Ductless mini-splits

A mini-split is a split system in a smaller form. Some ductless air conditioners and heat pumps are built as split systems and are commonly called mini-splits or multi-splits. The outdoor unit is mounted on an outside wall or on a pad, and refrigerant tubing and control wiring connect it to the indoor unit through a small hole in the wall. Refrigerant carries the heat straight to the indoor heads, which deliver heated air to the room.

Leaving out the ducts changes how the system behaves. Ductless heat pumps save energy by avoiding ducts, or by using much more compact duct layouts inside the living space. In general, ductless systems tend to be more efficient, remove less moisture when cooling and filter the air less. That trade is worth knowing before you choose one.

Source: U.S. Department of Energy · ENERGY STAR

Ducts are the first thing to think about. They are a popular choice for adding to or replacing heating and cooling in a home without ducts, such as one heated by baseboard or wall electric heaters. They are an alternative to radiator or baseboard heating and a replacement for window units for cooling. They are also an excellent choice when rooms are added, or when an attic, basement or garage becomes living space.

Indoor units come as high wall units, ceiling cassettes and floor consoles. Indoor units mounted near the ceiling draw in warmer air from the room, which helps in cooling but costs efficiency in heating. Many ductless heat pumps sense the room's temperature at the indoor unit's intake, so a high wall unit or ceiling cassette reads the temperature near the top of the wall or the ceiling. Keep that in mind if the room feels different from the setting where you sit.

Source: U.S. Department of Energy · ENERGY STAR

Not every mini-split is built for a Chicago winter. Many newer ENERGY STAR certified mini-splits heat well even in the coldest climates, using advanced compressors and refrigerants that improve low-temperature performance. A newer class of inverter-driven ductless heat pumps can heat a home comfortably at outdoor temperatures as low as -15°F. Less expensive models not built for cold may work well above freezing, but they lose capacity and need other heat when it gets cold.

Size matters as much as the model. Working out how much heating and cooling the space needs is essential to keeping cost down and getting good performance, comfort and life from a ductless system. Quality installation is arguably more important than the make and model for performance, efficiency and how long the system lasts. In Chicago, installing a new heat pump or air conditioning system for a single home is eligible for the Express Permit Program, based on proper load calculations.

Source: ENERGY STAR · Northwest Energy Efficiency Alliance · U.S. Department of Energy · City of Chicago

Indoor units need more regular attention than many owners expect. Many ductless systems have washable mesh filters that catch fine particles poorly but keep airflow open. A typical maker's recommendation is to clean these mesh filters every two weeks, by washing or vacuuming. Heat pump filters should be cleaned when they look dirty or when the filter light comes on.

Dust that gets past the filter builds up inside. Because filtration is often poor, more dust gathers on the indoor unit's inner parts, which can quickly reduce performance, efficiency and indoor air quality. Most wall-mounted units are built in a way that lets moisture collect on the blower wheel during cooling, so more dust sticks to it. Dust and moisture together can lead to mold growth, and this is more common in high wall units than in ceiling cassettes and floor consoles.

You can look for the warning sign yourself. If you see dust and mold built up on the blower wheel and the air vanes, it is time for a deep cleaning. Deep cleaning is generally not a do-it-yourself job, because indoor units are hard to take apart and the work needs special sprayers, covers and cleaning agents.

Source: U.S. Department of Energy · ENERGY STAR

Where the outdoor unit sits makes a big difference in a Chicago winter. Install outdoor units well above snow height, on stands or wall mounts, and be aware that a unit fixed to a wall can cause vibration problems. On the ground, the soil should drain well and support the pad, and snow legs should be tall enough for the snow your area gets. Do not put outdoor units where water or melting snow or ice will fall on them, or protect them with a cover if they are there.

Winter running brings water with it. Outdoor units release water when they defrost in winter, and that water can form icy patches. If the outdoor unit has a drain pan heater, it should only run as part of the defrost cycle. Installation manual clearances are minimums and are often not enough room for maintenance, cleaning and clearing debris.

Your part is simple. Keep indoor and outdoor units clean and clear of dust, snow, leaves and other debris. After a heavy snow, check that the outdoor unit is not buried and that the area around it is clear.

Source: U.S. Department of Energy · Northwest Energy Efficiency Alliance · ENERGY STAR