How to Install a Wall-Mounted Mini-Split | Ask This Old House

In this video, plumbing and heating expert, Richard Trethewey explains the purpose of a mini split ductless air conditioner and the process of getting one installed.

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How Does a Mini Split Work?
It’s simple physics—heat will always transfer to cold. Using something called an inverter, the mini split is capable of capturing heat through a cold line of refrigerant and moving it to the desired location.

In the summer, the heat is extracted from the air in the house and dumped outside, making it cold. In the winter, heat is scavenged from the outside and pushed back into the house. This creates heating and cooling year-round.

Because there are no ducts to retrofit, the system is simple for a pro to install. And it provides excellent dehumidification, quiet operation, and great efficiency. Need to adjust the temperature or turn the unit off? Just use the remote control.

How Much Space Can a Mini Split Cool?
A single air handler can heat or cool up to 1,000 square feet, depending on the climate and system size. (In heating mode, it functions down to minus 13 degrees F, not a problem where you live.)

For larger spaces, up to four independently controlled indoor units can connect to one condenser, for the ultimate in zoned comfort.

Time: 4-6 hours
Cost: $2,000 – $15,000
Skill Level: Professional

Where to find it?
Richard installed a 12,000 BTU SEER Ductless Mini Split Heat Pump System [], which is manufactured by LG (

Installing a mini split is an involved process, so Richard recruited the help of Boston Standard Plumbing for the installation (

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About Ask This Old House TV:
From the makers of This Old House, America’s first and most trusted home improvement show, Ask This Old House answers the steady stream of home improvement questions asked by viewers across the United States. Covering topics from landscaping to electrical to HVAC and plumbing to painting and more. Ask This Old House features the experts from This Old House, including general contractor Tom Silva, plumbing and heating expert Richard Trethewey, landscape contractor Jenn Nawada, master carpenter Norm Abram, and host Kevin O’Connor. Ask This Old House helps you protect and preserve your greatest investment—your home.

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How to Install a Wall-Mounted Mini-Split | Ask This Old House