Hello, this is a great question that we frequently are asked. The approximate monthly cost to operate these systems is difficult for us to answer, as there are many variables involved. Things like, the systems efficiency rating, usage, size of system based on area its heating/cooling, local utility rates etc... To get a better idea of a fair approximation, I would recommend asking your local hvac contractor for their insights. If you let them know the efficiency rating of the system (SEER for cooling, HSPF for heating) and give them an idea of your area & usage, they should be able to use their experience and knowledge of your local area to paint you a good picture of costs.

Please note, as indicated in the square footage of your house, and the system you reference, one- 12k btu system is likely to be far too small to properly heat and cool 2000 sqft. As a general rule, 12k btu is rated for normal areas sized 400-650 sq ft. You may want to consider a total of approx 48k btu sizing (or 4 ton). We have plenty of system options that would suffice. You may want to reach out to your hvac contractor for proper sizing for your house or you can give us a call and we'll be happy to assist.

Hope this helps!