>>The ONLY reason to run dual electrical circuits would be IF you simply MUST feed some non-standard electrical power (like 12v DC) and don't want the risk of accidentally plugging your fancy 12 volt washing machine into the 110v AC outlet when the line power is on... and in a case like that, your household wiring is too small to carry the required current anyway (can we say "FIRE!") - but those are pretty rare and fancy scenarios. Solid state inverters and voltage boosters are so common and (relatively) cheap nowadays as to make that a pretty desperate move anyway - it's very now easy to condition any input to standard frequency and standard line voltage. <<

I'm not sure what you have against an independent 12-volt system, but I'd love to hear you elaborate on the cons. Running separate 12-volt lines, together with a solar panel array and a series of deep-cycle marine batteries is a good way to supplement your grid power, especially in an area where the grid is frequently out or intermittent. Converters are an option, and are ok when the 110 is on. But the energy lost due to inefficiency is too high for coverters to be relied on in a "survival" situation, or one I like to call "Fort Homestead". The websites mentioned elsewhere in this thread can tell you about 12-volt systems, and you can search the web under RV equipment to find what equipment and appliances are available.