A Installing a Minisplit What you need to know about choosing a minisplit

A Installing a Minisplit What you need to know about choosing a minisplit
Installing a Minisplit
What you need to know
about choosing a minisplit
heat pump and ensuring
that it’s set up correctly
Indoor unit
By patrick Mc combe
Blower fan
lthough they’ve been around for a couple
of decades and are common in Asia and
­Europe, minisplit heat pumps only recently
have started to get traction in the United
States. A minisplit heat pump uses a refrigeration c­ ycle
to warm or cool the air inside a building. In cooling
mode, it ­extracts heat from within the building and
moves it outside. In heating mode, it works in ­reverse,
extracting heat from the outdoor air (even in very low
temperatures) and moving it to the building’s interior.
There are exceptions, but minisplits generally don’t
have ductwork. Instead, a minisplit has an air handler
and a refrigeration coil in a self-contained wall-mounted
or ceiling-mounted unit. Temperature and fan speed
generally are controlled with a handheld remote, but
they can be operated with a wall-mounted thermostat.
When they were first introduced to this country, minisplits were thought of as an add-on to a central heating
and cooling system and a way to condition hard-to-cool
spaces. More recently, they have become an efficient way
to heat and cool entire houses, often for less installed cost
than a central system with ductwork. Here, I’ll answer
the most common questions about minisplits and will
walk you through a typical installation so that you know
what to expect when the HVAC tech shows up.
Patrick McCombe is an associate editor. Photos by
the author.
Outdoor unit
A minisplit is a split
refrig­eration system,
Power to
indoor unit
with an indoor air handler and an outdoor unit
that houses the compressor. These systems
are mini because they
are much smaller than
typical central air conditioners or heat pumps
Condensate line
(9000 to 15,000 Btu for
a single minisplit vs.
30,000 to 60,000 Btu for
a central air conditioner
or heat pump).
Refrigeration lines
Service valves
Drawing: Don Mannes
Installation starts with the indoor unit
The indoor unit hangs from a metal bracket that’s attached to wall framing with screws.
The unit’s refrigeration and condensate lines run through a 3-in.-dia. hole adjacent to
the bracket. The bracket must be hung level for aesthetics and so that the condensate
drains properly.
Is a minisplit less expensive
than a furnace or a boiler?
Maybe. The smallest 9000-Btu
system can be found for under
$1000. Installation runs several hun-
Extras add to the cost.
Beyond what’s supplied
by the manufacturer,
the installer needs
enough refrigeration
line and 14-ga. fourconductor cable for
connecting the indoor
units to the outdoor
unit. Every indoor unit
also needs enough
condensate tubing to
reach outside or to an
interior drain. Every
outdoor unit needs a
wall bracket or pad
for mounting.
dred dollars more. A whole-house
turnkey system with normal installation conditions costs anywhere from
$2000 to $10,000 and depends on
the number of indoor and outdoor
units, the complexity of the installation, and l­ocal labor rates.
Is the installation
No. Retrofit installations take about
a day. The installer drills a 3-in. hole
through the wall near the indoor unit
for the two refrigeration lines, the
condensate line, and the electrical
cable. After mounting and connecting the indoor and outdoor units, the
Made for easy
mounting. Using
the instructions
to determine the
right location, the
installer drills a 3-in.
hole for running the
refrigeration lines,
electrical cable, and
condensate tubing
to the outside. The
bracket is then leveled
and mounted the
specified distance from
the hole. The bracket
should be attached to
two studs.
installer clears the refrigeration lines
of air, tests for leaks, and charges the
lines with refrigerant.
Can I install a minisplit
At a minimum, clearing the
refrigeration lines of air and water
vapor requires a vacuum pump
($200) and a refrigeration manifold
gauge set ($150). Depending on the
distance between the indoor and
the outdoor units, you also may need
to add refrigerant, which requires
a precision scale to measure accu-
Connections require
access. The indoor
unit’s short lengths of
refrigeration tubing and
condensate line must
be extended to reach
the outdoor unit. If the
head is on an outside
wall, the extended lines
are run on the outside
of the building. If the
unit is on an interior
wall, either the lines
need to be roughed in
before the drywall is
hung, or a hole needs
to be cut to extend
rately. Finally, to buy and handle the
refrigerant, you need training and
EPA certification.
Can a minisplit heat and
cool my entire house?
Multiple minisplits can heat
and cool a home of any size in all but
the country’s very coldest regions.
Comfort with a single unit assumes
a small, superefficient home with a
compact footprint. Some homeowners with a single minisplit have com-
Continued on p. 77
energy-smart homes
cables and Tubing are routed outside
The indoor unit is connected to the outdoor unit with a pair of refrigeration lines and an
electrical cable. The lines and the cable can be hidden within walls or inside a plastic covering
called line-set ducting. The lines also can be left exposed on the building’s exterior.
Line sets should take a direct path. Pairs of insulated soft copper
tubing make up the refrigeration line set. In this installation, the
line set, four-conductor cable, and condensate tubing run from the
indoor head toward the outdoors through an attic crawlspace. The
bundle of tubes and wire requires a 3-in. hole that will be sealed
later with duct-sealing compound for weathertightness.
Reflare the fittings. The copper refrigeration lines have
flare connections. The line sets come preflared and with
their own flare nuts, but manufacturers recommend
removing these nuts and reflaring to accommodate the
flare nuts that come with the indoor and outdoor unit.
Condensate line runs downhill. Condensation produced during
cooling mode is drained to the outside or to an interior drain
through a 5⁄8-in. flexible hose. The hose should slope a minimum of
⁄4 in. per ft. for its entire length. When there’s no way to drain the
water via gravity, condensate pumps within the head or mounted
externally can pump the condensate outside or to a drain.
Power comes from the outdoor unit. The indoor unit is powered
by the outdoor unit through a four-conductor 14-ga. cable. The
stranded cable is as flexible as an extension cord, so it’s easy to
run it and to make the connections. Some versions have reinforced
UV-stabilized jackets, so they can be left exposed without a
protective conduit.
Mounting the outdoor unit
The outdoor unit, which houses the compressor and the control circuitry,
requires 220v AC power for operation. By code, the power supply must include
a “service disconnect” with a 110v receptacle so that HVAC technicians can
power their service equipment or turn off the power during repairs.
Continued from p. 75
plained that the upstairs sometimes
gets too hot in the summer. For more
even temperature distribution, it’s
best to have one unit upstairs and
one unit downstairs. In this scenario,
the upstairs minisplit does most of
the cooling, and the downstairs unit
does most of the heating.
Secure the outdoor
unit. The outdoor
unit either is screwed
to a small concrete
or plastic slab on the
ground, or is attached
to wall-mounted
brackets. In both cases,
the outdoor unit should
be installed above
the anticipated snow
level. If it gets buried
in snow, the unit will
freeze up and stop
Are minisplits one size
fits all?
The unit size depends on the
size of the space you’re planning to
heat and cool, the space’s insulation
and airtightness levels, and your
climate. Code requires the HVAC
technician to perform a Manual J to
account for all of these factors.
Are minisplits reliable?
Yes. Unlike a conventional central
heating and cooling system, which
is comprised of dozens or even hundreds of parts from multiple manufacturers that are then assembled
on-site, a minisplit has matched
components that require very little
on-site assembly. Also, there’s no
fine-tuning of the components (a
process known as commissioning), as
there is with a conventional central
air-conditioning or heating system.
Plan for noise. A
minisplit’s outdoor
unit is surprisingly
quiet, but it should be
located so that it’s far
from bedroom walls,
bedroom windows, and
outdoor living spaces.
The wall brackets
shown have rubber
mounts for reducing
vibration and noise that
can travel through the
house’s framing.
Will a minisplit work on the
coldest days?
Maybe. Conventional heat pumps
typically employ backup electricresistance heating around 40°F to
make up for the lack of available heat
in the outdoor air. A cold-climate
minisplit model such as the Mitsubishi HyperHeat can deliver 100% of
its rated output down to 5°F. At –4°F,
the heating capacity drops to 82% of
the rated heating capacity. At –13°F,
the heating capacity drops to 62%.
Will a minisplit improve the
comfort of my home?
Minisplits are great for
Continued on p. 78
energy-smart homes
Continued from p. 77
heating and cooling spaces that
Connecting the outdoor unit
The copper refrigeration lines are attached to the service valves on the outdoor unit
with flare connections that are the same size as those found on the indoor unit. The
220v AC power and the cable that powers the indoor unit also must be connected.
are tough to make
comfortable, such
as bonus rooms over garages. They
offer more-even heating and cooling
because of their variable-speed compressors and multispeed blowers.
But they’re unlikely to solve comfort
complaints related to drafts and
air leakage, and they won’t reliably
heat or cool spaces far from where
they are located.
Do I have to remove my
existing heating system?
No. In fact, it’s generally a good
idea to preserve your existing sys­
tem as a backup for especially hot
or cold spells or if something goes
wrong with the minisplit. If you’re
Outdoor connections look like indoor
connections. The copper refrigeration lines
running from the indoor unit are connected
to the outdoor unit with flare fittings. As
before, the flare nuts installed on the line
set are removed and replaced with the nuts
provided by the minisplit manufacturer.
Checking for leaks. After the copper lines
are connected, they’re pressurized to about
300 psi with nitrogen to test for leaks. In
addition to watching for steady pressure on a
manifold gauge, the fittings are coated with
a refrigeration-specific soap solution. Any
bubbles around the fitting indicate a leak.
replacing a failed conventional system that has ductwork, it makes
sense to remove or seal off any ductwork running through unconditioned
attics or crawlspaces. Afterward,
plug any holes that connect conditioned and unconditioned spaces.
Will a minisplit save me
Minisplits can certainly
heat more affordably than electricresistance heaters. At an outdoor
temperature of 30°F, a minisplit
provides three times the amount of
Power requirements
are reasonable.
Powered by a 20A or
30A circuit, depending
on its Btu output,
the outdoor unit gets
its energy from the
disconnect switch
through conductors
run within a flexible,
watertight conduit
called a whip.
heat as an electric-resistance system
for the same amount of money. Also,
if you’re cooling your entire house
with conventional central air, multiple minisplits likely will be cheaper
to run because of their more-efficient variable-speed compressors
and more-nuanced zone control.
The payback in energy savings for a
whole-house system, however, could
take so long that it’s not worth making the switch until you need a system replaced.
Evacuating the line set
to prevent problems.
Before the service
valves are opened and
the 410a refrigerant
in the outdoor unit
is released, the
refrigeration lines must
be evacuated of air
and water vapor with a
vacuum pump.
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