Converting Oval HVAC Ducts to Round: A Complete Guide

Converting Oval Ductwork to Round: What You Need to Know

Oval ductwork has been commonly used for HVAC systems in the past, but many contractors now prefer to use round ductwork instead. Converting existing oval ducts to round offers several benefits that can improve system performance and efficiency.

However, replacing oval ducts with round ducts also requires some important considerations during the conversion process. Here is an overview of the key factors involved in converting oval ductwork to round ductwork in residential or commercial buildings.

Benefits of Converting to Round Ductwork

There are several good reasons to consider changing oval ducts to round ducts in an HVAC system retrofit or renovation:

• Improved airflow The rounded shape promotes smooth, unobstructed airflow compared to oval or rectangular ducts.
• Increased capacity Round ducts can handle higher airflow and velocity than other shapes.
• Less friction The smooth interior surface reduces resistance and turbulence for air handling units.
• Less leakage Round ducts have fewer joints and seams where air can leak compared to oval ducts.
• Higher pressure The smaller surface area decreases static pressure compared to non-round ducts.
• More layout options Round ducts take up less space and can fit in tighter areas.
• Easier cleaning and maintenance It's simpler to access round ducts to clear obstructions and clean interior surfaces.

For these reasons, round ductwork is now the standard for most new HVAC installations. Converting existing oval ducts can help bring older systems up to current standards.

Drawbacks of Converting to Round Ducts

However, there are also some potential downsides to converting oval ducts to round:

• Higher material costs Round ductwork costs more than oval ducts per equivalent CFM rating.
• More planning Good design is crucial to ensure proper sizing and layout of the new round ducts.
• Labor intensive Physically replacing all the ductwork is a major undertaking requiring skilled technicians.
• System downtime The HVAC system may need to be shut off for an extended period during the duct replacement process.
• Drywall and building repairs Walls, ceilings, and other structures may get damaged and require repair from the ductwork changes.

In many cases though, the performance benefits outweigh these drawbacks of an oval to round duct conversion.

Key Steps for Converting Oval to Round Ductwork

If you decide to move ahead with converting oval HVAC ducts to round, here are the key steps involved in the process:

1. Evaluate the Existing Ductwork

The first step is to thoroughly evaluate the current oval ductwork system. Consider factors like:

• Duct sizes and layout
• Branch locations and takeoffs
• Placement of dampers, registers, grilles, and diffusers
• Locations of plenum boxes and tap-ins
• Conditions of any insulation
• Areas of leakage, damage, or corrosion

Documenting all this helps plan the new round duct system.

2. Design the New Round Duct System

Then work on designing the new round duct layout using the existing oval system evaluation. Important design considerations include:

• Selecting optimal duct diameters and materials
• Minimizing length, bends, and fittings
• Maintaining proper slope for drainage
• Accommodating building beams, joists, and obstacles
• Ensuring adequate support and spacing
• Locating access doors and cleaning points

Proper planning minimizes mistakes and rework during duct installation.

3. Select Duct Materials

Choose appropriate ductwork materials like:

• Galvanized steel Durable and economical but requires insulation
• Aluminum Lightweight and corrosion resistant
• Stainless steel Ideal for coastal areas due to corrosion resistance
• Fabricated Pre-insulated, easy to install duct boards or flexible ducts

Consider factors like cost, R-value, longevity, and installation requirements.

4. Size the Ducts Correctly

Proper duct sizing is crucial. A qualified HVAC technician can determine the optimal duct diameters using manual calculations or duct sizing software. Key factors for sizing include:

• CFM ratings of the HVAC equipment
• Total system static pressure
• Length of each duct run
• Desired airflow velocity - usually under 1200 FPM

Oversized ducts can hinder system performance and efficiency.

5. Remove the Old Oval Ducts

With planning and materials ready, its time to remove the old oval ductwork. Technicians will:

• Disconnect and cap old duct sections from the HVAC equipment
• Cut ducts into manageable sections for removal and disposal
• Temporarily cap any open ports
• Protect registers and diffusers not being replaced
• Patch holes and repair surfaces

Proper containment and disposal of old insulation is necessary if it contains asbestos.

6. Install the New Round Ducts

The new ducts can be installed once sections of the old ductwork are removed. This involves steps like:

• Placing and securing duct supports and hangers
• Fitting and sealing straight duct sections and fittings
• Installing any necessary dampers, turning vanes, or access doors
• Connecting ducts to registers, grilles, diffusers, and plenum boxes
• Insulating any unwrapped metal ductwork
• Sealing all joints thoroughly

The goal is an airtight system using quality clamps, seals, and seams.

7. Start Up the System

With the new round ducts installed, the system can be started up. This involves:

• Inspecting work and leak testing
• Reconnecting HVAC equipment
• Powering up air handlers and testing controls
• Balancing airflow to registers and diffusers
• Testing system performance under full load

Tuning and adjustments help ensure optimal airflow and efficiency.

Key Takeaways

Converting existing oval ductwork to a new round duct system provides performance benefits, but also requires careful planning and skilled installation. Key takeaways include:

• Round ductwork improves airflow, reduces leaks, requires less space, and allows for easier maintenance compared to oval ducts.
• Proper duct sizing, layout, and material selection are crucial when changing oval to round ducts.
• The conversion process is labor intensive and requires containing or safely removing old insulation.
• There will likely be costs for increased duct materials, building repairs, system downtime, and labor.
• An HVAC professional can determine if converting oval to round ducts makes sense based on factors like system age, capacity needs, and overall conditions.

With the right approach, oval to round duct conversions can significantly improve the performance of older HVAC systems.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.