Once an HVAC unit lasts over a decade and a half, then it is on its way out. However, some people, especially the old school generation, may try to hold on a little longer, especially when there are no apparent reasons to let the system go. This may be what logic demands, but with proper scrutiny, one may discover more severe issues that warrant the old AC or furnace’s exit after a specific time limit. However, before this happens, you may want to keep a watchful eye on a few signs and symptoms. Top on your list should be the significant increase in energy bills. If you are consecutively receiving high bills, say three months following each other, there is a need for alarm. You need to find out why this is happening and rectify it immediately. You may have to call the HVAC technician for a professional check if none of your troubleshooting hacks seems to work. Strange noises and sounds that seem not to go away even after changing filters and cleaning essential components is another major indicator that the unit needs to be replaced fast enough. In most cases, calling an HVAC contractor is the easiest way to confirm this. If you are still in doubt, then strange odors should be the red flag you don’t ignore. More often than not, such strange odors are indications of serious underlying problems. In case the HVAC unit seems to have so many issues at a go, the easiest thing to do is to talk to the experts for advice on the best replacement unit.