Our home has an open floor plan, we have two AC units. I have been leaving the upstairs unit turned off because normally there is only my wife and I here. I noticed that when the upper unit is on the lower unit does not run as long so I decided to leave both units on. Currently I have the upper unit thermostat set at 79 and the lower at 77, Is running both units more efficient than one? Or am I just running up my electric bill?

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Originally Posted by punder

Our home has an open floor plan, we have two AC units. I have been leaving the upstairs unit turned off because normally there is only my wife and I here. I noticed that when the upper unit is on the lower unit does not run as long so I decided to leave both units on. Currently I have the upper unit thermostat set at 79 and the lower at 77, Is running both units more efficent than one? Or am I just running up my electric bill?

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Cold air falls. That is the reason the lower unit does not run as much when the upper unit is running since the upper units cooling capacity is helping out the downstairs unit since the upstairs cool air is falling down to the lower area thus helping out the cooling for the downstairs area. Hope you can understand that.

As far as both units running I always say let your wallet be your guide. The more you spend on utilities the more comfort you will have and the lower temperatures on both levels.

A zone system like you and I have does have the advantage to save $$$. In my home we only cool the areas we are using at the time of usage. This way we are not spending cooling dollars for an unoccupied space. Before we use the bedroom at night we have it programmed to start the cooling about 1 hour before bed time. This keeps us comfortable and saves money.