Noon-Air wrote:

We can't *see* it from here. Call your local, *competent*, licensed,
insured, professionally trained, HVAC technician to do a complete assesment

Try to find one who can spell :-)

"Nehmo" wrote:

If a house currently has multiple window air-conditioners, are these
significantly less efficient than central air, if the house were
retrofitted with it?

Maybe, but they cost a lot less, with no ducts or concrete pads or plumbing
or special electrical wiring, and low-cost Chinese and Korean labor, vs
local HVAC criminals. At $69 for 5340 Btu/h at 10.2 EER (Daewoo), a 3-ton
system is $69x36K/5340 = $465.17. And if one breaks, the rest keep working.

...about half the rooms are normally in use;

So you might close the doors and only AC those rooms, effectively doubling
the SEER of the window units, compared to central air. An X10 system with
occupancy sensors might do this automatically.

A companion question is, does the efficiency of air conditioners
increase significantly with size?

Yes, by law :-)

Nick