What is Cross Leakage in ERV's and Why it Matters Particularly in Multi-Family Projects?

Cross leakage refers to the unintended transfer of air between the exhaust air stream (from inside the building) and the incoming fresh air stream (from outside) within an ERV unit.

Instead of fully separating the stale exhaust air from the fresh intake, a small portion of the air “leaks” across the heat exchanger. This happens due to:

• Pressure imbalances

• Poor internal sealing

• Design characteristics of the ERV core (e.g., plate, enthalpy wheel, polymer membrane)

  
  

🛑 Why is Cross Leakage a Concern?

1. Indoor Air Quality (IAQ):Contaminants like VOCs, humidity, or odors from kitchens/bathrooms can re-enter living spaces.

2. Energy Performance:Cross leakage can falsely boost apparent energy recovery efficiency (because some of the return air is recirculated, not fresh air that was conditioned).

3. Code & Certification Issues:Passive House and other high-performance programs (e.g., PHI, PHIUS) require cross leakage limits — often less than 3%. Some ERVs can't meet this threshold.

   
   

🏢 Cross Leakage in Multifamily Context

Multifamily buildings are especially sensitive to cross leakage due to:

• Shared ERVs: In many designs, a central ERV serves multiple apartments. This raises the risk of cross-contamination between units.

• Sensitive populations: IAQ is critical, especially with elderly residents and children.

  
  

📊 ERV Performance and Cross Leakage

ERVs vary significantly in how well they control cross leakage:

• High-performance units use tightly sealed heat exchangers, keeping leakage below 3%.

• Mid-range systems often have higher leakage, especially if they use enthalpy wheels or less robust internal separation.

• Budget-friendly or older models may see very high cross leakage, making them less suitable for stringent energy or IAQ goals.