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Mini-Split Air Conditioner Buying Guide

Britney, 11/11/2016

BUYING A NEW MINI-SPLIT AIR CONDITIONER?

Mini-split air conditioners are a compact and efficient solution for providing cooling and often heating to your home. Used throughout Europe and Japan for decades, these systems are gaining popularity in the U.S. for their quiet operation and versatile applications.

WHAT ARE MINI-SPLITS?

HOW MINI-SPLIT SYSTEMS WORK

As with Central air systems, mini-split systems are “split” into a two component types: an outdoor compressor which pumps a pressurized air refrigerant, and an indoor evaporator which circulates the refrigerant, extracting heat from the indoor space to provide cooling.

Some systems also have a heat pump, which provides heat by extracting heat from the outside air to warm the air inside. A mini-split system can consist of up to four and even eight indoor units to cool and/or heat multiple zones at a time.

Mini-split systems rely solely on small tubes of refrigerant that run between the outdoor and indoor units, unlike a central air system, which requires ductwork to distribute the air from the condenser to the indoor unit(s).

THE MINI-SPLIT ADVANTAGE

HEATING AND COOLING OPTIONS

Unlike most Window AC units, mini-split models can provide not only cooling, but heating as well. This can be a versatile option for heating on a room-by-room basis, or it can be used home-wide as an energy-efficient alternative to a traditional heating system.

ENERGY EFFICIENCY

Unlike most Window AC units, mini-split models can provide not only cooling, but heating as well. This can be a versatile option for heating on a room-by-room basis, or it can be used home-wide as an energy-efficient alternative to a traditional heating system.

Reduced Energy Loss

Ductwork leakage can often account for up to 30% energy loss. As they are generally ductless, mini-split systems greatly reduce and sometimes even eliminate this inefficiency.

Energy-Saving Technology

Most mini-split systems include responsive technology to provide energy efficiency that other AC systems cannot. Window units and central air systems are most often limited to only two settings – “Off” or “On.” This can contribute to excessively hot or cool environments. In contrast, the inverter compressor technology in mini-split systems enables the compressor to adjust its motor speed based on higher or lower energy demand. This variable usage both conserves energy over time and eliminates the energy lost during a traditional AC system’s startup.

Heat Pump vs. Electric Heating

When a mini-split system operates in heating mode, it’s using electricity to simply move heat rather than create heat. As a result, mini-splits use significantly less energy than electric heaters and other traditional systems.

ROOM-BY-ROOM TEMPERATURE CONTROL

With central air, there is one central thermostat that controls the temperature for all connected spaces. This can be less than ideal when some rooms heat up far more quickly than others, as the temperature in some rooms can be uneven. With mini-split systems, you can control every connected indoor unit with a separate thermostat for optimal comfort in any given spot in your home. If you don’t need air conditioning in a room, you can leave it off and save on your energy bill.

QUIET OPERATION

Mini-split systems are the AC industry standard for quiet operation. Indoor unit operating sound levels can go down to as low as 19 dB – quieter than a whisper. Outdoor operating unit levels are much quieter than their central air counterparts, and these units can be installed discreetly without disrupting the surrounding environment.

HEALTHIER AIR

Air filters are a standard feature across most mini-split brands. As air circulates through the indoor units, these filters remove the allergens, dust, mold, and bacteria that often settles on the ductwork of traditional systems, leaving your environment fresher and healthier. Most of these filters are also washable for easy upkeep.

FLEXIBLE INSTALLATION OPTIONS

Mini-split indoor units come in a variety of shapes and sizes to best complement your space. From streamlined wall-mounted units, to barely-there ceiling cassette and concealed duct units, mini-split systems are designed to marry form and function.

ARE DUCTLESS MINI-SPLITS FOR YOU?

CHOOSING THE RIGHT MINI-SPLIT SYSTEM FOR YOUR HOME

Mini-splits have a number of applications for supplemental air conditioning or in place of traditional cooling and heating systems.

Below is a list of common mini-split applications:

  • Homes heated with oil, propane or electric baseboard
  • Homes with heating or cooling systems over 20 years old
  • Homes in which some rooms are used far more often than others
  • Spaces in which indoor AC units are currently used
  • Extensions and home additions

Overview

There are six main factors to consider when selecting a mini-split system.

Rooms and Sizing

A major important factor in choosing your mini-split system is the amount and total size of the rooms you’ll need to cool and/or heat. You will need a good estimate of both the number of rooms and each room’s cooling needs in advance; as mini-split systems are configured with varying heating and cooling capabilities. Under or over-estimating the amount of cooling power needed is a common pitfall that can easily be avoided with the proper understanding of what “zones” and “BTUs” mean.

Zones

For mini-split systems, a zone refers to the entire area that one indoor unit is intended to cool/heat. In most cases a zone will be equivalent to the room in which the indoor unit is installed (although there are some cases where one indoor unit is intended to heat both a main room and a smaller, attached room such as a bathroom). Single-zone systems contain 1 outdoor unit and 1 indoor unit, and are designed for one room, while multi-zone systems are any mini-split systems designed to cool/heat two or more rooms. For multi-zone systems, multiple indoor units are powered by the same outdoor unit.

BTUs

For all air conditioning systems, cooling and heating power is measured in BTUs (British Thermal Units) per hour. A BTU is defined as the amount of heat energy necessary to raise the temperature of 1 pound of water by 1 °F.

The larger your room, the more BTUs you’ll need to heat it, and the greater the BTU capacity your indoor unit will need. In general, a 9000 (9K) BTU indoor unit – the most common indoor unit BTU “class,” or capacity classification – can cool an approximately 20 x 20 ft. (445 sq. ft.) room. An 18K class BTU unit can cool a 1,110 sq. ft. (a 33 x 33 ft.) room.

In many cases, BTU class is a generalization. Actual cooling capacity and heating capacity may be slightly higher or lower than a unit’s BTU class. Both are always listed with a unit’s specifications under capacity. When making a unit selection based on your BTU capacity requirements, keep in mind that mini-split units typically have a slightly higher heating capacity than cooling capacity.

In addition to room size, there are a couple of additional factors that will affect your required BTU.

Sunlight

If the room/space is heavily shaded, you can reduce your required cooling BTU by 10%. If your room gets lots of sunlight, increase your required BTU by 10%.

Average Occupancy

If the room/space is regularly occupied by more than two people, add 600 BTUs for additional person.

Age of Your Home

If your home is drafty or poorly insulated, it will take more BTUs to cool or heat. Increase your estimated BTU requirement by 30%.

Room Function

If the room is a kitchen, add 4,000 BTUs to your estimated total required BTUs.

Like indoor units, outdoor units also have a BTU rating. The most common BTU classes for multi-zone outdoor units are 18K, 24K, 36K, and sometimes even 54K. The sum of indoor BTU capacities may legitimately exceed the listed outdoor unit capacity by 30%. For example, you could purchase a system comprised of one outdoor 36K BTU unit and four 12K indoor units (totaling 48K BTU), that will function effectively in your home. This is because multi-zone systems can operate with each unit under maximum capacity, adjusting with the other unit’s energy requirements.

All of our systems come prepackaged, eliminating all the guesswork as to which configurations are viable. Simply filter our selection by number of rooms, then filter by BTU configuration per room to find the systems that best fit your BTU requirements.

PLACEMENT TYPE

Mini-split systems offer a wealth of placement and installation options, each with its own set of advantages and applications. You can mix and match placement types to suit your custom needs.

Wall Mounted Units

Wall mounted units are the most popular type of indoor unit available and come in the widest variety of sizes, energy efficiency ratings, and BTU configurations. They are also the simplest to install and typically the least expensive. They range in size from roughly 30” – 44” wide, 12” – 14” tall, and 6” – 10” deep, and range from as low as 6,000 BTU to 36,000 BTU in configuration.

Usually installed near the ceiling of an exterior wall (a wall that directly separates the outdoors from indoors), these units require a 3” drilling through the wall to connect the refrigerant lines, drain tube, and connecting wire. The unit must level against a straight, un-slanted wall. If your walls are extremely narrow, have high windows, or the walls are otherwise blocked with furniture or other obstacles, an alternate placement type may be required.

Ceiling Cassette Units

Ceiling Cassette units are installed in the ceiling, recessed behind a decorative grill (required, generally sold separately) that lies flush with the ceiling. These units offer a sleek and unobtrusive look. The BTU configuration of ceiling cassette units typically ranges from 9,000 BTU to 48,000 BTU.

These units are ideal for installation in a T-Bar or other commercial ceiling; however they may also be installed in a traditional joust ceiling if there is enough space between the jousts and vertically above the visible ceiling. These units require a clearance of 10”-14” between the visible ceiling and the surface above. Ceiling Cassette units often come with a built-in drain pump to simplify the removal of condensation from the unit.

Concealed Duct Units

Concealed duct units are actually a hybrid between central air systems and mini-split systems. Unlike the ductless wall-mount and ceiling cassette units, this unit type employs ductwork. These units are typically installed in a dropped ceiling, an attic, a crawlspace or a closet. Ductwork is then installed to carry the air to the intended zone through a grille installed in the wall. The grill is the only visible element of the system and can be customized to match the look of the surrounding area.

In addition to their discreet appearance, another advantage of these units is their ability to supply two neighboring rooms with one unit by branching the ductwork. Note that the temperature of these two rooms would be controlled by only one thermostat.

Keep in mind that as concealed duct units do employ ductwork, they are slightly less energy efficient than ductless placement types. However, for their virtual seamlessness, concealed duct units may prove an ideal application for your space. If you plan to situate the unit a significant length from the blower, check the unit’s specifications to make sure your required duct run (the length of the ductwork) is supported by that blower. A greater distance will require a higher power blower.

LG Art Cool Units

A stylish alternative to the traditional wall-mounted indoor units are units designed to mount as wall art by framing any 20” x 20” photograph or painting. Conditioned air flows out from 3 sides of the unit to cool or heat the room. At under 5 inches thick, this unit type is a stylish and unobtrusive AC option. These units are designed for single or multi-zone applications, and are currently manufactured solely by LG.

AVAILABLE OPERATION OPTIONS

Heating vs. Cooling

Do the room or rooms you’d like to air condition require just cooling or do they also require heating? If you already have a heating system, then a mini-split heating option is supplemental but not essential. But perhaps you are providing air conditioning to an addition of your home with no built-in heating. In this case you’ll most likely require a heat pump model. A basic single-zone mini-split system sometimes provides cooling only; if you would like both capabilities make sure that the model you select includes the term “Heat Pump”.

Low-Ambient Operation

If you require the special capability to provide cooling to a space with outdoor temperatures below 55° F, you will need to opt for a system with Low Ambient Operation.

Energy Requirements and SEER Measurement

If energy efficiency is important to you, there are a few ratings to keep in mind.

Energy Star Rating

Energy Star Certified models can slash your heating and cooling costs by as much as 30% than uncertified models.

EER and SEER

Two additional energy efficiency ratings to consider are EER (Energy Efficiency Ratio) and SEER (Seasonal Energy Efficiency Ratio). While both formulas are used to measure a unit’s efficiency, SEER more accurately measures a system’s efficiency over a seasonal period while EER is a better indicator of energy efficiency given one specific operating condition. The economical value of higher EER and SEER models can be significant. For instance, upgrading from an SEER rating of 9 (the lowest rating) to an SEER of 13 can reduce total power consumption up to 30%.

Voltage

Voltage may seem like a minor consideration, but matching your mini-split units’ voltage to that of your home is important; incorrect voltage can lead to poor operation, a circuit break, or in the worst case scenario, a fire. Smaller, single-zone units often run on a 110-120 volt plug – a standard wiring for most homes – while larger units require voltage between 220-240V. Before you decide on a system, check its specifications and be sure that your home has sufficient voltage to support it. If you need help, consult an HVAC professional.

MINI-SPLIT INSTALLATION

Installing Your Mini-Split System

You’ve figured out your cooling requirements and narrowed down the type of system that best suits your needs. The next step is knowing exactly what is needed to install your system successfully.

The Installation Process

HVAC Contractors

By law, a licensed HVAC (Heating Ventilation and Air Conditioning) professional is required to install your mini-split system for you. You must do your due diligence to ensure that the technician you hire is properly certified. Mini-split systems run on pressurized, electrically charged materials that can be volatile if handled improperly. Additionally, a poorly performed installation can cause operational inefficiency and system underperformance over time.

Qualified installers may not always be easy to find; make sure you can locate contractors in your area before you make any mini-split purchases. You can call us at (800) 570-3355 ext. 1634 for help with finding a certified HVAC professional in your area.

Be mindful of the fact that mini-split manufacturers provide only parts warranties. Your HVAC professional should provide you with a labor warranty so be sure to check with them about their warranty terms before contracting them.

Installation

Consultation

Prior to installing a system, an HVAC contractor should schedule an in-home consultation to view the layout of your space and determine where to place the indoor and outdoor units. It may help to have a sense of your desired placement types.

Installation Time

The simpler installations can typically be completed in under a day, but can be longer depending on how large your mini-split system is. Be sure to plan in advance with your contractor.

Cost

The cost for a mini-split installation may range significantly, as the price can vary depending on a number of factors, such as system size, unit capacity, and placement type. Check with one or more HVAC contractors to compare quotes.

REQUIRED AND OPTIONAL HARDWARE

A mini-split system requires more than just the indoor and outdoor units to operate. In most cases, these additional components are not included in the system package, so they must be purchased separately or provided by your HVAC contractor.

Refrigeration Line Sets

Refrigeration line sets circulate refrigerant between the outdoor and indoor units. A line set consists of two semi-flexible insulated copper pipes – one smaller, one larger. The smaller pipe is referred to as the liquid line and the larger pipe is called the suction line. The liquid line is measured by its outer diameter (O.D.) it usually comes as 1/4”or 3/8”. Also measured by its O.D., the suction line usually comes in 3/8” or 1/2”. Line sets are measured in feet and come in several different lengths to accommodate varied distances between the outdoor and indoor units.

When thinking about the number of line sets to purchase, remember 4 factors: number of rooms, line set diameter measurements, BTU configuration, and the distances between each indoor unit and the outdoor unit. Remember that you’ll need a line set for every indoor unit. From there, check each indoor unit’s specifications to determine the line set size for that unit’s line set. Finally, for each unit, consider the total distance that the unit will be positioned from the outdoor unit. This will determine the length you should purchase. It’s best to overestimate, as line sets can always be cut to any required length.

Condensate Lines and Drain Pumps

Like all AC units, mini-split indoor units absorb humidity that condenses into water, which then has to be pumped away. Drain pipes are part of the tubing that mini-split systems require to drain water down the piping into a receptacle such as a bucket or a flower bed. These pipes are often supplied by the contractor.

Note that for high-mounted ceiling cassette and concealed duct units, the piping often has to travel upwards. Water can’t flow upwards on its own, so these models often require a drain pump to pump the condensate away from the unit. Some brands include a drain pump for these units; if you don’t see that your model includes one; you may want to check in with your HVAC contractor regarding which pump to buy or let your contractor purchase it.

Ceiling Cassette Grills (Required for ceiling cassette units)

The ceiling cassette unit requires a grill to conduct the air from the hidden unit to the room it conditions. The manufacturer will always have a grill model to match the unit you purchase – look out for the required grill model number in the Addons and Accessories menu on the product page.

FAQs

How do I find an HVAC professional in my area?

When looking for a quality HVAC contractor, it pays do your research. You may want to search sites such as www.acca.org, or Angie’s List, which provide pre-screened listings of accredited, certified contractors. Ask around as well, as family and friends can be a great resource. Once you’ve narrowed down your options, don’t stop there. Visit the Better Business Bureau (BBB) website to research an HVAC contractor’s reviews and reputation.

Are any home modifications needed for installation?

Installing a mini-split system is a fairly straightforward process. The only required modifications are small 3-inch holes in the walls the refrigerant tubing is run through. These holes can be drilled inconspicuously, and take up far less space than a window unit or through-the-wall unit.

I live in an apartment above the 1st floor. Can I suspend my compressor unit on the side of the wall?

This is possible, as mini-split compressors may be securely mounted on an exterior wall. However, you may want to consult with your building management to be sure this is allowed before you determine mounting capability with an HVAC professional.

Can my system work in rain or snow?

Yes. The outdoor compressor is designed to operate in rain and snow.

Can I paint my mini-split units?

We don’t recommend painting your unit, as this will often void your warranty.

What is a typical mini-split system warrantee like?

Your warrantee will be separated into a parts warrantee provided by the manufacturer and a labor/service warrantee that your HVAC contractor will provide. Within the manufacturer’s warranties, the parts warranty is usually split into two separate warranty terms for the outdoor unit (compressor) and the indoor units. In most cases, indoor units will typically have 2 year warranties and compressors will have 5+ years, but be sure to review the warranty info prior to purchasing.

What are the pros and cons of a ductless split air conditioner?

Ductless split air conditioners are a cost effective choice compared to central air conditioning. They are typically more expensive than wall or window air conditioners and you need an HVAC professional to install the unit. Since the compressor sits outside, ductless split air conditioners are very quiet and efficient. The indoor units do not need to vent through an exterior wall, so ductless splits are a good option to cool rooms with no windows and no exterior walls. A ductless split system also provides more temperature control because each indoor unit can be set independently from the other units.

How do I install a ductless split air conditioner, why do I need a HVAC Professional?

Installing a ductless split air conditioner is more complicated that a window unit but far less complicated than installing central air. An HVAC professional will need to run lines for the coolant, electricity, and drainage. You will also need a HVAC professional to charge it with the right amount of coolants.

How big will the hole be in the wall?

This slightly varies depending on the unit you buy but, it is generally 3″ in diameter.

Will a ductless split system work in the winter?

If you are installing a ductless split air conditioner for all times of the year (ex: a computer/server room) you will need to purchase an air conditioner that has low ambient operation. The unit can set for cooling even when the outdoor temperature drops below 41 °F (5°C).

Do I need to purchase tubing?

Yes, you do need to purchase tubing (also called line sets) to install your ductless split air conditioner. The tubing will connect the indoor and outdoor units. The size of the tubing depends on how far the inside unit is going to be from the outdoor unit. If you are installing the indoor unit on an interior wall, you will also have to purchase a condensate pump to drain the excess condensation to the outside.

Do some ductless split air conditioners have heat?

Some ductless split air conditioners come with heat. Most work with a heat pump, but some models have electric heat strips as back up.

Still have questions about mini-split systems?

Let us know! Call us at (800) 570-3355 ext. 1634 and we’ll do our best to address your question.

OPTIONAL ACCESSORIES

These items aren’t required, but can definitely enhance your system overall.

Remote Controls

Many brands often include wireless remote controls for their wall-mount and ceiling cassette units. Double check the specs just to be sure.

Wired Thermostats

These are generally optional for wall-mounted units but often come included for concealed duct units.

Low Ambient Wind Baffle Kit

Many systems with low ambient operation operate down to 14 F – these kits allow systems to operate in cooling mode down to 0 Fahrenheit.