My parents worry about the HVAC in their (more than) 3500 sq ft house. Not worry in the sense that "we might not be able to live" but worry in the sense that "

My parents worry about the HVAC in their (more than) 3500 sq ft house. Not worry in the sense that "we might not be able to live" but worry in the sense that "turning down the upstairs thermostat a few degrees sure saves a lot of money."