Filter Grill Requirements Update from the CEC

While testing at BECT.us I have come across a number of air conditioning systems that do not meet the total airflow and fan/watt draw levels of performance that the code calls for. When this happen the HVAC contractor has to redo the return duct design and then install it at significant cost of time and reputation. It shows that the system was never actually designed but pieced together using a best guess. There has got to be a better way.

The CEC has just sent out an update of their filter grill requirements which are a critical part of the return duct system. Here is there update.

"Filter Grille Area Requirements

When complying with the Alternative to Section 150.0(m)13B, the nominal size of the air filter media should be used to calculate the minimum total return filter grille gross area. If the air filter is not located at the filter grille, use the nominal size of the filter grille to determine the area. The calculated area must be equal to or greater than the values in TABLES 150.0-C or D.

Additionally, TABLES 150.0-C and D also require that:

 1. Each return duct must be no longer than 30 feet.

2. Each return duct must not have more than 180 degrees of total bend.

3. If the total bending of a return duct is more than 90 degrees, one bend must be a metal elbow.

4. Return grille devices, which include the air filter and return grille locations, must be labeled in accordance with the requirements of Section 150.0(m)12A.

 5. The label must state the grille’s design airflow rate and a maximum allowable clean-filter pressure drop of 12.5 Pa (0.05 inches water) for the air filter, as rated in accordance with AHRI Standard 680 for the design airflow rate for the return grille. Please note that additional air filtration requirements of Section 150.0(m)12 may apply."

I've seen some contractors who were shocked at how much filter area the code was calling for. Of course, the best way to make sure that the filter grill requirements are met is to use a proper duct design system such as Right Soft. The vast majority of installations that I see are not designed at all.

I hope that bringing this to light could alleviate some of the pain I've seen in the eyes of someone who has to redo their hard work often in a sweltering attic.