If you are installing new equipment, you will need to decide whether to pay extra for various features. Here are some of the most common add-ons worth considering:

Variable-speed blowers: Indoor fans (blowers) and/or outdoor fans of central air conditioners, heat pumps, and furnaces can be equipped to run from slow to fast, depending on need. The units are programmed to keep conditioned air continually moving at the lowest flow possible. These setups minimize cycling on and off (which contributes to wear and tear), dramatically help systems maintain consistent temperatures throughout different areas of homes, reduce energy usage, and decrease noise.

Variable output: Furnaces with this feature automatically select how much heat to generate, usually from between two levels; air conditioners and heat pumps with variable output automatically select how hard their compressors need to work to deliver conditioned air. Like variable-speed blowers, this feature lets equipment deliver warm or cool air continuously for longer periods of time, meaning equipment doesn’t have to cycle on and off frequently.

Programmable thermostats: These devices provide an easy way to save energy. If your home is unoccupied during the day, you can save five to 15 percent per year on energy bills by turning down the heat by 10F° to 15F° while you are away. A misconception associated with programmable thermostats is that when it is time to return the temperature to normal, the furnace has to work so hard, and use so much energy, that little energy is saved. Much research has shown this to be untrue. Unfortunately, many homeowners who have programmable thermostats don’t use them, but new models make programming a snap; popular ones made by Nest and others even attempt to program themselves.

Humidifiers: These can be added to ductwork and supplied with water from plumbing to make air more humid during dry winter months. Also, humid air feels warmer than dry air at the same temperatures—which means you can dial down your thermostat by a few degrees and not notice the difference. Avoiding overly dry air reduces itchy skin, eyes, and throats, and helps asthma sufferers.

High-efficiency air filters: These assemblies, which use electrical charges to attract and trap particulates, can also reduce the amount of dust blown through systems. But there’s little evidence that they actually improve indoor air quality.

Desuperheaters: Some high-efficiency heat pumps can be equipped with these devices that capture waste heat generated from heat pumps during cooling mode and use it to heat water. Desuperheaters heat water two to three times more efficiently than conventional electric water heaters.