house just like the fridge generates heat on the back and sides as it cools.

That Trane unit seems to only operate in cooling mode. It might also be a single zone system — which really just means only connectors for a single line set — which would mean it’s meant to be used with an air handler and coil inside the home. But it’s really fundamentally the same in terms of the physics of the LG heat pumps that you would normally use with a mini-split system.

  • Thanks for the answer! How do you call those three different form-factors of the outdoor inverter unit?
    – Daniel
    Jul 16, 2022 at 20:36
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    @Daniel perhaps something along the combination of AC outdoor unit, vertical fan, horizontal fan, dual fan
    – jsotola
    Jul 16, 2022 at 20:47
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    I don’t think there’s a formal naming scheme in fact. I think you should start with the limitations that you have and the desired overall system type (ducted vs ductless, etc) and then find the right model based on that. I think it’s a sign that you need the help of a professional HVAC installer if you are starting with form factor. Start with your heating and cooling needs and work backward from that. Jul 17, 2022 at 0:25
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    TBH, your best bet may be to simply show your HVAC contractor(s) pics of the style you're after and have them give you options. As noted, there probably isn't a formal naming scheme, so it gets down to "point and grunt". ;)
    – FreeMan
    Jul 28, 2022 at 17:55
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    Ah strange, the timing made it look like you did. Regardless thanks for updating your answer. I've marked it as the accepted one. Thanks!
    – Daniel
    Jul 28, 2022 at 18:17

The big train style unit is an older style (prior to inverters)

The Flat style are usually mini split or ductless but not always the newer replacements of high efficiency ducted systems with only a single zone may look just like this but boast efficiencies +18 up to 23 where the old systems big square were common as a 13 for the seasonal efficienc(higher is better)

  • The high end right now is 38 SEER, but that may require the "mini-split" form factor. Jul 17, 2022 at 3:19
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    Yes high efficiency condenser coils and inverter/ vfd compressor control are the main differences, inside the mini splits have no ductwork to heat and cool it all goes into the home less a tiny loss on the line set. I am not sure if the latest and greatest efficiency ever pays back , today the high efficiency central air is upper teens to mid 20’s. Todays less expensive units run 15-18 seer, 10-15 years ago they were top of the line. So the efficiency gains end up reducing the cost over the years, mini splits run higher seer and now have efficient heating without heat strips down to -5F &lower
    – Ed Beal
    Jul 17, 2022 at 16:46

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