The little known check every auditor should be doing in every home.

HVAC guys (hopefully) know the importance of measuring static pressure, but what about energy auditors? All auditors should be measuring static pressure because it tells us how well the air is moving through the ductwork under operating conditions, not under 50 Pa of blower door pressure.  

A high static pressure means there are restrictions on your supply ducts (the ones pushing air out and cooling your home) or that there too many restrictions on the return side (the registers where you change the air filter).  High static pressures are a major cause for early compressor failures.  There is an easy check to see if you have duct registers that are restrictive or not.


A super easy check every auditor can do is to simply check what kind of registers you have on the ceilings and walls. Believe it or not the style of register you have has a huge impact on how effectively your heating and cooling runs.


Restrictive supply registers will cause your air to back flow through the ductwork creating imbalances and overworking the AC unit. A restrictive return grille or register will not bring enough return air into the system (or enough out of the other side), starving the unit of air. 

How often do we find these restrictive registers during our home energy audits? More often than you think, about 8 out of 10 homes have a restrictive return grille and 4 out of 10 homes have stamped face supply registers. 

Stamped faced registers have fixed or semi-fixed grilles that are "stamped" on. The grilles are characterized by smaller openings that are at sharp angles almost parallel to the floor. They not only restrict the airflow out of the the register, but they can't be adjusted to redirect the air. 

High flow registers aka bar type grilles or opposing blade dampeners have fewer grilles, are spaced out less frequently and are sometimes fully adjustable. They let a significantly more amount of air to pass through, making your heating and cooling system work less to keep the home at a comfortable temperature and humidity.

By simply switching your registers you can achieve greater comfort with higher airflow's into and out of the system. Here are some photos of stamped faced registers and bar grilles for reference.

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Comment by David Byrnes on November 30, 2013 at 1:16am
We have always tested out after switching to bar grilles but there was always other work done that affected the static readings. Increasing the size of the return, adding additional returns, putting throw away filters and adding jump ducts will all reduce the static. But ductwork sealing is going to increases the static pressure so our work is always offset a bit. In testing simulators I have seen the static drop by 0.5 Pa from simply opening a register that was shut. Anyone have data from just switching stamped faced registers alone what the static pressure drop was?
Comment by Mike Fredricks on October 8, 2013 at 11:17pm

Heating and cooling system: Learning about the energy effectiveness of your heating and cooling system is essential. If this is not checked there could be an plentiful amount of power being lost that you do not even recognize. http://ledchoice.eu/

Comment by Steve Waclo on September 26, 2013 at 12:52am
Hello David,

Thanks for making time to post this information.

You have discussed the effect of restrictive "stamped" registers and return grills in qualitative terms and it would be much appreciated if you could put some numbers with your assertions.

Any case studies?

Standing by!

Best wishes.

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