Would a window unit help your electric bill decrease in conjunction with your central air which is now running all the time?

Answer 1

Hard to say, probably not much. It would depend on whether it could actually enable your central unit to catch up and shut off. If the window unit were sufficient for the room you want to have cooler, so that you can close the door and the A/C register, and raise the setting on the thermostat for the rest of the house, that could help. If the reason the central unit is running so much is that it needs maintenance or replacement, spending the money on that rather than the window unit is what would give you the best payback on your power bill. If your A/C is 15 or 20 years old, it was inefficient to start with and has gotten worse. A new, properly sized, high efficiency unit can pay for itself surprisingly quickly.

Answer 2

Using a window unit in conjunction with your central air conditioning system may actually increase your electric bill rather than decrease it, since both units will be drawing power to cool the space. It is more cost effective to optimize the settings on your central air system and ensure your home is well insulated to improve efficiency. Consider using the window unit in specific rooms instead of running both systems at the same time.