Not everyone knows that an AC transformers can be connected in parallel on the outputs to increase the total power output. A single 50VA transformer (like the one ZoningSupply.com offers) is capable of about 2 amps of output at 24VAC. This is more than enough for most typical systems up to 4 zones that have only 1 or two dampers per zone, however, some situations call for more dampers. If this is the case for your application, you can find some 75VA or even 100VA transformers for sale, but there is another way. If you use two transformers and connect them as shown in the image below, you will have a 100 VA output.
One critical detail to note, these MUST be connect with the same “POLARITY” In other words, the two terminals on the left of the transformers must connect together and the two on the right must connect together.
It would be a good practice to plug both of these transformers into the same power strip to also ensure that the polarity is maintained on the 120Vac input as well.