Any Electricains on the Board?

[powerboy]

What you have to do first is determine your total load in the house at any given point. For example, if you are a power hog and on average use 50 or 60 amps (not likely) then you are limited to how much more you can draw from the 100amp. If you are an average user of electricity, adding a sub panel is not a problem at all.

What would happen is something like this...

The 2 spaces you have left would be filled with say a 50amp (example)dual pole breaker. A line (correct gauge for load) would run to another box close to your tank. A small sub panel with a couple breakers in it is wired to the appropriate duplex plugs.

If you are going to go this route, may i suggest finding out what on your system can run on 220v and wire it accordingly. It will save precious amps resulting in a smaller breaker(s) wire, and ultimately cost. (Cost to install, not power usage, its the same)

To answer the question about the 20amp duplex's, by code, you need to install those plugs to differentiate between the two. Using a heavy duty 15amp duplex will do the same thing, just cheaper.