As a heating and cooling professional, I have several tips up my sleeve to help with lowering the cost of your monthly utility bill, the first tip is to only run your central cooling system or furnace when you are home, many times people will forget to turn off the cooling system or heat when they leave for an extended period of time, and this will only make your utility bill go up.
How many people like to keep their central cooling system or furnace running throughout the day while they are at work so that they can come home to an cooling system or warm home, and for these people I would suggest getting a smart thermostat device so that you can set up a schedule that will cause your central cooling system or boiler to turn off when you are at work, and to turn on when you are on your way home.
Another suggestion is to keep your windows and doors shut while the HVAC units are running. Many times kids will open a window in the home and forget to shut it, causing the cool air from your mini split cooling system, or the heat from your hot water boiler to go outside rather than do its job of heating or cooling your home, then some summer afternoons it is nice to open the door and let the fresh air flow through the house, if this is the case, just go to your control device and turn off the cooling system so you are not wasting energy and money. These are just a few ways to keep HVAC costs low.