When to Install a Ductless Air Conditioning System

What’s the Difference Between a Ducted and Ductless Air Conditioning System?

Air conditioners provide cool air through two forms of delivery: ducted or ductless systems. The majority of homes in the U.S. are built with air ducts made from sheet metal that run from the main air conditioning unit to each room in the house. The ducts are hidden in walls and air is delivered to each room through vents. In ductless systems, the refrigerant from the outdoor condensing unit is sent directly to an air handler located on the wall or ceiling of a particular room.

While a ductless system can have several benefits, many homeowners with existing ductwork will be better off from a financial and comfort perspective by using a ducted system.

Benefits of Ductless Air Conditioning System

  • Easy for a contractor to install (no ductwork)
  • Some flexibility in location of air handler
  • Ability to cool the home by specific zones
  • Quiet when operating

Concerns with Ductless Air Conditioning System

  • Reduced overall indoor air circulation and increased humidity can lead to comfort and air quality problems
  • Appearance of the air handler on a wall or ceiling in each room
  • Higher cost of ownership for a whole-home solution if your home already has central AC
  • External refrigerant lines which could cause energy losses and aesthetic concerns
  • Serviceability and ease of repairs could be a problem as the unit gets older

When to Consider Installing a Ductless Air Conditioning System

While we don’t recommend a ductless system for most homes, there are several situations where a ductless system should be considered over a traditional ducted one. These include:

  • Room additions or adding cooling to a garage or work space
  • Cooling smaller, older homes without existing ductwork
  • When space is at a premium and ducts won’t fit
  • When replacing a less efficient window/room air conditioner

The bottom line on Ductless Air Conditioning Systems

Your comfort, humidity and long-term reliability should all be factors in making a smart decision. As with any important HVAC question, it makes sense to talk with a professional. Contact a reputable licensed contractor who can explain the many options and variables when it comes to selecting the best solutions for your needs.

If you’re considering a ductless system, comment below and tell us some of the reasons it appeals to you!

For more information on ductless systems, click here.

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33 thoughts on “When to Install a Ductless Air Conditioning System

  1. Hello,
    I really need your advise.
    I’m a teacher who works in a small enclosed space with no windows and an extreme heat. Our scool is old and
    A/C unit doesn’t work. If other rooms have windows, my small enclosed space doesn’t. What should I do to relieve my and my students’ suffering? I’m thinking about a small portable unit without the hose and any connection to window.

    • Hi Tanya – The first thing you might want to do is ask about proper ventilation to and from that space. Being in an enclosed space is ok as long as you have proper make-up air which should also help you regulate the temperature. If you only have a vent coming into the space and no return air vent then they are assuming you are leaving the door open so you can use the vents in the hallway or in another room nearby. You might try moving more of the hot air out of your space by putting a box fan near the doorway to move the hot air out into the hall. Once you figure out the airflow situation you can then move on to finding the controls for the air temperature coming into your room in the hope that you can regulate it. If that is unsuccessful, maybe you can regulate the incoming air by partially blocking the vent coming into your space. Portable AC units might work. Other mini-splits or through the wall units will require modifications to the walls but these might offer a more permanent solution, albeit at higher cost. I hope this helps. Thanks for visiting our site.

  2. I have a brick twin house in PA. It was built in the 1920’s and does not have any duct work. Our heating system is a boiler with radiators and we have to use window AC units in the summer. Would it make more sense to keep using Windows units or to get a ductless system installed?

    • Hi Mark – I will base this answer on most of the posts we have seen on this site and some of my own experience. In general, mini-splits can represent a large improvement over window units for many reasons (window access, efficiency, heat pump options, etc., to name a few) but they are more expensive than window units and not really a DIY solution for most people like window units can be. Central systems in turn offer some benefits over mini-splits (better air circulation and filtration, better humidity control, no units hanging on the walls, etc) but getting ductwork into a home that has none and has boiler heat can be a trick too. I put central AC into my 1920’s home with boiler heat and the cost was actually less than the quotes from the mini-splits. I had to put the air handler in the attic and gave up some second story closet space to run ductwork to the first floor from the attic but I have been happy with that solution.

      For cases like this we usually recommend getting a few different quotes for both central ducted and mini-splits and before deciding. You might also consider just adding a zone at a time or using a mix of central, mini-splits and/or room air for different locations. Maybe a small central system combined with some mini-splits in key, hard to get areas might be one option. Bottom line is that it takes a while to get different contractors to look at unique jobs like this until you find one that is on the same page as you on the job so plan on that. As we are nearing the end of the cooling season (I hope) you should have time to do this research. I hope this helps answer your questions. Thanks for using our site!

  3. I had never heard of this system. I have an older motor home that needs an ac replacement and with interior fans, wouldn’t this be a good alternative to installing a new ducted ac?

    • Hi Elsa – a mini-split might work on a mobile home but it would not be very “mobile” if you have to move it. The outdoor unit usually sits on the ground outside the home but you might be able to attach it some other way. There are some other specialized mobile home HVAC systems you might want to consider as well. I hope this answers some of your questions.

  4. Hi Kay – options for this small space in an arid location would be, in order of increasing cost: “window” or “room”” AC installed in a window in the room – you can buy at a local retailer and probably install it yourself or have someone do it for you. The next would be a through the wall PTAC system like you see at hotels. this is a little more expensive but you get to keep your window functioning without an AC unit sitting in it. The next step would be a mini-split system with s separate outdoor unit and the indoor cooling unit hangs on the wall or in the ceiling. Both the mini-split and the PTAC would require a good contractor to size the unit and handle the installation.
    I hope this helps to answer some of your question.

  5. I would like to buy an a/c unit for my parents who live in the high desert of NM, it is extremely dry, there is no humidity to speak of. They do not have central A/C and need to cool a room with unfortunately high ceilings (but with a ceiling fan). They will not want to run an exhaust hose out the window; but do they need to? Please advise me on what’s best–10,000 btu, portable unit? That is what I’m thinking unless you have another suggestion. Many thanks.

  6. My name is Michael Brooks.I want to know if you can get me this Air Conditioners to purchase without installation.

    4 ton 410-A 14 seer condenser

    4 ton 410-A coil

    50 foot 7/8 lineset

    Kindly send me the pricing plus tax for the above material .Also let me know the major credit cards you accept for payment.I will look forward for the pricing.I need your contact details in case of any future reference.Also let me know if you sell water heaters.

    Regards,

    Michael Brooks

  7. I didn’t realize there were external lines with a ductless system. That seems like a deal breaker to me. My wife and I are building a home and working on the plans. It seems like zone-specific cooling would be really nice, but I don’t want to lose curb appeal. Thanks for the information.

  8. I have a sun room. Home built in 1928 CA. II asked for bids for a split unit.
    contractor 1. Mitsubishi # MSZGE36NA-8 17,200BTU & #MUYGE36NA1
    contractor 2. Mitsubishi # MSZHE24NA & MUZHE24NA (18 seer)
    space about 2000 sq ft.
    What is the difference between SEER and BTU. Which is more important?
    Contractor 2. Has also quoted for Mitsubishi 19 SEER high efficiency 2 ton heat pump system. And 14.5 SEER 3-ton pump system.
    Totally confused.
    Thanks

    • Hi AJ – here are a few things to consider.
      SEER (Seasonal Energy Efficiency Ratio) is an efficiency rating. This is a rating based on an average load over a typical annual season of operation – weighted by the amount of time spent on “high load” –e.g. imagine the hottest day of the year in the afternoon and the time spent running at night and in the fall and spring. The efficiency varies based on these load conditions so the DOE has selected a weighted average range for the US to judge/rate various systems. Higher SEER systems usually cost more than lower SEER systems for the same capacity (BTU/Hr).

      BTUH (BTU per hour, or British Thermal Units, or “tons”) is a measure of capacity or how much space the equipment can cool (along with adjustments for things like your insulation, shade, leaks, R value of windows, door, etc.). Larger capacity systems usually cost more than smaller systems.

      One really important thing you and your contractor need to consider is how much capacity (BTU/Hr) you need. If you get too much capacity you will not have enough run time to keep the air moving in your space and you will lose the benefits derived from keeping the air moving across the cold coil to remove humidity and across a filter to remove pollen, debris and other contaminants. Conversely, too many BTU’s will yield short run times and poor air quality. If you size it too small, your system will not keep up on the hottest days.

      Good contractors can do calculations to spec out the size of your unit to match your needs. If they don’t do calculations or do them poorly you might have worse air quality and humidity problems. A variable capacity system (with variable refrigerant and air flow) might be a little more forgiving but the principles are the same. The capacity needs to be right for the worst day as well as the light load conditions. Good contractors should be able to explain this to you.

      BTW, Efficiency ratings like SEER are simply measures of how much energy it will take to cool your space. The ratings are comparable from one system to another based on the standard testing procedures. Generally higher SEER ratings will yield improved electric energy savings depending on how you run the system. For example if you have a high SEER system and have a hot summer and keep the thermostat really low you will burn through a lot of electricity. If you have a lower SEER system and have a cool summer and keep the thermostat high for extended periods you might use less electricity. High SEER does not always mean lower operating cost. Energy costs also depend on how you operate it.

      On this site we recommend getting 2-3 quotes from various qualified contractors who do the right calculations and recommend good options for your space. Find someone who can explain all this to you and help you make the right decisions. Here is a link to a contractor organization we support and has a contractor locator app.

      https://www.acca.org/locator

      It is a good if you can find a contractor who is on the same page before deciding. It might take a while but our research shows you will be more satisfied with your system decision if you are satisfied with your contractor doing the installation/service.

      Good luck with your HVAC project!

  9. Thanks for the helpful blog and forum – lots of useful information here. We decided to convert our garage into living space recently so needed to decide on an HVAC system. I am a general contractor so I have been involved with the placement of various types of HVAC equipment in lots of homes. I figured that a ductless mini-split heat pump would be the easiest and cheapest to use but all the quotes that came in for mini-splits were about the same as the ones I got for adding a small central AC/heat pump system with the air handler and ducts in the rafters above the space. The ducted system was actually cheaper than the ductless after all said and done… $4600 for the ducted system and $6k+ for the ductless.

    We did not have a lot of space to mount the wall units anyway and running condensate lines in the ceiling was difficult to due to the space available. It gets humid here in the summer and I had heard a lot about mini-splits not dealing well with that so I went with the conventional HVAC and have been happy with it – good air flow and no issues with humidity. Also, visually it looks a lot nicer than having the ductless unit on the wall and this is probably better for resale… since it looks cleaner and more like what people are used to having in their homes.

    We set the air handler at the end of the attic space and ran insulated round, hard air supplies around the outside edge of the attic to maximize storage space and also to maximize filtered air flow from the air handler. Also, with mini-splits, each ductless unit has its own condensate drain line to run outside, so with just one central air handler we only have to worry about one of them getting clogged up over time and spilling over. We installed a pan with a drain tube and pan switch that sends a message to the thermostat to turn off if there is any blockage in the drain tube.

  10. Hi Chris – most split systems (both mini-split and ducted) and window/room AC units have a drain the runs from a drain pan under the cold coil, allowing the condensed water vapor to be discharged outside of your home or into some sort of drain.

    I am not really familiar with portable AC units but if they don’t have a drain or some sort of collection device (like a dehumidifier) then they might be using the moisture to cool the condensing (hot) coil – but this would just re-evaporate the moist air into the living space, thus not doing much for any humidity you have there. If you live in a humid area you might want to research this more.

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