TOPIC: Because The J Sheet Says So

It was another new construction inspection, and another call from another supervisor.

"How did you figure out the air flow from the heat registers?"

On new construction I ALWAYS check the airflow from HVAC registers.  I do that because sometimes they systems are not balanced well, or connected properly or the ducts (glorified slinkies) are wrapped so tightly around rafters that they are crushed and don't blow air.  I should feel a strong air flow from each.  A good amount of air is between 400 and 600 cubic feet per minute.

"I use a meter, why?" (You see it below)

"We think the airflow is fine because the J sheet says so."

This house has two systems.  The upper level system was found to provide 550CFM or better to one half of the house and 177CFM or less to the other half.  One register blew 63CFM.  That is a balance problem.  That system either lacks a damper or has one that is not adjusted properly.  In fact, one register in the master bedroom blew 589CFM and the other 149!

"What is the J sheet?"

"That's what the HVAC guy uses to pick out the duct sizes and how much air they blow out.  And some of what you wrote down is more air than the J sheet calls for.  And the County already approved it."

They always bring in the County to try to bolster their case.

"You mean the County and the J sheet want half the master bedroom to blow air at 1/4 the rate of the other half?"

I heard crickets on the line, hard to do when you are driving.

"I don't care what the County says.  Do you think I think they actually check the CFM rates?  And I don't care what the J sheet says.  It clearly doesn't say that half the upper level should blow air really well and the other half not.  That's a balance problem.  Don't you agree?"

He had no come back.  "You should have it checked out.  You would if it was your home."  End of conversation.

My recommendation:  Especially on new construction, but even if you are buying or selling an older home, walk around and feel the air blow from the registers.  It should be a strong blow.  If not, note it and have it checked out.  You will appreciate that in January and July.

Totally agree Jay. Good job!

Got to love the excuses.

"What is the J sheet?"

"That's what the HVAC guy uses to pick out the duct sizes and how much air they blow out.  And some of what you wrote down is more air than the J sheet calls for.  And the County already approved it."

Jay:
Great comments.
From my experience in commercial construction, I am familiar with the engineers design documents indicating the CFM on each diffuser and the required balance report the balancing contractor is required to submit certifying the initial and final readings. Sounds like this is a similar requirement in residential construction in your area?
Not done very often up here in the sticks!!! Must be a factor of how long the arm of governmental regulations is!!!
By the way, what does the "J" stand for?

(Not sure if I did the partial quote correctly. Guess I will find out when it shows up.)

I don't know what the J is for Gary.  Maybe intended to slam me?  I had never heard of it before.

The code is the code, but I doubt they have a CFM requirement.  The house should be balanced though!

Jay;
I certainly wasn't trying to slam you!!!
I am just trying to educate myself.
Looking through chapter 16 Duct Systems of the IRC, I find a reference to designing ductwork according to ACCA Manual D,n whatever that is but maybe that has some requirement for air flows, distribution and balancing which I agree are very important to creating a comfortable environment and efficient system.
Don't have time to look further, got to head to an inspection. First of 4 this week!!!! Business seems to be picking up for this semi-retired, part time newbie!
Keep the posts coming Jay, they always have some great information.