Your home is a collection of energy systems that convert fuel and electricity into light, heat, sound, and other useful forms. While these systems are interrelated, each plays a distinct role in your home's overall energy efficiency. Understanding how each system influences your home energy use helps identify opportunities for energy efficiency improvements.

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A whole systems view helps identify considerations for combining energy systems in new and interesting ways. In addition to discerning how each system impacts your home and its efficiency, a whole systems perspective can also be helpful in understanding the building's impact on the broader systems beyond the building itself.  

Site and landscaping

While two neighboring homes experience the same weather throughout the year, they may have vastly different heating and cooling needs. Climate and geography determine every building's needs for heating and cooling, including site-specific microclimates. The direction your house faces, the amount of shade your home experiences, and your exposure to winds all impact your home's energy use.

Building envelope

The outer shell of a building, known as the "building envelope," is one of its most important energy systems. This shield between the inside and outside provides a barrier to weather, air, and moisture. In short, the building envelope contains the heat and humidity of the building's interior independent of the heat and humidity outside.

A tight seal on the building's exterior will increase a building's energy efficiency. A leaky envelope can undermine a building's ability to use energy effectively and contribute to decay. Some approaches to energy efficiency, such as the Passive House standard, include a specific standard for the building envelope. Upgrades to insulation, air sealing, and windows can increase the efficiency of existing building envelopes.

Space heating

When thinking about a building's energy systems, it's helpful to distinguish space heating from space cooling and ventilation. Heating, cooling, and ventilation are separate systems that can integrate with a combined HVAC system. Furnaces or boilers, heat pumps, radiant floor heating, electric space heaters, and wood stoves all heat interior spaces. Other approaches include passive solar heating, which uses the position of windows and thermally absorptive surfaces to convert incoming sunlight into stored internal heat, mechanical systems and incandescent lighting, as well as the body heat of the people inside a building. 

Space cooling

The need for space cooling depends on climate and location. Like heating, space cooling can be provided separately or integrated with an HVAC system. Common methods to cool interior spaces include heat pumps or window air conditioners.


Ventilation systems replace stale or contaminated interior air with fresh air from the outside. In its simplest form, an open window provides ventilation and may also cool interior spaces during warm weather. Because the air temperature outside is often cold and interior air contamination is typically concentrated in specific locations and rooms, buildings often use mechanical systems with fans to move air at controllable rates.

The ventilation system is part of the home energy picture because it moves air and moisture across the barrier of the building envelope and is particularly important in energy-efficient buildings with tight envelopes. When a building's envelope succeeds in limiting airflow between the interior and exterior, it may require a ventilation system to provide fresh air to its occupants. In these cases, green homes may use a heat exchanger to recover heat from the outgoing air stream and move it to warm the incoming air in winter or the reverse in summer. Energy recovery systems can also transfer humidity, increasing the energy transfer efficiency between incoming and outgoing air.


A building's interior and exterior lighting system uses energy, typically by converting electricity into lumens. Lighting fixtures, especially old-fashioned incandescent light bulbs, emit heat as a byproduct. Green homes usually use more efficient lighting solutions, including fluorescent bulbs and light-emitting diodes (LEDs), which generate less heat and more light per unit of electricity consumed.

The arrangement of windows on a building's exterior and the natural daylight that they admit can reduce the need for artificial light at different times of the day. The arrangement of lighting can also increase the lighting system's efficiency. For example, task lights focus light in a particular space rather than lighting the entire room, delivering more usable light and less light overall.

Water heating

Water heaters consume a significant amount of energy, but there are multiple ways to improve the efficiency of a home's water heating system. If the water heater has a tank, it can be insulated to retain heat better. Tankless on-demand systems provide another approach to efficient water heating. Standard water heaters progressively lose thermal energy depending on how much the tank is insulated. Tankless water heaters eliminate the need to store thermal energy, reducing energy loss. Additionally, solar hot water heaters convert the sun's energy directly to thermal energy for water heating.

The more hot water you consume, the more you heat it. Water-saving measures, such as low-flow fixtures, have the added benefit of saving money on water bills and reducing energy use from water heating. Similarly, PEX piping delivers water between the water heater and tap quicker, lowering the time you have to wait for hot water and increasing the efficiency of the water heating system as a whole.


Homes include a variety of electronics that consume energy, such as televisions, computers, and audio systems. While the efficiency of individual electronic devices has generally increased over the last few years, so has the number of these devices. Phantom loads, or electricity consumed by devices plugged in but not in use, can significantly impact a home's energy. 

Control systems

Control systems govern and regulate the home's energy systems. For example, the thermostat governs the home's space heating and cooling systems. Smart thermostats and programmable thermostats can provide considerable energy savings by changing the timing of space heating and cooling.

Lighting timers and motion sensors can dim or turn off lighting when a space is vacant, especially in hallways and less frequently used areas. Phantom load switches eliminate the slow sip of energy from electronics and appliances that use energy even when the devices themselves are turned off. 


There's an energy-efficient model for virtually any home appliance. We'll go into more detail about these below. 

ENERGY STAR is a program run by the Department of Energy (DOE) and the Environmental Protection Agency (EPA) that certifies qualified appliances as energy efficient. In other words, ENERGY STAR-certified appliances use less energy to achieve the same output as non-energy efficient alternatives. Considering the average home appliance lasts for 10 to 20 years, replacing the appliances in your home with ENERGY STAR-certified appliances can reduce your energy bill for years to come. 

Clothes dryers

Dryers are highly energy-hungry appliances, yet 80 percent of American homes use them. Luckily, ENERGY STAR-certified dryers use less energy than conventional dryers and can cut utility costs and greenhouse gas emissions. 

Clothes washers

Generate savings on your electric and water bills by pairing your energy-efficient dryer with an energy-efficient washing machine. ENERGY STAR-certified clothes washers use 20 percent less energy and 30 percent less water than standard washers.  


Refrigerators, especially older models, are one of the biggest energy hogs in U.S. homes. ENERGY STAR-certified refrigerators are about 9 percent more energy efficient than models that meet the federal minimum energy efficiency standard. 


Dishwashers may use less power than a constantly-running refrigerator or a high-heat clothes dryer, but the electricity and water used in a dishwasher cycle add up. An ENERGY STAR-certified dishwasher can save you about 3,800 gallons of water over its lifetime.

Replacing your home appliances with energy-efficient upgrades can save you hundreds of dollars a year on your energy bill. The savings you achieve from a single energy-efficient appliance may seem small on its own, but those small monthly savings will add up over your appliance's 10 to 20-year lifetime. Between the long-term savings and state, local, or utility rebates available, depending on where you live, the price premium you pay will likely be more than offset by your energy savings.

That said, the amount of money you'll save with energy efficiency measures depends on how much you're willing to invest. For example, you can shave a few dollars off your bills by replacing incandescent lightbulbs with LEDs. To significantly lower your bills, consider replacing appliances and systems that use the most energy.

Now that we've identified the many ways homes use energy, it's important to highlight the different sources that provide it. Most homes use electricity generated from a mix of fuel sources before being transmitted and distributed across the electric grid. Natural gas or propane is also common for heating and cooking. Additional fuel sources include heating oil, wood, wood pellets, solar thermal energy for hot water, and solar photovoltaic (PV) systems for generating electricity.

Fuel switching creates unique opportunities for energy efficiency upgrades and can facilitate synergies between various home energy systems. For example, a solar-powered heat pump can replace the need for heat from other fuel sources. Depending on whether they're gas-fired or electric, water heaters, clothes dryers, ovens, and stoves can integrate with other home energy systems. You can upgrade an old boiler powered by heating oil to a highly efficient wood pellet boiler. New systems using old fuel sources, like wood, are sometimes surprisingly efficient.

Electric vehicles are another example of fuel switching. These vehicles use electricity instead of gasoline as their fuel source, and this electricity can come from the home's electrical system. Adding an electric vehicle will add to the home's electricity use, but it will eliminate the use of gasoline, a switch that typically creates significant cost savings.

Home batteries are also gaining in popularity. Batteries are part of the home's electrical system but can play a crucial role in fuel switching. By storing electricity and allowing the home to use solar electricity produced during the daytime after the sun goes down, batteries can make solar a more feasible source of electricity for more homes.

To further insulate your home against rising electricity prices, consider installing solar panels on your property to generate your own clean electricity. Interested in learning more about going solar? Sign up for a free EnergySage account to connect with our Energy Advisors, compare quotes from vetted installers in our network, and go solar with confidence.

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