Ductless mini-split vs central ducted heat pump: pros and cons

When it comes to heat pumps for homes, there are two main types to choose from: ductless mini-split systems, and ducted central systems.

Both work on the same basic principles: they use the refrigeration cycle to take heat from the outdoors to warm your home, or move excess heat from inside and dump it outside to cool your home.

Both types have similar advantages: they are highly efficient, with federally-mandated SEER ratings of at least 14 and HSPF ratings of at least 8.8 in 2023 and newer models. Cold climate heat pumps are available in mini-split and central designs too.

But there are differences that make mini-splits and central heat pumps more suited to particular installations. For example, in retrofit installations where a home already has forced air ducts, a central heat pump is often a better choice. But even in that situation, a mini-split system can have some advantages.

Understanding the differences and pros and cons of ductless versus ducted heat pumps can get pretty confusing, so this article will hopefully help to clear things up so that you make a smart decision for your home.

How heat pumps work: a quick overview

Before we get into the details, it’s worth reviewing the basic components that make up a heat pump so that we can understand the differences between mini-split and central designs.

As mentioned in the introduction, a heat pump is based on the refrigeration cycle. This is the same process used in refrigerators, air conditioners, and dehumidifiers. You can read my primer on heat pumps for a more in-depth description, but the refrigeration cycle works by the phase change of a refrigerant. The refrigerant is pumped through a closed copper loop where it is alternately compressed from a gas to a liquid – releasing heat – and then passed through an expansion valve that allows the liquid refrigerant to expand back into a gas, causing it to absorb heat and cool down.

The indoor and outdoor heat exchangers of a heat pump allow the refrigerant to either absorb heat from the outdoors or release heat to the outdoors, depending on which mode the system is operating in.

This basic design is the same for both mini-splits and ducted units. Where they mainly differ is how the indoor components function.

Central ducted heat pumps: a basic explanation

For consumers who are new to heat pumps, one of the more confusing things is the name given to central ducted heat pumps. You might see them referred to as centrally ducted heat pumps, ducted heat pumps, central heat pumps, or split-system ducted heat pumps. All of these labels refer to the same system design.

This type of system provides the heating and cooling for a central forced air system, which uses ducts and vents to supply conditioned air throughout a home. A central heat pump is installed in a similar fashion as a central air conditioning system, so if you have an older central A/C that needs replacing, switching to a central heat pump would be a relatively easy upgrade. (In fact, this is what I did in my own home.)

Another potential point of confusion is that because mini-split systems include the word split in the name, you might think that central systems are not split. In fact, they’re split systems too, because the components of the system are split into outdoor and indoor units.

There is an outdoor unit that contains a heat exchanger and compressor, and an indoor unit which also contains a heat exchanger. The indoor unit, which is called a cased coil, fits into the duct system. The cased coil can be mounted into the supply or return side of the duct system. If you already have a forced air system, the existing air handler (ie. the blower motor and fan) may be compatible with the heat pump. However, if you have a single speed blower motor and your heat pump is designed to paired with a variable speed motor, you will need to upgrade the blower too.

Mini-split heat pumps: basic design

The other popular type of heat pump is a ductless mini-split. As the name indicates, these don’t rely on ducts. Instead, they supply refrigerant – which will be either hot or cold, depending on the mode the heat pump is operating in – directly to an indoor unit, which is also called a head unit. The head unit includes a heat exchanger and fan, and supplies conditioned air directly into a room. In other words, the components that you would find in a cased coil and air handler of a forced air system are scaled down into the head unit of a mini-split system. That’s why it’s called “mini”!

The most common head units are mounted high on a wall. You can see an example on the right wall in this picture:

Unlike a forced air system which can distribute conditioned air into vents throughout a house, a mini-split system only delivers heating and cooling to rooms with a head unit. Mini-split systems will have one or more head units that are paired with an outdoor unit.

Outdoor units for mini-split systems tend to have smaller capacities and have a characteristic slim design that looks like this:

One of the advantages of mini-split systems in their flexibility. There are very small systems that have only one indoor unit, which might be used to replace an old window air conditioner. But mini-splits can also have multiple zones - 6 or even more - to supply conditioned air for a large home. For large systems, multiple outdoor units might be needed.

Refrigerant is supplied to the head units pipes that might be 5/8" or narrower. That’s a much smaller volume than an air duct, so mini-splits require very little interior wall space compared to the supply and return ducts of a forced air system. That makes for a lower cost installation due to both materials and labor. It also makes it possible to retrofit a heat pump into an older building that doesn’t already have ducts (such as a home that is heated by hot water radiators).

A quick note about packaged units

Both mini-split and central ducted heat pumps are split systems, but if you’re doing some research you might also come across packaged heat pump systems. Packaged systems are not split: all of the components are contained in a single unit that is installed outdoors. That includes the blower motor, which means that a packaged unit outputs conditioned air into the building. To install a packaged heat pump in a building, there will need to be ducts that terminate at an exterior wall near the heat pump.

Packaged systems are popular for commercial buildings and are not very commonly used for homes.

The advantage of packaged systems is that they’re easier (and therefore cheaper) to install because all of the components are contained in a single unit. The downside is lower efficiency compared to central and mini-split systems. This lower efficiency is the result of the blower motor being outside. Packaged systems also require a large penetration in an exterior wall for ducts, which compromises the insulation of the wall at that point.

Despite that, you might occasionally find residential settings where a packaged system is more cost effective than other heat pump types.

Advantages of central ducted heat pumps

Now that you know the differences between mini-split and central heat pumps, we can learn about the pros and cons of each design.

Here’s a summary of the pros and cons of central ducted heat pumps:

Central heat pumps work well if you already have ducts

This website is focused on home electrification and switching away from natural gas, so there’s a pretty good chance you’re reading this article because you have a forced air gas furnace that you’re thinking of upgrading.

Or maybe you have an aging central air conditioner that you want to upgrade. That was my situation: I had a 25 year old central air conditioner that wasn’t very efficient and used R-22 refrigerant, which is now banned under the Montreal Protocol¹ due to its impact on ozone depletion.

If you’re in this situation, adding a central heat pump is essentially a drop-in replacement for your central air unit. Your central air conditioner will already have a heat exchanger in either the supply or return side of the ducts; the new heat exchanger for the heat pump will replace this.

If you don’t have central air already, the installer will need to cut into either the return or supply ducts and insert the heat exchanger. You will likely be able to use the same blower motor for your furnace, unless you choose a heat pump that requires a variable speed blower motor.

The advantage of this is that you can reuse your existing infrastructure. It’ll be cheaper than installing a mini-split system because the delivery system (ie. your vents and ducts) is already installed.

Another advantage is that you can retain your existing furnace as fallback heat when the outdoor temperature is too cold for the heat pump to operate effectively. Often heat pumps will have the option to use electric resistance heating – sometimes called electric strip heating – as backup heating, but if you have an existing furnace, the system can be programmed to fire up the furnace below a certain temperature. This is something I can configure with my Ecobee smart thermostat.

This can be a good option if you have an older furnace that is still in good operating condition. If you don’t live in a very cold climate or you opted for a cold climate heat pump, the furnace might be used only a couple days a year.

Forced air systems will often have better air distribution that a mini-split system

In general, forced air systems will have supply and return ducts in every main room of your home. As long as the system is designed well, this means that you’ll have good air distribution to all the rooms of your home.

In comparison, ductless mini-split systems rely on head units to supply conditioned air to selected rooms in your home. Installing head units comes with a cost and outdoor units have a limit on the number of heads they can be connected to, so an average sized home might have only 3 or 4 head units. That’s far fewer than the number of vents in a typical forced air system.

This can be a disadvantage, but it depends on the level of insulation and air sealing in your home. In a very well insulated home, a small number of head units can be sufficient because the home won’t develop cold or hot spots easily. However, in a poorly insulated house, you might find that the smaller distribution system of a mini-split system results in rooms that aren’t heated or cooled very well.

Another feature that forced air systems have is the ability to run in fan-only mode. This turns on the blower motor without any heating or cooling, and can be used to help even out temperature differences in your home or take advantage of air filtration. This is also advantageous if you have a central air filter and want to keep your air clean at all times.

You can integrate air filters, humidifiers, dehumidifiers, and fresh air ventilation into the system

This website is focused on home electrification, and one of the big reasons that homeowners want to switch away from using natural gas is to improve indoor air quality. While gas stoves are a major culprit of poor indoor air, other gas appliances, including furnaces and hot water tanks pose air quality risks too because of leaks and backdrafting.

If this is a concern for you, being able to integrate systems that improve the air quality throughout your home is something that probably interests you.

If you have a forced air system, you’ll have the option to install add-ons such as air purification, humidification and dehumidification, and energy recovery ventilation systems. These systems attach to the ductwork and make it easy to improve the quality of your conditioned air. Energy recovery or heat recovery ventilation systems pull in outside air and push out stale indoor air, but pass the two air streams through a heat exchanger, allowing the indoor air to warm up the outdoor air (or cool it down in summer), saving you energy compared to simply opening a window.

Head units for mini-split system often do have air filters, but they’re mostly intended to protect the components of the unit rather than clean the air. In contrast, air filters added onto forced air systems can filter to HEPA standards or even incorporate sanitizing UV light.

If you want that type of air filtration, humidification or dehumidification in a home with a mini-split system, you’ll need to use standalone units instead - and they won’t cover your whole home.

Central heat pumps avoid the need for visible indoor units

The room vents for central heat pumps are a lot more discreet than the indoor units needed by mini-splits. The most common type of heat unit for mini-splits are wall-mounted units. While they are mounted high on a wall, they can be quite bulky and noticeable, especially if your wall isn’t white (as these units usually are).

Mini-split head units do come in different configurations, including floor mounted units that look more like traditional radiators and ceiling cassettes units that are flush with a ceiling. However, ceiling cassettes aren’t an option for every location. For example, all mini-split head units require a drain pipe to carry away water condensation when the system is operating in cooling mode.

Because of these limitations, mini-splits can make for a less aesthetically-pleasing installation compared to a central unit.

Advantages of mini-split heat pumps

While central heat pumps tend to be the first choice when upgrading an existing forced air system, mini-split heat pumps are often a better alternative for newly built homes and some retrofit situations.

Here’s an overview of their pros and cons:

Good choice for when you want to do smaller retrofits

Sometimes you might want to add supplemental air conditioning or heating to only part of a home. For example, maybe you’ve got an old window air conditioner or two that need replacing, or you have a basement that can never get warm in the winter.

Mini-splits are a great choice in these situations because you can keep your existing heating or cooling system and add just one or two head units to the areas of your home that you want to make more comfortable. This can be lower cost that upgrading your entire heating and cooling system, and is less unsightly than having an air conditioner hanging out your window.

Often the only practical upgrade option for old homes

If you have an older or historic home with plaster walls and radiators, it may be impractical or very expensive to rip out walls to install the duct work needed for a central heat pump.

Ripping into plaster and lathe walls is an expensive proposition. Older homes might also have historic wood trim that might need to be removed for an upgrade. Exterior walls might also be poorly insulated, which would steal energy from ducts that are located in those walls.

You might also want to add air conditioning to an older home, but want to keep the existing heating system, which might often use hot water or steam radiators. While air-to-water heat pumps – known as hydronic heat pumps – can be used to supply hot water, the existing distribution system for hot water radiators in an old home may be be suitably designed for a heat pump system that delivers lower water temperatures.² Mini-splits would let you continue to your existing central heating system, but add air conditioning as well as supplemental heating in the rooms that need it.

Mini-splits let you control zone temperatures individually

One big advantage of mini-split systems is that you can set the temperature of the head units individually. This means that you can make different areas of your home warmer or cooler, or turn off units in areas that are unoccupied, saving you money. With most systems, you can control the head units with a remote control.

Some forced air systems are designed to let you have individual control over different areas – known as zones – in your home. However, they are often only dual zoned, such as for a first and second floor. In contrast, larger mini-split systems might have 6 or more head units. This means that you can have a greater degree of control with mini-splits than with zoned forced air.

While it’s also true that with a forced air system you can manually open and close vents in rooms, this can reduce the efficiency of the system because the reduced airflow can add back pressure on the blower motor, causing it to work harder and consume more electricity. Many forced air systems already have poorly designed duct systems³, so closing vents can exacerbate this problem.

Head units come in a range of design options

One of the potential disadvantages of mini-split systems is that instead of hiding the mechanical components in a basement or utility closet and walls, the indoor units are mounted in your living areas, which can be obtrusive.

Fortunately, there are alternatives. Some manufacturers offer floor-mounted units that look like traditional radiators, or ceiling cassettes that fit between standard joists and have vents that are flush to the surface of the ceiling.

Not every HVAC installer will recommend these alternative indoor units, and they may not be suitable in every location in your home. In any case, manufacturers do offer alternatives for homeowners that don’t like the design of the more common wall-mounted head units.

Mini-splits offer the highest efficiency

If your goal is maximum energy efficiency, mini-splits are your best option. All other things being equal, mini-splits will deliver more heating and cooling energy into your living spaces than a central ducted system.

This is because ducts can waste up to 20 to 30 percent of the energy that enters the system instead of delivering it into your living spaces⁴.

Leaky ducts are a common problem in many homes with forced air systems. Holes, poorly fitted connections, and seams that aren’t sealed are the cause of many leaks. In addition, metal ducts that aren’t insulated can radiate energy into unconditioned spaces, such as walls and basements. Finally, many duct systems are undersized, putting back pressure on the blower motor, wasting energy and causing poor airflow to rooms at the end of the duct run.

Energy loss isn’t the only issue. Leaks on the return side of the system can suck in pollution, such as dust or even radon or carbon monoxide from a basement, and distribute it throughout your home.

Mini-splits avoid this problem by delivering refrigerant directly to head units in your living spaces using insulated pipes. This means that much less of the heating or cooling energy generated by the outdoor compressor will be wasted. It also means that you don’t have to worry about leaky ducts potentially blowing pollutants around your home. (The flip side of this is that – as mentioned earlier – forced air systems can integrate HEPA-level filtration. However, even HEPA filters can’t filter out dangerous gases like radon.)

Bottom line: central and mini-splits offer two great heat pump options

Whether you’re switching from gas to electric or upgrading from inefficient electric baseboards or an electric furnace, there’s probably a heat pump option that would work well for your home.

Central and mini-split heat pumps work on similar principles, but use different methods to deliver heating and cooling into your living areas. Much of the difference boils down to forced air versus ductless head units, so whether you’re upgrading an existing system or designing a brand new one will largely dictate your choice. Before talking to an installer, make sure that you understand the pros and cons of both types of systems so that you can make a good choice for your home. As always, you should also get quotes from multiple HVAC companies.

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