What is an 'Existing System Evaluation'?

I wanted write a bit about the purpose of this service, "Existing System Evaluations". The price tag may a bit of a shocker to some, and many may not know what it is at all. So, I thought it could be beneficial to say some things about it.

Throughout my time as an HVAC technician I've run into many situations where customers were having issues with an uneven distribution of air in their home. I would get many complaints such as, "this one room is always hot or this side of the house is always cold, etc." Sometimes the fix is easy, sometimes not so much. Unfortunately, when their system was originally installed the ductwork was designed poorly. More than likely, the AC contractor just guessed at it...."eh, we'll run a 6" over here, and 8" over here. That oughta work". And they do this probably based on some rule of thumb like 1 CFM per square foot...and they got a little table that probably looks something like this:

Field duct sizing chart
Flexible Duct
Duct size	Design Airflow
5"	50
6"	75
7"	110
8"	160
9"	225
10"	300
12"	480
14"	700
16"	1000
18"	1300
20"	1700

 Now, I'm not making fun and I'm not saying I've never done it before. Sometimes in a pinch you can get away with this shooting from the hip approach. But in more complex situations, it simply won't do the job. It's an over simplification. It fails to take into account many variables that can impact a. the amount of airflow, and b. the heat load. A 5" duct may on average deliver approximately 50 CFM of air, but that depends of the length of the duct and the static pressure of air at the duct take off. Also, one 150 sq. ft room that has no windows or exterior walls in a home that has R-30 spray foam insulation has a much different heat load than another room of the same size with a big single pane window on the south facing side of a house built in the 1940s...obviously... You also have to look at the system as a whole. If you add a duct to an existing system, it's going to steal air from somewhere else. What impact is that going to have? There are many other considerations that have to be made when designing a new ductwork installation or modifying an existing one.

With that being said, I've found that this air balance issue rears its ugly little head in two main scenarios. These are situations that I've learned to practice caution. And it often requires a very frank conversation between the AC contractor and the home owner. One scenario is one I've already touched on. A service call where-in the customers wants the technician to try to fix an uneven air distribution problem by making a system alteration. The other scenario is where we do an 'equipment change-out'. This means we replace the outdoor and indoor units, maybe run a new line set, but utilize the existing duct work.

In the service call situation there are two options. Option 1: shoot from the hip and hope for the best. In simple situations, this option may work. Buuuuut...and it's a big but... this may waste my time and your money. So, I'm always going to try to let the customer understand up front that there are no guarantees here. To really do it right, you have to do option #2. Thusly, enter the reason for the 'existing system evaluation' service. We get all the equipment specs, draw and dimension the house, note the orientation of the home (N, E, W, S facing), determine the construction of the home, the type of insulation, get the dimensions, locations, and construction of all the doors and windows. Put all that into heat load calculation software. From that we can determine the air flow requirement for every room and verify if the existing ductwork is sufficient or not. If it's not, we can make recommendations for system alterations. In the equipment change out scenario, by default we do not warranty an existing ductwork installation, or the overall system performance. Obviously, since we didn't design or install the ductwork, the impact it has on overall system performance is outside of our control. We'll only guarantee the equipment itself. Again, enter existing system evaluation. If the customer agrees to buy this service AND agrees to make any necessary ductwork/system alterations, then we'll be able to take responsibility for the overall system performance.

But this is the kicker. And in my opinion, its the reason why this doesn't usually happen... there could be substantial cost involved. What if all the duct needs to be replaced entirely. And you have to pay just to find that out! As humans we don't like uncertainty. It makes us feel uncomfortable. Sometimes we'd just rather not know the truth. We all like a money back guarantee with no risk. But contractors have risk and we have to mitigate that risk; otherwise, we won't be in business long. I try to mitigate the risk in such a way that its honest and transparent. It requires frank and sometimes uncomfortable conversations. Sometimes, you got to tell people things they might not want to hear and that might drive some away.

But, hopefully the evaluation will reveal that its not all that bad. Just a few minor changes. May cost extra, but at least you won't spend thousands of dollars on a new system to find out that it still doesn't heat and cool your house evenly. After all, new equipment can't fix bad ductwork. I would think that's obvious, but hey I'm an AC guy. Hope that helps. Kudos to you for reading this whole thing. Thanks and have a great day! Emitt