According to TURTLE :
The 120V vs. 240V line-loss isn't necessarily insignificant, even well
under circuit capacity.

Ie: given the exact same wire-size between a 120V and 240V circuit
(which'll be often the case with a window-mount AC), the 240V circuit
will lose 1/4 as much power to supply line losses as the 120V circuit
does. At, say, 120V/10A with a circuit long enough for a 3V voltage
drop, that's 30W at 120V, but only 7.5W at 240V. 30 hours of that at
120V is about 1 Kwh of lost-inside-house-walls power. 8-16 cents/day,
vs 2-4 cents/day. That may or may not be significant depending on your
own personal criteria.

What your saying here is a condition that most of the time will not be
in effect for Electrician will size wire for a little more than the max
the wire will handle. If you had a 3 volt drop on a 120 volt circuit.
Your taxing the wires ability at least and need to change the wire out
to not even have a 3 volt drop to start with.

10A is well within the rated ampacity of even a 14 ga circuit even after
80% derating, and 3V is _less_ than both the NEC or CEC IR drop maximum.

If you don't give a damn
about a job. You just put the least it will get by with and let the
customer pay for it the rest of their life. Any circuit with a 10 amp
draw on it needs atleast a # 12 wire on it 120 volts or 220 volts. I
run circuits for my equipment and if I see a 3 volt drop. i would
change out the wire atleast to not have it. I would have nothing with a
3 volt drop on it.

I have no quibble with the fact that you'd consider a 3V drop excessive,
and would up the wire. And indeed, for built-in central A/C, I think
any good electrician or HVAC installer should and would consider doing
exactly that.

However, we must face reality here. In the vast majority of mass built
homes, electricians are often simply not going to think about this at all
for general circuits (the context being, I think, a window-mount A/C
on a general outlet circuit). And of those that do, few would consider
a 3V drop excessive either.

Not to mention the startup surge, which will probably at least triple
the drop momentarily (triple power loss and increased compressor start stress).

Now the Thread is a Home owner asking about it cost 1/2 the power cost
to run the equipment on 220 volts verses 120 volt service.

No, we got one of the answerers suggesting that. Once you exclude
that bit of nonsense (which seems to pop up every time someone asks about
120V vs. 240V - I think the stupidity level is remaining constant
despite everyone correcting them EVERY time), a few percent of power
lost in the wiring MAY well be significant to the OP.

And do remember that that, say, 3% loss to supply wire heating may increase
total power consumption by more than the 3%. If you lose 3% heating up the
supply lines, another 3% of your A/C capacity may get chewed up trying to
get rid of it, so the inefficiency could theoretically double.

[worst case, exceedingly unlikely in practise, but you get the idea.]

You pay
ruffle the same as 220 volt or 120 volt service. 1/2 the cost to
operate is not in the picture.

Absolutely. But I don't think that's where the OP was, nor what they
were thinking, just one of the more ignorant responses.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.