Ductless mini-split air conditioning systems are gaining popularity
nationwide and especially in coastal communities. Tom Antolick of
BTU Control, an HVAC installer in the seacoast community of
Edgartown, Mass., reports that ductless has grown from a small
percentage of his business to about 20% in recent years. "They've
become hugely popular. I now sell 40 to 50 of them per year." The
reasons: They're quiet, energy efficient, easy to install, and easy
to zone. And in an ocean environment where high humidity is the
main cause of discomfort in the summer, these units are as
practical for dehumidification as for cooling.
Two in One
Think of a "ductless mini-split" as a sort of hybrid between a
central and a window air conditioner. It consists of small outdoor
condenser unit and one or more indoor evaporators. The term "mini"
refers to the small indoor units, which mount on the wall or
ceiling. Each evaporator cools a single room, although some
homeowners opt to cool an entire home by installing a number of
these units. Refrigerant is piped from the condenser through
small-diameter insulated refrigerant lines directly to individual
rooms or zones. A fan in the evaporator blows cooled air into the
Ductless mini-splits have been common for decades in Europe and
Japan, where most homes lack the ductwork needed for central air.
Worldwide, in fact, there are far more ductless than ducted
systems. According to Carrier's Tom White, these systems debuted in
the U.S. in the mid-1980s, primarily in commercial buildings, but
since then they've taken a growing share of the residential market.
Paul Drosness of Sanyo Fisher estimates that Americans buy about
125,000 ductless systems each year.
While that's still peanuts compared with the millions of systems
sold in other countries, it represents a solid foothold. "The
product is becoming accepted in the U.S., and it really seems to
have caught on in the last three years," says Friedrich's T.J.
Wheeler. In fact, while the ductless has always been thought of as
a retrofit technology, manufacturers and installers report a
growing number of these systems going into new homes, especially
those with radiant floor heating.
Cons and Pros
Cost. Ductless systems aren't cheap. The
U.S. Department of Energy (DOE) estimates equipment costs of about
30% more than central systems. But the numbers don't tell the whole
"Equipment costs may be more expensive," says Mike Smith, a
marketing manager at Mitsubishi. "But there are applications where
ductwork simply isn't practical." And the DOE numbers don't include
the cost of ductwork. "It used to be that ductless systems weren't
cost effective," says Jonathan Duncklee, vice president of Duncklee
Cooling and Heating, an HVAC contractor in Stonington, Conn. "But
the cost of steel has gone up so much that they're more likely to
Regardless of whether a ductless system makes sense for whole-house
cooling, it's still a good spot-cooling system for a couple of
rooms. Antolick says that a simple installation of a single
condenser/evaporator combination usually costs the customer $2,400
to $2,600 installed. A dual-zone system costs about $3,800
installed, and a tri-zone roughly $5,000.
Aesthetics can also be a sticking point
for some customers. Duncklee's company works on expensive homes on
the Connecticut shore. He says that while most people find the
indoor evaporator acceptable, he occasionally runs into someone who
doesn't want to look at it. Some contractors have tried recessing
the units into the ceiling and putting grilles over them, but
Duncklee doesn't recommend this. Because the unit draws air in
through the face and blows it out the bottom, recessing the unit
can only make it less efficient by restricting airflow. A few of
his customers have built cabinets around the indoor units, but the
cabinet doors have to be opened before turning the unit on.
Ductless systems consist of an indoor evaporator and an outdoor
condenser. Indoor units can't easily be recessed into walls or
boxed into cabinets without constricting airflow.
There's also the issue of how to hide the refrigerant lines that
run from the indoor to the outdoor unit. Antolick uses a product
called Slim Duct. It's basically a white vinyl channel that houses
the lines. Depending on the type and color of the siding, the
housing can look obvious, but it's better than copper pipe.
Duncklee uses white downspouts, to match those on the rest of the
house. (Inside the house, the issues are the same as running
plumbing pipe: Both lines run through closets and basements, where
they won't be seen.)
But contractors who use mini-splits say their advantages far
outweigh any challenges posed by cost or aesthetics. These
Easy installation. Because there's no ductwork,
installation is simpler than for central air. The only holes that
need to be made in the house are small holes for the refrigerant
lines and electrical wires, along with drains to carry condensation
from the evaporator to the outside. That makes the mini-split a
good choice for sunrooms, garage conversions, and existing homes in
which adding ducts would be expensive and disruptive.
Silent operation. Ductless is a good choice for
clients who crave quiet. While a ducted system has to be sized just
right if you don't want to hear the rush of air through the ceiling
grilles, the evaporator on a ductless unit is nearly silent. That
makes it a good choice in a bedroom or a media room, where you
don't want a lot of background noise. The outdoor condenser is
quiet enough to put on a patio. Compare that with a standard 10
SEER central unit, which is rated at 80 db. Lennox makes a
super-quiet model that puts out only 69 db. "Mini-splits are even
quieter than that," says Antolick.
Simple zoning. Zoning a ducted system can be a
complex job. But that's not the case with ductless. Each evaporator
is connected to the condenser with a dedicated refrigerant line,
and each one comes with a hand-held remote and can be hooked up to
its own standard or setback thermostat. Some condensers are
designed to serve two or three evaporators.
Precise cooling. Mini-splits are a good choice for a
room addition or a small cottage. The smallest central air system
has about an 18,000 Btu capacity, which isn't efficient if you have
less than 1,000 square feet or so. Mini-splits, by contrast, start
as small as 9,000 Btu.
Heating. Some of these systems include a heat-pump
mode, so they will warm the house during the cool months. They
usually put out enough heat for all but the coldest months in the
Northeast, making them perfect for a seasonal beach home. And
according to Smith, they will produce more heat at colder outdoor
temperatures than a standard heat pump. Mitsubishi's system, for
instance, will heat to full capacity down to 47°F, and will put
out 70% of its maximum capacity at 17°F. "Mini-splits are a
good choice where the design temperature for that region is
32°F or above," he says. "You can use electric heat for the
days or weeks you fall below that temperature."
Efficiency. In recent years,
manufacturers have introduced modulating condenser motors to the
U.S. market. Rather than turning on and off to keep temperatures at
the thermostat's set point, the motor varies its speed gradually,
letting it maintain precise temperature the same way that the
cruise control on a car maintains a constant speed. These units are
quieter and use less energy than conventional ones. And because the
motor isn't constantly starting and stopping, there's less wear and
One of the most valuable features for coastal climates is the fact
that some systems will dehumidify without cooling. They do so by
cycling air through the evaporator at a very low fan speed.
Mitsubishi's M-Series has a variable-speed fan that runs
continuously at a low level. "It runs all the time but modulates up
and down," explains Smith. "Built-in microprocessors tell the fan
the optimum speed." In Fujitsu's system, by comparison, the fan
comes on and off intermittently while the evaporator is off, using
stored energy in the cold coil to take moisture out of the air. And
because the volume of air going across the coil is less, it only
lowers temperature a degree or so, according to Fujitsu's Roy
Kuczera. "That's a lot more efficient than a central unit, which
usually needs a reheat coil [to do dehumidification]."
Outdoor condenser units can handle up to
three zones. Although a mini-split system saves the expense of
installing ductwork, the channels carrying the refrigerant lines
and condensate drains are quite conspicuous.
To those who wonder how well the outdoor unit will stand up to salt
air, Friedrich's Wheeler points out that ductless mini-splits are
the cooling system of choice in most of the Pacific Rim. "Those are
tough climates, and ductless is all they use." He names a handful
of features designed to prevent corrosion from salt air:
• Most good ductless units have a plastic fan blade instead of
the metal one typical of central air systems.
• The condenser motor's horizontal orientation means the
openings on the motor aren't pointing upward, ready to catch water
• The condenser motor is small enough that it can be totally
enclosed and still kept cool.
• All of the base pans in the outer portion of the unit are
painted or powder-coated to protect them from corrosion.
A worker joins two lengths of the tubing that will carry condensate
away from the house.
Some manufacturers, like Mitsubishi and Fujitsu, will put a
corrosion-resistant coating on the coils as an option, but not
everyone thinks it worth the extra expense. "We used to have [a
similar coating] but discontinued it," says Drosness. "I don't
think it's necessary. I have one account in Bermuda, and I never
heard of a unit having to be replaced because of corrosion from
salt air." ~
Charles Wardell writes on construction topics from Vineyard Haven,
Mass. All photos by the author except where noted.