I'm going to venture to say that at least 80% of the homeowners out there have experienced this annoyance where certain rooms of the home are colder in the winter and warmer in the summer as opposed to the rest of the house. This can be a nuisance and in extreme circumstances, a major comfort problem. If you have experienced this and you have called a professional out to analyze the issue, you likely got told to leave doors open, adjust vents, use a different filter, a whole slew of things that didn't really seem to fix the issue. The solution is the one thing that all these suggestions have in common and that is to deliver the appropriate amount of air (heat/cooling) to the space.
Central air system deliver heat and/or remove heat via the air that circulates through the home. The highway that facilitates this air movement is the duct system. I used to think that duct systems where easy to design as I've seen many company owners assign the size of ducts for a space based on the size. What I mean is they would say if a room is 10x10 or somewhere close to that, it gets a 6 inch run. I literally had one "industry professional" tell me that all bathrooms get 4 inch, large master baths get 2- 4 inch runs, bedrooms less than 140 sq feet get a single 6 inch run, large living spaces such as the living room get 8 inch runs. I now know how flawed this line of thinking is and this is also the reason you have uneven heated and cooled homes.
Properly designed duct systems that follow the ACCA Manual D process deliver the exact amount of air to a space so that it doesn't over or undershoot the desired temp by more than 1 or maybe 2 degrees. That's a very tight scale to deliver and most people wouldn't notice the difference between 71 and 72 degrees, but that's the goal. The solution is properly designed AND installed duct systems. The last act to truly maximize comfort in this regards to install balancing dampers in the ducts that go to each vent so you have the ability to balance the duct system. Balancing refers to a process where we take an accurate load calculation with the designed cfm for each space along with a flow hood, and we adjust all the balancing dampers to get the airflow as close as possible to the actual design. This process is mandated in commercial applications as very large systems can be grossly out of balance due mainly to the amount of airflow that a single system handles. I've had to do this in one very large home in Wilmington, NC that had a 5 ton unit but it was not delivering the necessary airflow to some of the areas. I've done this as a courtesy for some of my installs out of anticipation that if I didn't, it would be an issue later.
If you are experiencing this issue in your home, you will need an accurate load calculation performed, a friction rate calculation of the existing duct system, as well as a modified manual D (likely with balancing dampers), to ensure the proper distribution of air to each space.
Kenneth Casebier
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