Replacing an HVAC rooftop unit (RTU) often requires a curb adapter to ensure the new unit fits the existing curb. Accurate measurements are critical to avoid installation delays, costly errors, and performance issues. In this guide, we’ll walk you through the process of measuring both the existing curb and the new unit for a perfect fit.
Why Accurate Measurements Matter
Roof curb adapters bridge the gap between the new RTU and the existing roof curb, allowing for seamless installation without requiring costly modifications to the roof structure. Incorrect measurements can result in poor airflow, leaks, and additional expenses. By following these steps, you’ll ensure that your curb adapter fits perfectly.
Step 1: Gather Key Information
Before heading to the roof, determine the following:
- Is the RTU installed on the original curb that is roofed into the building, or is it already on a curb adapter?
- If the RTU model number or manufacturer’s information is visible, take note of it. You can now order online using our Curb Adapter Portal. (Learn how to use our curb adapter portal)
- Take photos of the RTU, roof curb, and surrounding area to document key details like gas lines, electrical conduits, and obstructions.
Step 2: Measure the Existing Roof Curb
Outside Perimeter
- Measure the long and short dimensions of the original roof curb from the top flange.
- Do not measure the unit’s base rail or an existing curb adapter. Focus on the roof curb that is directly attached to the building.
- Avoid adding any dimensions—curb adapter designs will account for necessary adjustments.
Supply and Return Openings
- Measure the supply and return duct openings at the top of the roof curb.
- Record the distance between the roof curb’s outside edge and each opening to ensure proper alignment.
For more tips on HVAC system measurement, check out this guide from Buildings.com.
Step 3: Check for Level
Use a level to determine if the existing roof curb is sloping. If it is, document the direction and degree of the slope. Many curb adapters can correct minor leveling issues, but this must be addressed during design.
For additional resources on leveling and structural integrity, visit ASHRAE.
Step 4: Identify Obstructions
Measure and document the distance between the existing curb and any obstructions, such as:
- Nearby HVAC units.
- Exhaust fans or vents.
- Gas piping or electrical conduits.
- Walls or roof edges.
These details ensure that the curb adapter design accommodates tight spaces or tricky layouts. Learn more about managing rooftop equipment from FacilitiesNet.
Step 5: Measure the New HVAC Unit
If the RTU model number is unavailable, manually measure the following:
- Base Rail Dimensions: Measure the long and short sides of the new unit’s base rail.
- Duct Openings: Measure the supply and return openings on the unit to ensure proper alignment with the curb adapter.
Step 6: Avoid Common Mistakes
Don’t Stack Adapters
- Never install a roof curb adapter on top of an existing adapter. This creates structural issues and increases static pressure, reducing system performance.
Don’t Measure the Unit Instead of the Curb
- Measure the original roof curb, not the RTU base rail or unit pan openings. This avoids discrepancies caused by variations in unit sizes.
For a deeper dive into HVAC best practices, explore resources at HVAC School.
Step 7: Use a Field Verification Form
At Madon Sheet Metal, we provide a Field Verification Form to help you capture all necessary measurements accurately. This form simplifies the process and ensures you don’t miss any critical details.
Get Expert Help
If you’re unsure about any step in the measurement process, our team at Madon Sheet Metal is here to help. With decades of experience in custom curb adapter fabrication, we’ll ensure your project runs smoothly.
📞 Call us at (224) 300-7995
🌐 Visit us at madonsheetmetal.com
🔗 Request a Quote
By following these steps and avoiding common pitfalls, you can ensure your curb adapter is designed and fabricated to fit perfectly, saving you time, money, and headaches. Let Madon Sheet Metal help you get the job done right the first time.