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This is a very ignorant question, I know, but after reading several mini-split product descriptions I'm still confused.

I already have an adequate heating system.

I need air conditioning and central air is too expensive. Unfortunately my window unit is so loud I can't hear my computer, phone, or knocks on my door. So, I'm thinking that a mini-split sounds like the best solution (hopefully these things are quiet, right?).

However, I'm unclear on if I need the piece that goes outside. My understanding is that that's the "heat pump". Intuitively it seems like I would have to have a piece that goes outside, but the name throws me off because I don't need heat and if I don't have to have it then I don't want it because I need to minimize cost.

I'm not sure if the refrigerant is in that part or not?...

enter image description here

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    How are you going to pump heat out of the house without a heat pump?
    – David Schwartz
    Jun 6, 2016 at 3:47
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    It helps to realize that in physics, there's just heat and the lack of heat. That's part of what makes cooling so hard: you cannot "make cold" or "unmake heat". To cool a room, you have to remove the heat in it. And usually that involves removing the heat to an even hotter environment (outside).
    – MSalters
    Jun 6, 2016 at 9:00
  • Not necessarily: there are "single block" units that requires two holes in the wall and both the evaporator and the condenser are inside, these are usually noisier and more expensive than split system but are a great deal for those who can't put the outdoor unit on. These looks like a fan-coil but are capable to cool (and some models also to heat). An example is Olimpia Splendid unico air 8 hp
    – DDS
    Jan 8, 2021 at 8:42

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Yes. you need both pieces. An air conditioner is a heat pump that moves heat from inside to outside. A dual mode system that can supply heat just runs the same process "in reverse."

A heat pump draws heat from some source (often air) and transfers it into your house. An air conditioner is the same thing, but instead of drawing "free" heat from some thermal source, it draws heat from inside, and transfers it outside.

Your window A/C unit simply incorporates all of these pieces into one box, which necessarily hangs in your window so that they evaporator coil can be inside and the condenser coil outside. A "mini-split" system just separates these two, and is just an alternate installation style of what is commonly referred to as central air. The only difference is that instead of integrating into built-in ductwork (which might not be there), it instead hangs a unit on your wall. That unit incorporates the evaporator coil and fan, much like the inside half of your window AC. You still need the other half as well.

The image below is from Wikipedia

heat pump diagram

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  • Thanks. Do you know if I have to drill a hole through the wall in every room to do this? That's what they did on "This Old House" when they installed one in a garage. Seems like a drastic thing to do to my walls...
    – Hack-R
    Jun 5, 2016 at 23:18
  • You just need to run the lines that connect the two units. If the inside unit can be located on (the inside of) an exterior wall opposite where the condenser will be located, it will be a very simple path between the two. But they will also need to run power to both.
    – Tim B
    Jun 5, 2016 at 23:23
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    @Hack-R "in every room"...just how many of these things are you installing? At some point, it becomes much cheaper to get real central air - a single larger unit is probably going to be more energy efficient than a bunch of smaller ones.
    – Grant
    Jun 6, 2016 at 1:15
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    Single larger unit more efficient? Maybe, if you are trying to cool the whole house to the same temperature. However, by zoning and controlling areas separately at different temperatures the mini-splits become more efficient.
    – ArchonOSX
    Jun 6, 2016 at 2:01
  • @Grant Well I figured I would at least get a quad zone. That would hit the master bedroom, living room, and one for each of the 2 upstairs bedrooms. That would leave the dining room, kitchen, and sun rooms without A/C but I figured I could put a window unit in the sun room (since the noise wouldn't matter as much there) and I guess I'd move all my fans to the dining room and kitchen area. Thing is I don't have ducts so central A/C with ventilation + installation would be at least $7,500. Not that I wouldn't prefer central, I just have to save $ and idk if this old house could support ducts.
    – Hack-R
    Jun 6, 2016 at 2:17

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