What Size Mini-Split Do I Need?

Ductless mini-split systems are gaining in popularity in the United States. They’ve been used in other parts of the world for decades because of their enhanced energy efficiency and flexible installation. A ductless system heats and cools your home without ductwork, which reduces air loss due to leaky ducts and increases the overall efficiency.

Whether you’re looking for a mini-split AC unit as a cooling solution for your garage or a mini-split HVAC system to heat and cool your entire home, it’s important to get the sizing and mini-split installation right.

Selecting the right mini-split heat pump and pairing it with the correct indoor units is not something you as a homeowner should undertake alone. Work with experienced HVAC contractors for the best results.

HVAC sizing refers to the amount of heating or cooling a system can provide. A unit’s size or capacity is expressed in BTUs, or British Thermal Units. It’s also expressed in tons. One ton = 12,000 BTUs.

It’s important to install the appropriately sized mini-split heat pump and paired indoor units if you want the system to offer the best energy efficiency and the best comfort.

An undersized mini-split condenser unit/mini-split heat pump or undersized indoor unit will run continuously but may not adequately heat or cool the space. This can lead to decreased comfort and higher energy bills. An undersized system can also lead to increased wear and tear and early failure or need for repairs.

Bigger is not necessarily better. Vastly oversizing the condenser unit (mini-split heat pump) can lead to short cycling, where the system turns on and off frequently. This can lead to increased wear and tear and unnecessarily high energy bills - negating the energy savings a mini-split system can provide.

Ductless systems should not be sized more than ½ ton over the BTU/tonnage that resulted in a load calculation.

The right way to size a mini-split system is with the help of an HVAC contractor with experience in the design and installation of single and multi-zone ductless systems. There are a lot of variables that a trained HVAC contractor will need to take into consideration to ensure your system is sized properly.

The size of the spaces you want to heat and cool is just one of many factors that affect accurate mini-split sizing. An HVAC contractor experienced in sizing, designing, and installing these systems will consider:

• The size of your home
• The construction materials (brick, vinyl siding, stucco)
• The climate and temperature range where you live
• Sun exposure
• The number of people expected to occupy a room or zone
• The number of windows and doors
• Ceiling height (ceiling height of more than 8’ will require more BTUs)
• Conditioned or unconditioned spaces above, below, and adjoining
• The quality of the home’s insulation
• The presence of heat-generating appliances or equipment (stoves, ranges, stereo equipment)
• And more

You’ll want to get multiple quotes on a new mini-split system. Not sure who to contact? Review our blog on how to choose the best HVAC contractor near me for some tips.

You can get a ballpark idea of what size of mini-split you need by using the square footage of the space you need to heat and cool. To calculate the number of BTUs needed per hour (BTUh), multiply the square footage of each room or zone by anywhere from 12-25.

In older homes with poor insulation and old windows and doors, the multiplier might be as low as 12. The mini-split sizing chart below uses the 25 multiplier.

But again, work with an HVAC professional for precise sizing and ask to see the results of their load calculations. The mini-split sizing chart below is for informational purposes only and should not be used to purchase a system without professional help.

In a multi-zone mini-split system, the heat pump must be sized for the entire home or space, while the indoor units must be sized for the individual room or zone. This means the indoor air handlers (also known as head units) do not all have to have the same capacity. One 4 or 5-ton Trane/Mitsubishi multi-zone mini-split heat pump can connect to up to eight indoor units.

It may sound complicated to you as a homeowner, but for an HVAC company with the expertise, tools, and knowledge, it’s not hard. The indoor units don’t have to all be the same style or mounted in the same place, either. How they are mounted can be an aesthetic choice but also can affect room comfort.

Examples include:

• Mini-split ceiling cassette/ceiling mount mini-splits
• Floor mounted mini-splits
• High wall-mount mini-splits

Your mini-split installer can help you choose the appropriate units and mounting location for each room or zone. Some common configurations include:

• Dual-zone mini-split/2-zone mini-split
• 3-zone mini-split/3 head mini-split
• 4 zone mini-split/4 head mini-split
• 5 zone mini-split/5 head mini-split
• And so on

Learn more about cooling and heating features and possibilities in our ductless systems brochure.

Trane/Mitsubishi mini-split systems are the top-selling brand of zoned ductless systems for a reason. These premium ductless systems can only be installed by HVAC contractors who have undergone in-depth training. This helps ensure you get a properly designed system that is properly installed.

Improper mini-split installation and improper design are two big reasons that homeowners have problems with their mini-split heating and cooling systems. Avoid problems and work with your local Trane dealer who is also a Mitsubishi Electric Ductless Pro Contractor. They undergo the same factory training as Mitsubishi Diamond Contractors. This makes your system eligible for a 12-year factory warranty as long as you register the system, which is two years longer than the standard registered warranty.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Ryan Goodwin, Senior Product Manager, Ductless

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