EzERV Ventilation Air Calculator / Design Tool by BTF

ERV Units (Energy Recovery Ventilators): Energy recovery ventilators (ERVs) improve indoor air quality by exchanging stale indoor air with fresh outdoor air while recovering energy from the exhaust air. They transfer both heat and moisture, making them ideal for maintaining humidity levels and reducing energy costs in various climates. 

ERU Units (Energy Recovery Units): Energy recovery units (ERUs) refer more broadly to any system that recovers energy from exhaust air to precondition incoming air, but not moisture. Proper installation is crucial for maximizing the energy recovery and efficiency of these systems. 

Regular maintenance for all HVAC equipment ensures optimal performance and extends the system’s lifespan. 

MERV Filters: MERV, Minimum efficiency reporting value filters capture airborne particles, improving indoor air quality. Regularly replacing these filters is essential for maintaining system efficiency and air quality.

ERV/ERU maintenance: Regular maintenance  includes cleaning or replacing air filters, inspecting the heat exchange core, and ensuring unobstructed fans and vents. This maintenance is vital for consistent energy recovery and ventilation performance.

Balance dampers regulate and control airflow within ducts, ensuring the correct amount of air reaches each room. This improves indoor air quality, enhances energy efficiency, and maintains comfortable living conditions. Properly installed balance dampers reduce noise and prevent over-ventilation or under-ventilation in specific areas.

Even a properly sized & designed system, won't operate well unless it is balanced correctly.

Balanced mechanical ventilation systems provide equal amounts of fresh air supply and exhaust air removal, maintaining consistent indoor air quality and pressure levels. These systems are often more energy-efficient and can be integrated with smart home technologies for enhanced control.

Exhaust-only ventilation systems remove stale air without providing direct fresh air, relying on passive infiltration for fresh air intake, leading to imbalanced pressure and less controlled air exchange. These exhaust-only units may be described as point source exhaust air units.

Ideal design practices for residential ventilation air include the use of a balanced ventilation system with point source exhaust air fans/hoods.

Common Point Source Exhaust Air Sources: Kitchen hoods improve IAQ by removing cooking odors, grease, smoke, and moisture. Proper installation and ventilation of kitchen hoods are essential for reducing airborne contaminants and maintaining a healthy indoor environment. Bathroom exhaust fans control moisture and humidity, preventing mold growth and moisture damage. Selecting a fan with adequate airflow capacity and ensuring it vents to the outside is crucial for effectiveness.

 Natural ventilation involved opening windows and doors to allow fresh air to flow in and stale air to escape. This method is simple but relies heavily on outdoor conditions, which can be unpredictable and seasonal. It also relied on infiltration. 

Infiltration is the process by which outdoor air enters through cracks and gaps in the building envelope. While providing some ventilation, infiltration also leads to energy loss and uneven air quality. The cleanliness of natural ventilation via infiltration is also questionable, being the air that enters must pass through each material of your building assembly, such as old insulation, dirty sheetrock or aging siding.

Infiltration is also being reduced year over year as we build tighter & tighter homes. Builders & building codes ensure proper sealing today, reducing & managing infiltration, effectively reducing this old ventilation method. 

High-end Units: Advanced ventilation units feature energy recovery, HEPA filters, humidity sensors, and smart home integration. These units provide superior indoor air quality, energy efficiency, and user convenience.

Simple Units: Basic ventilation units with a fan and simple controls offer cost-effective solutions for adequate ventilation. These units are easy to install and maintain but may lack advanced features found in high-end models. 

BTF provides designs based on simple units.

Use radius elbows with a radius at least 1.5 times the diameter of the duct. This reduces airflow resistance and turbulence, improving efficiency and reducing noise. Example: For a 10-inch duct, the elbow radius should be at least 15 inches.

Avoid 90-Degree Turns: Use smooth, wide-radius elbows instead of sharp, right-angle turns to minimize airflow resistance and noise. Whenever possible, avoid using 90-degree elbows. Opt for two 45-degree elbows or a wide-radius elbow to create a smoother path for air.

Calculate Proper Size Ductwork: Undersized ducts increase air velocity, leading to noise, pressure imbalances, and higher energy consumption. Oversized ducts can result in low air velocity, reducing system efficiency, causing poor air distribution and insufficient ventilation.

Balance Dampers: Install balance dampers near the supply diffusers or grilles to allow fine-tuning of airflow to each room. Ensure dampers are easily accessible for adjustments during system balancing and maintenance.

Boots/Takeoffs: Use 45-degree takeoffs instead of 90-degree ones to reduce turbulence and maintain airflow efficiency. Seal all boots properly to prevent air leaks and maintain system efficiency. When straight takeoffs are necessary, use turning vanes to guide airflow smoothly.

Layout: Design the duct layout with the shortest and most direct runs possible to minimize friction losses and maintain airflow efficiency. Place HVAC units centrally to assist with short and equal duct runs.

Flex Duct: Flexible in tight spaces and around obstacles. has shorter life span, and larger potential for kinks, cuts and issues. Less durable and more prone to damage than hard ducts. may have higher air friction/resistance and lower airflow efficiency compared to hard ducts. Can be noisier if not installed properly.

Hard Duct: Recommended. Offers better airflow efficiency with less resistance. Quieter operation due to solid construction. Easier to clean, balance, more durable and longer-lasting.

Square Duct: Square ducts can handle high air volumes but may cause turbulence and noise. They are more expensive and difficult to install but are often used in commercial applications where space constraints are a concern.

Round Duct: Round ducts provide smoother airflow with less resistance, reducing noise and increasing efficiency. They are generally more cost-effective and easier to install, making them a preferred choice for residential applications.

Some simple rules of thumb you can use for converting round & square duct on the fly:

4" ROUND  = 3x5, 4x4  

6" ROUND  = 3x10, 4x8, 5x6, 6x6  

8" ROUND  = 4x14, 5x12, 6x9, 7x8, 8x8  

10" ROUND = 5x18, 6x14, 7x12, 8x10,  9x9, 10x8, 10x10

Insulated ductwork helps to maintain the desired temperature of the air being transported, reducing energy loss and improving HVAC system efficiency. Insulation helps to prevent condensation on the duct surfaces, and can help to dampen noise.

Duct Insulation: Insulate ducts running through unconditioned spaces to prevent energy loss and maintain the desired temperature of the air.

External Insulation: Applied to the outside of the ductwork, typically using materials like fiberglass or foam boards.

Internal Insulation: AKA lined ducts, apply insulation to the inside of the ductwork, often using fiberglass lining.

R-Value: Use insulation with an appropriate R-value for the climate and building design.

Even Airflow Distribution: Design the duct system to ensure even distribution of air throughout the building, preventing hot and cold spots.

Balancing: Use dampers and adjustable grilles to balance the system and ensure consistent airflow to all areas.

Measure and Adjust: Measure static pressure throughout the system and adjust dampers to maintain optimal pressure levels, ensuring efficient operation of the HVAC system.

Duct Sealing: Seal all duct joints, seams, and connections with mastic or UL 181-rated duct tape to prevent air leaks and improve efficiency.

Airtight Connections: Ensure all connections are airtight to prevent loss of conditioned air and maintain system performance.

Flow Hood: Use a flow hood to measure airflow at each diffuser or grille to ensure the system meets design specifications.

Adjustments: Make necessary adjustments to dampers and grilles based on airflow measurements.

Duct Blower Test: Conduct a duct blower test to identify and seal leaks, ensuring the system is airtight and efficient.

Balancing Report: Provide a final balancing report to document airflow rates and pressure measurements for future reference.