Exploring the Various Types of Indoor Units for Ductless Mini-Split Heat Pumps
HVACR Licensing & Continuing Education
Exploring the Various Types of Indoor Units for Ductless Mini-Split Heat Pumps
by Jonathan Kilburn
Heat pumps have become a popular choice for residential and commercial heating and air conditioning due to their energy efficiency and versatility. Ductless mini-split heat pump systems, in particular, offer flexibility in installation and design, thanks to the wide variety of indoor unit types available. Capable of providing refrigerant to both single-zone or multi-zone head units without the need for an air handler, these systems are gaining popularity with homeowners who need to refrofit adequate systems without requiring a typical central air or heating systems, while also offering energy savings. Each head unit type has unique features, advantages, and ideal use cases, making it important for HVAC technicians to understand their differences. This article will explore the key characteristics of wall-mounted, cassette ceiling-mounted, floor-mounted, free-standing, and through-wall indoor units, providing a detailed analysis of their benefits, drawbacks, and suitable applications.
Will it Work for Everyone?
The only way to know if a mini-split unit is suitable for your specific home depends on several factors. If there is already existing ductwork then a ducted system may be the best heating or cooling solution for indoor air quality. Also knowing what spaces need to be individually conditioned, like basements and bedrooms, will allow an HVAC professional to calculate the BTU (British Thermal Unit) requirements for a ductless mini-split system. This may require a single-zone mini-split or a multi-zone system. Each type of system can provide the necessary outdoor unit to match different types of mini-split head units or indoor units. Energy saving and energy star ratings may or may not be better than a current system. While wall mounted mini split systems can offer a lot of potential energy savings, the cost for replacing a home’s entire boiler or furnace may not return on the investment as much as expected.
There is a difference between concealed duct, ducted, and ductless when referring to HVAC systems. Mini-splits are ductless and transfer heat in the air via refrigerant as opposed to moving conditioned air into a space. Concealed duct and ducted heat the air in a separate area and transfer that air to a space that needs to be conditioned. Here, we will be discussing ductless systems relying heavily of refrigerants as the primary media for heat transfer.
Wall-Mounted Units
Wall-mounted units are among the most commonly used indoor components for mini-split systems, offering a sleek and compact design that makes them suitable for a wide range of spaces. These units are typically installed high on a wall, allowing for efficient air distribution throughout the room in both heat and air conditioner modes.
They are favored for their simplicity and efficiency. Their elevated position helps optimize airflow, making them effective at maintaining consistent temperatures. Installation is straightforward, requiring minimal wall space and avoiding significant structural modifications. Wall-mounted units are also relatively easy to service, with accessible filters that can be cleaned or replaced quickly. They are often operated with remote controls and have an internal thermostat constantly monitoring and adjusting air flow.
In recent years new ‘picture frame’ style wall mount units have become available. They function in a very similar manner to standard wall mounts, but do not have as much air flow due to the lack of front facing vents. Easy to overlook, they can blend in well and perform adequate heating and cooling when placed properly.
However, wall-mounted units may not suit all room designs or aesthetics. While modern models offer stylish options, their visibility can be a drawback in spaces where a more discreet solution is desired any may not be better than a window air conditioning system that can be hidden behind a curtain. Because they are installed higher up, they may not provide optimal comfort in rooms with poor insulation or uneven heat distribution.
These units are ideal for bedrooms, living rooms, and other common spaces where efficient and unobtrusive climate control is needed. They work particularly well in areas with limited floor space or where maintaining an open layout is a priority.
Cassette Ceiling-Mounted Units
Ceiling cassette units are designed to be installed within a ceiling between the joists, with only the grille visible. These units are commonly used in commercial settings or high-end residential spaces, offering a discreet, modern heating and cooling system appearance.
One of the key advantages of ceiling cassette mini-splits is airflow, allowing them to condition larger spaces effectively. This design makes them a popular choice for offices, conference rooms, and open-concept living areas. They are highly discreet, blending seamlessly into the ceiling for a clean and professional look.
The primary drawback of cassette units is their installation complexity. These units often will require a false or suspended ceiling to house the indoor component, which can increase labor costs and limit their use in certain buildings. Plumbing refrigerant and condensation lines for ductless heat pumps provides additional challenges when in a ceiling. Maintenance is also more challenging, as accessing the unit often involves removing ceiling panels or covers directly overhead.
Cassette units are best suited for larger spaces where aesthetic considerations and even air distribution are top priorities. They are an excellent choice for commercial spaces or upscale homes looking for a balance of performance and design.
Floor-Mounted Units
Floor-mounted units sit low on the ground by a wall and are designed to provide efficient heating and cooling at ground level. These units are effective in rooms where wall-mounted or ceiling-mounted options may not be practical or when retrofitting a home with one-pipe steam radiators.
One of the primary benefits of floor-mounted units is their accessibility. Positioned at ground level, they are easy to operate and maintain, making them a user-friendly option for individuals with mobility issues or in homes with small children. These units are also highly effective at heating, as warm air naturally rises, ensuring even distribution from the ground up. When replacing radiator under windows, they mimic the natural drafts from cast iron radiators providing a blanket of warm air over the window. In areas with no wall space, like finished attics or Cape Cod homes with slanted walls, a floor mounted unit may be the only potential solution.
Despite their advantages, floor-mounted units require more floor space than other types, which may be a concern in small or cluttered rooms. Their placement also makes them more susceptible to blockages from furniture or household items, potentially affecting performance.
Floor-mounted units are ideal for older homes with limited wall space, rooms with low ceilings, or areas requiring a strong heating performance. They are also well-suited for bedrooms and living rooms where accessibility and comfort are key considerations.
Free-Standing Units
Free-standing units are large systems that can be placed anywhere in a room, provided they have access to the necessary connections. These units offer maximum flexibility in placement and are often used as a statement piece. They’re essentially an air handler with a fancy shell.
The main advantage of free-standing units is their placement potential. The ability to move high volumes of air in a large space is nothing to overlook. Office building, doctor’s offices, and even large open concept homes may benefit from having a free-standing indoor unit to complete their mini-split air conditioner or heater. Free-standing units also eliminate the need for wall or ceiling modifications, simplifying the installation process.
However, these units typically take up a significant amount of floor space and may not blend seamlessly with a room’s design. Noise levels can also be higher than those of wall-mounted or ceiling-mounted units as the blower motor, vents, and filter are housed in occupied spaces.
Free-standing units are a practical choice for extremely large spaces or where wall installation is restricted due to building requirements or wall materials. They are also useful as supplemental heating or cooling options in areas that require additional temperature control.
Through-Wall Units
Through-wall units are designed to be installed directly into an exterior wall, with the indoor component on one side and the outdoor component on the other. These units provide a permanent and compact solution for heating and cooling. They are not ‘mini-split’ systems as we understand them. They’re basically wall unit air conditioners with a reversing valve.
The primary advantage of through-wall units is their space efficiency. By eliminating the need for extensive ductwork, refrigerant lines, or additional indoor components they offer a streamlined and unobtrusive option for climate control. These units are also highly effective in individual rooms or small spaces, providing targeted heating and cooling. It’s very common to find them in hotel rooms and hospitals that offer residents full control of climate needs.
On the downside, through-wall units require significant structural modification during installation, including cutting into an exterior wall. This can increase costs and limit their appeal for certain building types. Additionally, their fixed position means they lack the flexibility of portable or multi-room systems.
Home and building warranties should be taken unto account when placing these systems. The modifications to a building structure may require additional permitting or oversight. Ancillary rooms or additions, like sunrooms, are a great option to add a through-wall unit during the design phase.
Which Unit is Best for Your Application?
Each type of indoor unit offers distinct advantages, making the choice largely dependent on the specific needs of the space and the preferences of the user.
For general use, wall-mounted units are a practical and efficient choice, offering a balance of performance and accessibility in most residential and light commercial settings. Cassette ceiling-mounted units excel in larger or more open spaces where aesthetics and even air distribution are priorities, while floor-mounted units provide strong heating performance and easy accessibility, particularly in older or unconventional spaces. Free-standing units offer unmatched flexibility for temporary or supplemental climate control needs, and through-wall units provide a compact and efficient solution for single-room applications.
For HVAC technicians, understanding these unit types and their applications is essential to recommending the best solution for clients. A thorough knowledge of each option ensures that technicians can address a variety of needs, from maximizing energy efficiency to achieving specific design goals. By aligning unit selection with the unique demands of each project, technicians can deliver tailored solutions that enhance comfort and satisfaction.