A mini-split system, also known as a ductless mini-split system, is a type of air conditioning and heating system that allows you to control the temperature in individual rooms or zones in a building. Mini-split systems are composed of an outdoor compressor/condenser unit and one or more indoor air-handling units, connected by pipes and wires. The indoor units are mounted high on interior walls or ceilings.
Ductwork is typically used in traditional, centralized HVAC systems to distribute conditioned air throughout a building. Ducts transport air from a central air handler to vents located in different areas. Mini-split systems provide an alternative to ductwork by delivering heating and cooling directly to the space, without ducts.
So can you connect ductwork to a mini-split system? The short answer is yes, mini-split systems can be ducted, but there are some important considerations to keep in mind. Ducting a mini-split system can help improve airflow and temperature balance in a space, but improper design or installation can reduce efficiency and performance.
In this article, we’ll take a deeper look at ducting mini-split systems, including:
- How ducted mini-splits work
- Key benefits of ducting a mini-split
- Potential drawbacks to be aware of
- Tips for design and installation
- Example ducted mini-split configurations
- Costs of ducting a mini-split
Understanding these key points will help you determine if connecting ductwork to your mini-split system makes sense for your specific needs and application.
Page Contents
How Ducted Mini-Split Systems Work
Mini-split systems are designed to be flexible in installation and can operate with or without ductwork. Here is an overview of how ducted mini-splits function:
– The outdoor unit and indoor unit(s) operate the same as a standard ductless mini-split system. The outdoor condenser compresses refrigerant into a hot gas that is pumped to the indoor unit(s).
– The indoor unit houses the evaporator coil that absorbs heat from the air and converts the refrigerant back into a liquid.
– A fan in the indoor unit blows air over the evaporator coil and then circulates the now cooled air directly into the rooms.
– With a ducted mini-split, you connect ductwork from the indoor unit’s supply and return air vents to additional supply registers and return grilles installed in other areas.
– Conditioned air is pushed through the ductwork into separate zones you want to heat or cool.
– The indoor unit’s fan must be sized and powered appropriately to overcome the static pressure resistance from pushing air through the ductwork.
– Zoning dampers or balancing dampers may be used to control airflow and better regulate temperatures in different duct runs.
– A thermostat is located in each zone to activate the system and control temperature.
So in essence, the ductwork acts as an extension of the indoor unit to deliver heating or cooling to multiple rooms, rather than just the single space where the indoor unit is mounted. The condensing and evaporator functions happen in the mini-split components, while the ductwork serves as the air distribution system.
Benefits of Ducting a Mini-Split
There are several potential advantages to connecting ductwork to a mini-split system:
Improved Air Distribution
Ducts allow conditioned air to be directed to different areas more effectively compared to unducted air discharge from a wall or ceiling mount. Rooms farther from the indoor unit can receive stronger airflow. Ducts also let you route air around obstacles and where you want outlets located.
Balanced Temperatures
Ductwork helps minimize hot and cold spots by spreading the heating and cooling more evenly. Without ducts, farther zones tend to be warmer or cooler.
Zoned Comfort Control
Ducted systems allow you to set different temperatures in each zone. The registers in frequently occupied rooms can be opened wider to maintain comfort.
Flexible Installation
Ducts make installation easier in homes with finished walls and ceilings where you don’t want wall units visible. The indoor unit can mount in a closet, attic space, crawl space, or basement while ducts route air elsewhere.
Quieter Operation
With wall-mounted units, the fan noise enters directly into the room. Ducts allow the indoor unit to be located away from living areas for quieter ambiance.
Preserves Space
Since air handlers mount out of sight, they preserve more useable wall and ceiling space compared to multiple visible wall units.
Aesthetic Appeal
For many, ducted systems provide a more polished, integrated look compared to wall units. Registers blend in like a forced air system.
Flexible Sizing
Mini-splits are offered in a wide range of indoor unit sizes. A properly sized large unit can support several smaller ducted zones.
Potential Drawbacks to Ducting Mini-Splits
While ducting a mini-split can provide benefits, there are also some downsides to consider:
Higher Upfront Cost
Ductwork, registers, grilles and labor will add cost compared to a basic ductless setup. Installation also takes more time.
Increased Complexity
Ducted systems require more design consideration and precise installation to function correctly. Improper duct sizing, layout or leaky joints can degrade performance.
Airflow Imbalances
Despite dampers, some rooms may get more airflow than others. Distant or restrictive duct runs create imbalances.
Reduced Efficiency
The static pressure drop through ductwork causes the indoor unit fan to work harder, increasing energy consumption.
Condensation Issues
Cold conditioned air moving through hot unconditioned spaces can accumulate condensation on duct surfaces. Insulation helps mitigate this issue.
Space Constraints
Ducted systems need adequate room for indoor units, duct runs, and accessible installation areas above ceilings or in attics.
Maintenance Access
Ducted systems require accessible indoor units for filter changes, repairs and maintenance.
Design and Installation Considerations
Careful planning in the design and execution of the ducted system helps maximize performance and avoid problems:
Undersize Indoor Unit
Choose an indoor unit at least one size smaller than the total capacity all zones will require. Oversizing the unit leads to short cycling and humidity control issues.
Manual J Load Calculation
Performing an accurate heating and cooling load calculation for each zone using ACCA Manual J guidelines is important for proper duct and equipment sizing.
Right-sized Ductwork
Ducts must be sized correctly to handle the proper cubic feet per minute (CFM) of airflow to each zone based on calculations. Oversized ducts can hinder velocity.
Minimize Duct Length
The shorter the duct runs, the lower the static pressure losses. Try to locate the indoor unit centrally. Limit the longest run to 25 feet or less.
Proper Duct Materials
Use smooth metal ductwork, not flex duct, for reduced friction resistance. Insulate ducts to prevent condensation and energy losses.
Sealing Ducts
All duct joints must be thoroughly sealed with mastic to prevent leaks that reduce airflow and efficiency. Use quality dampers.
Return Air Ducted
Conditioned zones should have dedicated return ducts leading back to the indoor unit to maintain proper airflow balance.
Room-by-Room Control
Install individual smart thermostats in each zone to control temperatures based on occupancy and usage patterns.
Commissioning System
Have an HVAC technician confirm proper airflow, the refrigerant charge, and system operation after installation.
Example Ducted Mini-Split Configurations
Here are two common ways ducted mini-split systems are configured:
Single Indoor Unit, Multiple Zones
This setup has one larger capacity indoor unit located in a central area like a closet or attic. Ductwork distributes air from the unit to multiple zones (rooms) in the building. The cfm delivered to each zone is controlled by adjusting the individual supply registers. Return ducts bring air back to the indoor unit. Each zone has its own thermostat.
| Indoor Unit Location | Zone 1 | Zone 2 | Zone 3 |
|---|---|---|---|
| Central Closet | Bedroom | Living Room | Kitchen |
Multiple Indoor Units, Multiple Zones
This type uses several smaller indoor units located in different areas of the building. For example, one unit could be in an attic and one unit in a basement. Ductwork from each indoor unit supplies air to the zones in that general vicinity. The units operate independently to serve different zones, while the outdoor condenser is shared.
| Indoor Unit 1 Location | Indoor Unit 2 Location | Zone 1 | Zone 2 | Zone 3 |
|---|---|---|---|---|
| Attic | Basement | Bedroom | Living Room | Kitchen |
This configuration allows good balance between the zones attached to each air handler. It also provides redundancy if one unit needs repair. The downside is higher equipment cost with multiple indoor units.
Cost of Ducting a Mini-Split
Ducting a mini-split system does add cost over a basic ductless setup. Equipment and installation costs include:
– Larger indoor unit: $500 to $1000 more
– Ductwork materials: $1000 to $2000
– Registers/diffusers: $200 to $500
– Additional installation labor: $1000 to $2000
So ducting a mini-split can add $3000 to $5000 total to the cost of the system. However, remember you are gaining year-round heating and cooling for an entire home compared to just a single room. The boosted performance, comfort and resale value helps offset the higher initial investment.
Conclusion
Ducting a mini-split system allows you to enjoy the benefits of zone control and energy efficiency these systems provide, while also distributing conditioned air through an entire building. Ductwork helps send heating and cooling to rooms farther from the indoor unit(s) and improves temperature balance compared to non-ducted units.
With proper load calculations, design, duct sizing, and professional installation, a ducted mini-split can provide superior comfort with minimal drawbacks. The increased initial cost over a basic ductless system is usually returned through greater comfort, lower energy bills, and added home value. Just be sure your HVAC contractor carefully plans the ducted design and airflow requirements.