The answer to 'when to replace HVAC system' is that most HVAC systems need to be replaced every 10-15 years, depending on the equipment and how well it has been maintained. Signs it's time to replace your HVAC system include increased energy bills, more frequent repairs, and the system not keeping your home as comfortable as it used to.
As HVAC systems age, they become less efficient and more prone to breakdowns. Replacing an old, inefficient system with a new, high-efficiency model can save you money on your utility bills and provide more consistent comfort in your home. It's generally recommended to replace your HVAC system before it completely fails to avoid being left without heating or cooling.