Custom Duct Transitions For AC Coil

Installing a new AC coil

There are times when installing a new AC coil to existing duct work can be simple and times when the task can be difficult. Usually you can get the proper cased AC coil for the furnace you are installing and either easily transition the duct to the existing duct line or you can have a custom plenum made fitting the coil to the furnace.  

Then there are times when you need to transition from your furnace to the size of the uncased AC coil and then back again to the custom size of your existing duct work. When this happens your first call should be to us, K & E Sheet Metal, because this is exactly why we exist. Custom plenums and transitions are our specialty :)

Taking measurements 

Today we received an order for a plenum with transitions needing to get from one measurement, to another and then back to yet another. Below is a crude drawing of the sizes needing to be transitioned. 


In order to make the transitions and fit the AC coil, I will need to fabricate two transitions and a straight plenum, placed in the center, that will house the coil and have a door for servicing. The transitions can be entered into the computer system and cut with our new CNC plasma machine, while the straight box I will cut with tin snips. 

Looking down inside the AC coil plenum at the shelf that will hold the coil

Looking down inside the AC coil plenum at the shelf that will hold the coil

The fabrication

The bottom transition, 13 1/4 x 18 up to 17 1/4 x 19 3/4 will have a 1/2" flange on the new furnace side and S-lock on the top side that will accept the straight plenum box. Inside the plenum box will be a 24 gauge metal shelf (Picture to the right) to hold the AC coil inside the 17 1/4 x 19 3/4 box.

From the top of the AC coil box I will transition to the existing duct inside the customer's home. Basically, the old duct work leftover after tearing out the old furnace. 

All being said the fabrication for this order sounds much harder than it actually is. Many times the hardest thing is translating what the customer is thinking into how my brain processes things. Once this hurdle is completed the process goes rather quick and easy. This particular order foe example ended up being two simple custom transitions with a straight AC coil box sandwiched in between.

Below is a photo of the finished plenum ready to be picked up and installed


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