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Everything You Need to Know about Ductless HVAC Systems

Published on: November 22, 2013

Providing heating and air conditioning to a home or commercial facility can be difficult if the structure has limited space or several different areas that require variable levels of heating and cooling. If your new construction or renovation project is presenting this type of challenge, consider the merits of installing a ductless heat pump. Ductless systems, also called mini splits, provide the full heating and cooling capacity of a traditional heat pump with benefits in performance and flexibility that a regular heat pump can’t match. Here is a brief guide to ductless systems that will help you understand how these types of HVAC equipment work and what they can offer you in terms of comfort, efficiency, economy and convenience.

The Basics of Ductless Systems

Though ductless systems are configured differently than standard heat pumps, they offer the same powerful and efficient performance provided by any full-size ducted system. A ductless system consists of two sets of components, one installed outside and the other inside your home or business. The outdoor components include a cabinet and the main system equipment, such as the condenser, compressor and evaporator. This cabinet takes up about as much space as the outdoor cabinet of a standard heat pump.

The components include four to eight smaller air-handling units that distribute the heated and cooled air produced by the system. This is what gives the ductless system its name; indoor comfort is controlled by these air handlers, meaning that no ductwork is required for distributing conditioned air. The indoor units are connected to the outside unit by cables, refrigerant lines and drainage pipes routed through a conduit in the wall. This conduit requires a relatively small hole in the wall of 3 inches in diameter or less.

The Function of Ductless Systems

Ductless heat pumps work on the same principle as full-sized models. They capture heat and move it from place to place, depending on whether conditions call for indoor heating or cooling. In the summer, the equipment absorbs heat from inside your home or commercial facility and releases it outdoors. In the winter, the system pulls heat from even cold winter air and brings it indoors.

A liquid refrigerant circulates in a set of pipes connecting the indoor and outdoor components of the ductless system. Heat capture and release is accomplished when the refrigerant changes from a liquid to a gas and back again. When the refrigerant evaporates into a gaseous form, it absorbs heat. The hot gas circulates through the pipes and returns to liquid form in the condenser. During this change of state, heat is released. Once the refrigerant has returned to its liquid state, the cycle of evaporation and condensation begins again.

The indoor air handling units distribute heated or cooled air to your indoor spaces, depending on whether heat has been removed from or brought into your home. Each indoor unit has its own thermostat that allows the unit to provide variable levels of heating or cooling based on the needs of the occupants of the area.

The Advantages and Disadvantages of Ductless Systems

You can count on a ductless mini split system to provide the same level of comfort as a larger heat pump. However, the ductless systems offer a range of advantages that full-sized heat pumps cannot match. These advantages are what make a ductless system the better choice in many circumstances.

  • High efficiency: Ductless systems are as energy efficient as their larger ducted counterparts. In many cases, they perform even better than full-sized heat pumps since there is no ductwork where air and energy loss can occur. For example, ductless mini-split heat pumps must carry a Seasonal Energy Efficiency Ratio (SEER) of at least 13, which is the same as that for a central air conditioner. The higher the SEER number, the more efficient the unit will be.
  • Better monthly savings: The high efficiency of a ductless mini split means it will provide significant monthly savings over standard furnaces and air conditioners. Ductless systems typically decrease monthly heating and cooling costs by 30 percent or more.
  • Easier installation: Ductless systems are easier to install than standard ducted systems. Since they require no ducts, no consideration has to be given to planning and installing a duct network and there is no need to provide space for these bulky air distribution pipes. The indoor air handling units are small enough to place almost anywhere you want them: mounted on the wall, suspended from the ceiling or tucked away out of sight. Most often, indoor units are attached to a wall near the ceiling. Wall units typically resemble small fans or rectangular radiators, while floor units look like square radiators.
  • Increased zoning options: The independent operation of the indoor units offers increased opportunities for creating zoned heating and cooling. One or more units can be installed in a space that requires additional conditioning, or you can choose to not put an indoor unit in areas that need no heating or cooling at all. Occupants of your home or commercial space can maintain their individual levels of comfort without interfering with the heating and cooling in adjoining rooms.
  • More interior design options: The ability to place the indoor units where you want them improves the design and arrangement options for your living spaces. The units can be incorporated into the design or simply placed in an inconspicuous area where they will be out of sight.
  • Quiet operation: The indoor air handling units operate very quietly as they distribute air. The majority of the system’s noisy components are housed in the outdoor cabinet where they will not interfere with indoor noise levels.

The biggest disadvantage to a ductless mini split system is greater expense. Ductless systems are usually more expensive than standard heat pumps or other heating and cooling systems. However, their improved flexibility and high efficiency usually offsets the cost disadvantage. Like most heat pumps, a ductless system provides enough monthly savings to allow the owner to recover the cost in ongoing savings alone by about the mid-point of the equipment’s expected life span.

Choosing Ductless Systems: Sizing

A ductless system must be properly sized for the space it will heat or cool. That is, it must have enough functional capacity to provide enough conditioning to meet the requirements of the space. It can’t be too small or the heating and cooling will be inadequate. The system will also work too hard and cost more to operate. It can’t be too large or it will waste energy and money.

Consult with your trusted local HVAC contractor for help with sizing your ductless equipment. The best option is usually to have your HVAC pro conduct a load calculation on your structure. This assessment will determine the heating and cooling load, which is the amount of heating and cooling required to keep the interior spaces at the temperatures you prefer. The load calculation requires a careful inspection of the structure and will take into consideration factors such as local weather and climate, thermal and structural characteristics of the building and overall indoor temperature needs.

Load calculations should be performed using industry-standard resources such as Manual J, “Residential Load Calculation,” published by the Air Conditioning Contractors of America.

Maintenance for Ductless Systems

Keeping your ductless system operating smoothly and efficiently requires regular preventive maintenance. Like any other HVAC system, if your mini split is neglected, performance will decrease, efficiency will drop and malfunctions and breakdowns become more likely.

Maintenance on a ductless mini split system should be performed by an HVAC professional at least annually. A better option for ductless systems is to have maintenance performed twice a year, once before heating season and again before cooling season. Some of the more important maintenance tasks include:

  • Air filter changes: Air filters capture and remove particulates from the air flowing through the system. When they get dirty, they can interfere with airflow and cause the system to malfunction. Check filters at least once a month and change them if they are dirty. If your indoor air is generally clean, you may be able to get by with changing filters every three months.
  • Clean the outdoor unit: Keep grass, leaves, sticks, mud and other debris from collecting in and around the outdoor unit. This material can interfere with necessary airflow and decrease heat transfer and overall system function. Trim vegetation to allow at least two feet of clearance on all sides of the outdoor unit and five feet of open space above it.
  • Check refrigerant levels: Ductless systems are usually charged, or filled with, refrigerant at the factory, but use and small leaks can decrease the refrigerant level. The system must be kept charged at factory-specified levels to work properly. If refrigerant levels are dropping, check the system for leaks or refrigerant theft. Install locks if necessary to deter theft.

Your local HVAC professional can provide all the information and services you need to install a ductless mini-split system in your home. Contact us today for help finding HVAC specialists who can help you decide if ductless systems are the best choice for your home heating and cooling needs.