Remodeling with Ductless, Mini-Split Heat Pumps

Ductless mini-split heat pumps make room additions and HVAC replacements on small homes easier

March 31, 2008

The mini-split system allows the homeowner to heat or cool select rooms within the house rather than the entire house.
Illustration by Tom Rybarczyk

Ductless mini-split heat pump systems provide an excellent way to heat and cool a room addition, a basement remodel or even a small home. They combine the flexibility of room air conditioners with the efficiency and comfort of central HVAC systems, and they don't require ductwork, which makes remodeling quicker, easier and less intrusive.

Your client will also be pleased with the overall aesthetics compared to window units, because you won't need to block windows.

"Wherever a conventional system can't easily go, we use ductless mini-split heat pumps," says Donnie Potter of Potter Heating & Electric in Waldorf, Md.

S.D. Lohr, an award-winning remodeling firm in Waldorf, Md, uses mini-splits in single room additions and sunrooms.

"They are cost-effective to put in and clients love them," says Tina Lohr, co-owner.

How They Work

Mini-split systems — so named because small indoor units are located in each room or zone — operate like conventional heat pumps with outdoor condensing units and indoor fan coils. With mini-splits, refrigerant is piped directly from the outdoor unit through small-diameter insulated refrigerant lines. It goes to an individual evaporator unit and air handler mounted in the room that you're cooling or heating. A quiet fan blows the indoor air across the cooled or heated coil and then directly into the room. Each room or zone has its own thermostat.

With a conventional heat pump, refrigerant lines run from the outdoor condensing unit to a central indoor evaporator coil, where the air is heated or cooled. The conditioned air is then distributed through ductwork branched off to various rooms, which may or may not have separate zone controls.

In the mini-split system, the refrigerant lines that run to each fan coil unit take up much less room than typical ducts, which makes installation easy in a retrofit.

In-room air handlers can be mounted almost anywhere. The wall-mounted units are easy to install and maintain.
Photos courtesy of PATH Partners

Where They're Used

At first, ductless mini-split heat pumps were installed primarily for cooling. Now they often provide heating for year-round comfort.

And like conventional units, it is important to size mini-splits appropriately.

"We always do the Manual J [Air Conditioning Contractors of America's residential HVAC Manual J load calculation] for the whole house," says Lohr. "If the existing system can't handle the new load, we'll replace the whole thing and size it appropriately if that makes economic sense. If the existing HVAC is new and working well, we'll use the ductless mini-split for the addition."

Coleman & Laurienzo Builders, of Damascus, Md., uses ductless mini-split heat pump systems in its Classic Addition (profiled in Professional Remodeler January 2008). The mini-split is a small, quiet and easy-to-install HVAC system that is compatible with the packaged approach Coleman & Laurienzo uses when adding great rooms.

Ductless mini-split heat pump systems are increasingly versatile. Mitsubishi now supplies a system in which one outdoor unit can service up to four zones.

"This system is good to use in multiple rooms when installing ductwork is not possible," says Potter. "Take for instance a small beach house on a slab with a too-small attic. An air handler can be installed in each room of the house. And no ducts."

Installation and Operation

The outdoor unit is slim and requires minimal ground or service clearance and can be installed wherever it is convenient for the remodeler and the homeowner.

Ductless heat pumps are installed using conventional methods for heat pumps and air conditioners. Unlike ducts, which are bulky and require special structural consideration, split-system piping can often be routed through walls and joists. Just make sure to insulate both service lines.

The indoor air handling unit can be installed on the wall, flush-mounted or suspended from the ceiling. Ductless units are easily connected by refrigerant lines running through a small opening in the wall or ceiling.

"It's pretty quiet anyway, but one of the great things is that you can move the outside unit away from the building if noise is an issue," says Lohr.

With a minimum SEER of 13 and a minimum HSPF of 7.7, split systems are also an energy-efficient choice, especially when you consider that many systems far exceed those minimums. According to Potter, all Mitsubishi ductless heat pump systems two tons or less are 16–17 SEER. Also, system energy losses are lower because distribution takes place through insulated refrigeration lines rather than ductwork (which is often leaky and can account for a third of the energy usage for heating and cooling). According to the NAHB Research Center, distribution energy losses in conventional systems have been as high as 30 percent, while distribution losses for ductless systems are about one to five percent. And because each zone has its own thermostat, occupants can modify temperatures in a particular part of the house. The ability to control each zone separately can also lower your clients' energy bills.

What's the Price?

The cost of ductless heat pumps has declined as the technology has become more established in the market. The NAHB Research Center's 2004 poll of ductless heat pump suppliers showed material costs for ductless heat pumps between $500 and $900 per ton, depending on the type of system and the number of zones desired per unit. S.D. Lohr's systems generally cost about $2,500 installed for a 1½ ton system.

"When you include the cost of ducts, the ductless heat pumps are always less expensive than the alternative — and quicker to install," says Potter.

Glen Salas writes about better building practices on behalf of the Partnership for Advancing Technology in Housing (PATH). PATH is administered by the U.S. Department of Housing and Urban Development. Learn more at

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