Title is pretty much it. I've got a 200 amp main panel and a 125 amp sub panel on the other end of the basement. I need to add four 220v circuits (an air compressor, two network racks, and what's basically a glorified hot plate). The sub panel is in the basement right below the garage and kitchen and the network racks are going to live ten feet from the sub panel in the basement, so I'd rather add circuits there.
The house is about 30 years old, and both the main and sub panels are in good shape. The main panel has six slots available (though they're three per side) and it's far enough away to make it less attractive for these loads, and I'd like to add other circuits to that end of the house eventually.
All the sub panel slots (16 of them) are full. It's got both HVAC air handlers and compressors, a pool pump, and all the kitchen. I can pull it off and replace it with the biggest sub panel I can find (or biggest up to the amperage, I guess), or I can add another sub panel off the existing sub panel (a sub-sub-panel?).
Here's the main panel, and here's the sub-panel. The house is about 5000 square feet, and that sub-panel serves both HVAC systems, the refrigerator, oven, and stove, and the washing machine and (electric, 220V) clothes dryer. It's also serving a swimming pool sub-(sub-?)panel. This sub panel is most of the draw of the house--the main panel is just lights and wall plugs and feeding this sub-panel.
I know I can replace this sub-panel with a larger (in terms of available slots) sub-panel or just install another sub-sub-panel to accommodate the new circuits. An additional panel would go right next to this one, in terms of location. My question is more, "what's the 'better' approach?" Are there good reasons for or against just pulling this sub panel and replacing it with one with more slots? Or will I wish that I'd just put another 16-slot sub-panel right next to this one in a year?