What is Ductless

“Ductless? So where do the ducts go?”

  • It’s not hanging out in your dusty attic or your damp crawl space deteriorating and leaking.
  • It’s not collecting dirt and mold from years hanging out in your attic and crawl space.
  • It’s not coming apart from failing duct tape and sucking in dirt and fiberglass.
  • It’s not getting chewed on by critters making bigger holes for more dirt and fiberglass.
  • It’s not inefficient.
  • It’s not wasting your PG&E bill heating and cooling your attic and crawl space, and critters.
  • It’s not loud.
  • It’s not expensive.

A simple single zone Mitsubishi ductless system is made up of three components:


  • The indoor section
  • The outdoor section
  • And a wireless remote controller

The indoor and outdoor units are connected by four lines: two small refrigerant lines (continuous copper tubes that are insulated), a power and control cable about the size of your finger, and ½” PVC condensate line. In most installations these four small lines pass through a 2 ½” to 3” hole in an exterior wall behind the indoor unit. On the outside, the lines are run down the wall in a neat cover that closely resembles the downspouts on your home. Those lines are run to the outdoor unit mounted on a supplied base that sits on the ground.

Instead of air moving through the lines (as in a duct system) a refrigerant (which contains the heat) moves between the indoor and outdoor units. In cooling mode the heat moves from the indoors to the outdoors. To heat the home the process is reversed.

The indoor unit contains the blower, filtration, and airflow controls (directional vanes) and draws the room air in from the top (on high wall mount units) or the center (on ceiling recessed units). It then distributes either heated or cooled air through the directional vanes into the room or space.

Since there is no ductwork, there are no duct losses. This is one of the great advantages of the Mitsubishi ductless air conditioning and heating systems.

Duct losses come in three types: leakage, thermal, and static pressure.

  • Leakage is obvious:
    Holes or separation in the ductwork let expensive conditioned air go where you don’t want it. Or that same leaky ductwork will draw in dirty, unconditioned air to mix with conditioned air to rob you of the money you spent conditioning it. Most duct systems eight years or older leak on average 25%-45%, and many of them even more. That is a huge waste of energy and money. If you’d like to see what your losses are, schedule an appointment with Rio Vista Air for a free analysis.
  • Thermal losses are sneakier:
    They come right through your ducts whether they are leaky or not. Most ducts have only 1” to 3” of insulation on them. Your attic on a hot summer day your attic can reach 140 or more. While in your home your air conditioner is trying to maintain a comfortable 75〫. That is a huge 65〫 temperature differential. The 13” or so of insulation above your ceiling is doing a good job of keeping the heat out. But what about the 1” to 3” on your ducts? You guessed it, the heat is racing through robbing you of your expensive conditioned air.
  • Static pressure:
    In a duct system, static pressure, in simple terms, the energy required to move the air through the ducts. A properly sized, well designed duct system has relatively low static pressure. A poorly designed duct system, something found in a lot of in attics, can have excessively high static pressure robbing airflow and capacity and increasing your energy bill.
    What is the best way to counter duct losses? Do away with ducts! Call Rio Vista Air and have us evaluate your current system to let you know how much you could be saving on your PG&E bill with ductless technology by Mitsubishi.
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(707) 374-5992

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