AC question

[vinylfloorguy]

What would be chearper to run, one unit on high or to two or three on low?

[agmantoo]

There are too many variables to be able to answer this accurately. The AC needs to be sized to the application regardless of the BTUs needed. Too large will waste power. All units in the calculation need to be of the same SEER and applied to the exact same house. Living habits need to be considered. Design of the house will impact the answer, etc. That said I am convinced that if the house needed a 27000 BTU and that 2 units were used instead of 1 that the utility costs would be less. An 18000 btu unit in the main part of the house and a 9000 btu unit elsewhere would permit greater the dehumidifying as the smaller unit could be run longer. With the continued running of the smaller unit the temperature inside could be permitted a couple of degrees higher and still have creature comfort. A single unit would dehumidify less due to cycling at a set temperature that would be higher to achieve the same creature comfort level. Properly done, the two units could be adjusted to determine which one required running to achieve comfort and the other left off in many situations. The chances are good that the smaller unit would be all that is required once the house has reached the desired temperature and the smaller unit would continue to dehumidify. During the peak of the day the second unit could be phased in if the heat elevated.

[cfabe]

If the units are identical window units, one unit on high will be cheaper to run. A window A/C uses about 95% of the power to run the compressor and 5% to run the fan. The low/high only changes the speed of the fan, the compressor only has one speed.

[WayneR]

Close off all areas of the building you don't need to be in by closing doors and covering windows to reduce heat build up those rooms.

If the window units are in the sun, try to shade them also, as it will help reduce their operating temperature.