" wrote in message
oups.com...
One other thing I forgot to mention...

If I split the circuit into two 125ft runs, most of my electrical loads
I mentioned above would end up on one of the circuits. And, naturally,
my circuit breaker box is at the opposite corner of my basement from
where most of the used outlets will be.

If all the heavy stuff will be on one of the 125' circuits, you wouldn't
gain anything that way; it will still be too much and too long.
You have to get the following right, or you risk burning your house down.
No joke; don't do it unless you are darned sure you are doing it correctly.
A multiwire circuit is essentially a 240v circuit split between two 120v
circuits. If you can get the two circuits reasonably balanced, the only
current coming back on the neutral is the difference between the two; so
there is little or no voltage drop on the neutral which reduces the total
voltage drop.
Unfortunately, the dehumidifier and the heater are both big loads and
impossible to balance. Unless you can get them at the first part of the
run, you are out of luck. You could get a 240v heater (which is
automatically balanced), but I haven't seen a 240v dehumidifier.

To be sure you would have to do a detailed analysis with specific loads and
distances, but I suspect you are looking at putting in either a #10 circuit
for the big loads or a 240v circuit.