Furnaces and air conditioners, or, more briefly, HVAC systems, have gotten far more efficient in the last decade or so. And now, with options like geothermal and radiant in-floor heat, homeowners can achieve efficiency, comfort and cost savings like never before.

This may have you thinking about a new HVAC system for your own home. But how do you know when it’s really time to replace the equipment you have? If you consider these five characteristics of your current HVAC system and home, you’ll be better prepared to replace it on your terms, not when it decides to break down at the moment you most need it:

1. Your System’s Age

Experts say that if your system is more than 10 years old, you should definitely consider replacing it. Older systems that are in need of replacement are less efficient, can’t keep up with your heating and cooling needs, and are often noisy. An HVAC system usually works until it’s about 20 years old, but it will start costing much more once it hits that 10-year mark. And if your heat exchanger is old—you can smell exhaust and see soot or water—you need a new system. You also miss out on more efficient innovations like better compressors and programmable thermostats.

2. Your Current Costs

If your current HVAC system is starting to cost you more, it’s time to shop for a new one. As your system ages, it becomes less efficient and you’ll notice your energy bill rising. New HVAC systems can save you at least 20 percent on your bill due to more efficient design, so you may want to do the math and see how long it would take to make your money back on an update.

3. Your Home’s Comfort

If you start having air-quality issues in your home, you need a new HVAC system. Older, worn-out systems blow dust back into your home, even after you’ve changed the filters. Also, a system with a bad heat exchanger will leave your entire house smelling like exhaust. A new system will relieve these problems. Also, you know it’s time for a new HVAC when your old one can’t keep your house at a comfortable temperature. Stop messing with the thermostat and install something new.

4. Your System’s Safety

Older HVAC systems are less safe to run than newer systems. If you’ve got a gas furnace that’s older than 10 years, you should definitely consider a new one. Newer gas systems usually have electric pilot lights, rather than the old “always on” pilots which can start to leak carbon monoxide into your home. Older systems of any kind also can develop leaks and cause your home to fill with dangerous CO or other toxic fumes and dust.

5. Changes to Your Home

Finally, if you are considering changes to your home, you need to also consider a new HVAC system. If you’re planning an addition or large remodel, adding a lot of area to your house, you’ll need a new system that’s rated to cover the added space. Or, if you’re planning to sell your home, you may want to replace an outdated system to add value to your home. You can usually make a good return on that kind of investment at sale time.

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