Return ducts code requirements have changed

Return DuctMichigan Law requires changes to the energy code must have a payback within a certain period of time.  The new 2015 Michigan Residential Code that was implemented on February 8, 2016 had a requirement that return ducts needed to be ducted and no longer allowed builders to use the wall cavities as a duct.  The State of Michigan was challenged, stating that this requirement does not have a payback within the time frame required by law.  The State has amended that requirement and now allows builders to use the old way of ducting the returns.

Do you agree with this change?

I am conflicted.  On one hand, I agree that the payback is probably a long time by using actual duct material to make the returns.  On the other hand the duct distribution design is extremely important.  I understand that requirement complicates the design and ultimately increases the cost to the builder and the home buyer.  I do think the mechanical inspectors need to be more stringent on making sure these cavities are sealed as best as they can and cleaned out as best as they can.  If a wall cavity is sealed properly it will most likely function just fine.

I think our energy is better spent on really designing the duct work around the specific house it is going in.  Manuel J, S and D calculations are extremely important.  If your HVAC contractor is not doing these calculations or not at least contracting them out, find a new contractor.  Its like your carpenter not using a tape measure.  The more complicated the design of home, the more important these calculations are.


Even though the State has amended the requirement to duct the returns, make sure you check with your local building inspector on what they are requiring.  We have received word that some building inspectors are still going to require this.  You mine as well check up front and save a huge mess down the road.

For more information on this change go CLICK HERE.

Here is the wording from the LARA website.

The Michigan Residential Code (MRC) Sections N1103.2.3 and M1601.1.1 conflict regarding the use of building framing cavities for plenums. The conflict is resolved in favor of M1601.1.1 as MRC Section M1601 is the definitive section on duct construction. This decision is based on MRC Section R102.1 (Where there is a conflict between a general requirement and a specific requirement, the specific requirement shall be applicable.) and that Section N1103.2.3 has not been shown to meet the definition of cost effective.

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