What is low profile ductwork?

Low profile ductwork, also known as flat oval ductwork, is a type of HVAC (heating, ventilation and air conditioning) ductwork that has a lower vertical profile compared to traditional round ductwork. As the name suggests, low profile ductwork has an oval or rectangular shape rather than the standard circular ducts. This shape allows the ducts to fit into tighter spaces with restricted heights, like attics or crawl spaces.

What are the benefits of low profile ductwork?

Some key benefits of using low profile ductwork include:

• Fits into tight spaces – The flattened oval or rectangular shape can squeeze into constrained spaces only 5-6 inches in height. Round ductwork requires at least the duct diameter vertical clearance.
• Increased airflow – The elongated oval shape actually increases airflow compared to round ducts of the same cross-sectional area. This improves HVAC performance.
• Easier installation – Low profile ducts install faster with fewer fittings needed to route around obstructions in cramped areas.
• Better airflow control – The flat shape reduces air turbulence and resistance, allowing smoother, more efficient airflow.
• Aesthetics – The ductwork hugs the framing and takes up less visible space in the living area.
• Versatility – Low profile ductwork comes in a range of sizes to accommodate different airflow requirements.

What are the downsides of low profile ducts?

There are a few potential disadvantages to consider with low profile ductwork:

• Increased risk of kinks – The flattened shape is more prone to kinking at bends, which constricts airflow.
• Increased noise – The turbulent airflow in certain low profile duct configurations can generate more noise.
• Higher cost – Low profile ductwork costs 15-20% more than round ductwork per linear foot.
• Limited sizes – Size offerings are narrower than the extensive options for round ducts.
• Improper installation – If installed compressed or bent too tightly, the ductwork loses performance and capacity.

When should you use low profile ducts?

Here are the situations where low profile ductwork is the best choice:

• Attic with height restrictions – Low profile ducts work well when passing through truss framing or joists in tight attic spaces.
• Underfloor installation – The shallow ducts fit beneath floors or crawl spaces with minimal clearance.
• Renovation projects – Allow retrofitting ductwork into existing spaces not originally designed for HVAC.
• Basements with low ceilings – Low clearances make standard round ductwork unfeasible.
• Alteration of existing ducts – Oval shapes can replace or supplement undersized or leaky existing ductwork.

Low profile ducts are also commonly used in multi-family dwellings like apartments where space is at a premium.

What sizes are available?

Low profile ductwork comes in a range of dimensions to suit different airflow requirements:

Duct Size	Dimensions (inches)	CFM Range*
10×4	9.75 x 3.75	70-90
10×6	9.75 x 5.75	90-120
12×6	11.75 x 5.75	110-150
14×6	13.75 x 5.75	140-190
16×8	15.75 x 7.75	220-300
18×8	17.75 x 7.75	260-375
20×8	19.75 x 7.75	300-425
20×10	19.75 x 9.75	350-500

*CFM range is approximate for a given duct size and depends on factors like length and number of bends. A HVAC load calculation is required to properly size ductwork.

The dimensions represent the flat widths of the oval duct. Actual duct heights are 1-2 inches shorter due to crimping. Low profile duct sizes often transition to larger round ducts for main trunk lines.

How should low profile ducts be installed?

Proper installation techniques are critical for low profile ducts to perform correctly:

• Meticulous planning – The routing layout should minimize sharp bends and compression.
• Careful spacing – Ducts must be spaced 1 inch or more off framing with no compression.
• Gradual bends – Use large radius elbows where possible, and avoid kinking ducts.
• Limit compression – Do not flatten or crush ducts on top or bottom.
• Secure braces – Use braces to hold shape on long straight runs.
• Seal joints – All transverse and longitudinal joints must be tightly sealed.
• Insulation – Insulate ducts to prevent condensation and maintain air temperature.

Poor installation with tight bends or compression can reduce airflow by up to 30% compared to properly installed ducts.

What materials are used?

Low profile ductwork is constructed from rigid metals like:

• Galvanized steel – The most common material is galvanized steel sheet metal coated with zinc to resist corrosion. Minimum thickness is 28 gauge.
• Aluminum – Aluminum is lighter than steel but more prone to denting. It has better corrosion resistance than galvanized steel.
• Stainless steel – The most durable option with excellent corrosion resistance, but also the most expensive.

Spiral wire reinforcement is sometimes added for long straight duct sections to prevent buckling. Aluminum or stainless steel are used for coastal areas or corrosive conditions.

How is low profile ductwork installed?

The typical installation process involves these steps:

1. Layout the duct plan and required sizes based on load calculations.
2. Cut flat sheet metal to required duct dimensions using sheet metal shears.
3. Use a crimper tool to crimp one side of the duct to form the oval shape.
4. Connect duct sections together using either snaplock seals or duct sealant.
5. Use sleeve joints to attach round supply collars or registers to the flat ducts.
6. Install duct hangers to properly space and support ducts off framing.
7. Seal all joints thoroughly with duct sealant or aluminum foil tape.
8. Insulate the ducts to required R-value based on climate zone.

The ducts are crimped to around 1-2 inches shorter than the flat dimensions to form the oval shape. All sharp bends should be avoided.

How much does low profile ductwork cost?

Like most HVAC work, the total cost of low profile ductwork depends on several factors:

• Ductwork cost per linear foot – The duct material chosen affects cost per foot. Galvanized steel is the most economical, while stainless steel costs substantially more.
• Number of duct fittings – Elbows, transitions, registers, hangers and other fittings add cost.
• Insulation – Adding insulation increases total cost but is required by code in most areas.
• Labor rates – HVAC installer labor rates vary across regions from around $50 – $100 per hour.
• Access challenges – Difficult attic or crawl space access can slow down installation and increase cost.

As a rough estimate, a typical 2000 sf home might use around 200 linear feet of low profile ductwork costing $8-$12 per foot for materials plus $2000-$4000 for labor. Total installed cost would likely fall in the range of $6000 to $10,000 or more.

What are the alternatives to low profile ducts?

The main alternatives to low profile ductwork include:

• Round metal ducts – Standard galvanized steel or aluminum round ducts. Less costly but require more space.
• Flexible ducts – Constructed from wire helixes covered in insulation. Used for final branch runs and connections.
• Rectangular ducts – All-metal rectangular ducts that also have a low profile shape but different proportions.
• Duct board – Ducts constructed from rigid fiberglass boards with foil facing. Used for trunk and branch runs.

Each duct type has pros and cons and is suited for different applications. Oval low profile ducts offer a nice compromise of compact footprint, performance, and affordability.

Conclusion

Low profile ductwork provides a versatile and cost-effective solution for installing HVAC systems in tight spaces with low ceilings or headroom. The compact shape saves room compared to bulky round ducts, while still providing quiet, efficient airflow. With good planning and careful installation focused on gradual bends and no compression, low profile ducts offer an optimal way to route heating and cooling airflows through confined areas. If space constraints exist, be sure to consider low profile ducts during your next HVAC project.