Understanding Home Energy

The average home in the U.S. uses the majority of its energy for space heating, followed by water heating, air conditioning, and lighting. However, it is important to identify the major energy users in your home specifically because Maryland’s climate can vary significantly from one region to another while energy prices may fluctuate from one year to the next. Conducting this analysis can help you understand where energy and money are spent and can focus your priorities for making energy efficiency improvements.

How can I determine the baseload?

There are a number of ways to determine where your home uses the most energy. Analyzing your energy bills from the previous 12 months can help you understand how much energy you use for your ‘baseload’, heating, and cooling. A home’s ‘baseload’ is the amount of energy used under the least demanding set of conditions (when energy use is lowest).  In general, electricity use is higher in the summer months due to the use of home cooling systems; while natural gas is higher in the winter months due to home heating systems (see Table 1). For electricity in Maryland, this is typically in the spring or fall when no cooling is required, when furnace fan use is minimal, and when natural lighting is fairly abundant.

Electricity is predominately used for appliances, lighting, electronics, and other small loads. In this case, the annual electricity baseload for this home can be calculated by multiplying the monthly low of 550 kWh (October) times 12 months = 6,600 kWh. At $0.08 per kWh, this home spends $528 per year on its baseload electricity use. To understand how much electricity is needed to cool the home, multiply the monthly electricity baseload of 550 kWh times the number of warm months in which there is a spike in electricity use. As expected for Maryland, there are 5 warm months (May-September). Subtracting the baseload electricity used during the warm months (2,750 kWh) from the total electricity used during the warm months (3,990 kWh) yields 1,240 kWh. At $0.08 per kWh, this home spends almost $100 per year on electricity for cooling. 

Natural gas is predominately used in space heating, water heaters, and stoves/ovens. In Maryland, the annual natural gas baseload occurs in the summer when no space heating is needed. In this case, the baseload can be calculated by multiplying the monthly low of 10 therms (July and August) times 12 months = 120 therms. At $0.45 per therm, this home spends $54 on its baseload natural gas use. To understand how much natural gas is needed to heat the home, subtract the annual natural gas baseload (120 therms) from the annual total (750 therms) = 630 therms. At $0.45 per therm, this home spends around $284 per year on natural gas for heating.

How can I reduce my energy demand?

Energy ‘demand’ is the amount of energy needed to achieve certain functions, such as maintaining a comfortable temperature or level of light, drying clothes, and freezing food. When most people talk about ‘conserving’ energy, they are really talking about reducing energy demand. Reducing demand can be done in a number of ways, many of which are simple behavior changes.

Lighting demand can be reduce by allowing natural light into the home through windows.

Hot water demand can be reduced by setting the water heater to 120 degrees, taking shorter showers, only running full dishwashers, running clothes washers with cold water, and insulating pipes and water heaters.

Electricity demand can be reduced by unplugging appliances when they’re not in use.

Heating and cooling demands depend on how we address uncomfortable temperatures by adding or removing warm air during the colder and warmer seasons, respectively. The warm air lost through the ceiling, walls, windows, foundation, and air leaks in the building envelope during the colder seasons must be regained through some combination of internal heat (i.e. body heat, lights, etc.), solar heat, and active heating system (e.g., furnace or boiler). In warmer seasons, hot air enters homes through direct solar radiation, leaks in the building envelope, internal heat, and by transmission through the building interior. You will have less need for active energy systems (e.g., HVAC, water heaters, and artificial light) by minimizing your energy demand through passive techniques (e.g., air sealing, shading, and insulation). 

The whole-house approach considers the entire house to be an energy system made up of interdependent parts. For instance, the benefits of an energy-efficient air conditioner are lessened when a duct system leaks, windows don’t close tightly, the attic is uninsulated, and humid summer breezes are drifting in under the door. The whole-house approach recognizes the interaction of windows, attics, foundations, mechanical equipment, and all other components and assemblies within the home. Changes in one or a few of these components can cause changes in how other components perform.

• Why is the whole-house approach important? 

  The whole-house approach considers the entire house to be an energy system made up of interdependent parts. For instance, the benefits of an energy-efficient air conditioner are lessened when a duct system leaks, windows don’t close tightly, the attic is uninsulated, and humid summer breezes are drifting in under the door. The whole-house approach recognizes the interaction of windows, attics, foundations, mechanical equipment, and all other components and assemblies within the home. Changes in one or a few of these components can cause changes in how other components perform.
   

• How can I design/renovate my house for energy efficiency?

  The following tips may be considered when designing and/or renovating your home to improve its energy efficiency.

  House shape and orientation both play an important role in determining the home’s energy efficiency. For example, simple layouts and compact housing designs generally gain less heat in the summer (and lose less heat in the winter) compared to irregularly-shaped homes since their building envelopes have smaller surface areas for heat exchange to occur. The term “building envelope” refers to all of the external building materials, windows, and walls that enclose the internal space. Heat is transferred through the building envelope at different rates depending upon the efficiency of the materials. In general, the home should be oriented with its longest axis running from east to west to reduce the total surface exposure to the summer sun; while maximizing southern exposure to low-angle rays in the winter. It also uses fewer building materials, and simplifies the length and complexity of mechanical duct runs and plumbing pipes. 

• Window placement on the south side of your home may allow solar heat to enter the home in the winter due to the low-angle rays at that time of year, while proper overhangs can minimize the sun’s impact in the summer. Fewer windows on the east- and west-facing walls may also help to reduce solar heat gain in the summer. External shade for windows can also be provided on the east and west walls using trees, shutters, screens, or window films.

  Room layouts within the house should be based on their function and the time of day they are used. For example, primary living areas (e.g., living rooms, dens, or great rooms) should be on the south side, to provide year-round moderate temperature control; with the low sun angles in the winter providing passive solar heating. Kitchens and laundry rooms should generally not be on the west side as these they contain heat-producing appliances (e.g., oven, range, dishwasher, clothes washer, and dryer) that will compound the afternoon heat buildup. Seldom-used rooms (e.g., closets, bathrooms, utility/storage, or stairs) may serve as “buffer zones” on the east and west sides of the home to keep heat out of primary living areas.

  Outdoor areas such as porches or patios can extend your living space outside the conditioned (heat and/or cooled) areas of your home. The north side can be shaded for summer use while the south side can be for winter use.

There are two steps to the whole-house approach: 1) reducing energy demand; and 2) using efficient equipment.

How can I reduce my energy demand?

Heating, cooling and ventilation systems (HVAC) generally account for about half of the energy use in a home. HVAC efficiency impacts the temperature and humidity within the home and is highly dependent on the structural features of the home. Taking a step-wise approach to energy conservation, equipment replacement, or home renovation will help ensure a balance between thermal comfort and energy efficiency. The whole-house approach to energy efficiency dictates that instead of utilizing large heating and cooling systems, it is more cost-effective in the long-term to decrease the forces that make us uncomfortable in the first place. This means: 1) reducing air leakage by air sealing; 2) slowing the transmission of heat with insulation and energy efficient windows; and 3) making solar heat work to our advantage by managing windows and window coverings and also by landscaping for energy conservation. In addition, sealing and insulating ducts prevent the hot and/or cold air generated by heating and cooling systems from getting wasted on their way to living spaces. Utilizing a thermostat can also reduce our heating and cooling demand.

Air sealing involves sealing cracks and gaps around windows, doors, plumbing, electrical and venting penetrations so that you can control air exchange and ventilation. Sealing any leaks in these areas with caulking and/or weatherstripping will help to prevent unconditioned air from making its way into your house while minimizing the load on your HVAC system.

Ductwork should be visually inspected for gaps and/or disconnected runs. Use mechanical fasteners to secure ducts, mastic sealant to seal gaps, and insulation to prevent radiation loss. Leaky ductwork can cause major loss in energy efficiency with the conditioned air being released into undesirable locations (e.g., attic or crawlspace). As this cool air is lost to the environment, your living space will be replaced with hot humid air; doubling the strain on your HVAC system.

Insulation should first be added to the attic with at least an level of R-30 on the southeast side as roof temperatures can easily reach over 140°F. While floor and wall insulation are generally less important due to the high cost and low impact compared to other energy efficiency measures, homes with raised wood floors and crawlspaces may benefit from insulation in the winter. Slab on grade foundations may also reduce HVAC load in cooling dominated climates.

Windows should be properly sealed using caulking and/or weather-stripping. Exterior shading may be added on the east, west and south sides of your home with properly placed trees, awnings, tinted window film, or solar screens to block solar radiation. Interior blinds or drapes may provide additional shading, but may limit natural lighting. While older windows may be replaced with double pane, low-e windows, this option should be implemented before any HVAC replacement occurs since window efficiency plays a large part in the size of your HVAC equipment.

HVAC systems should be regularly maintained to ensure that your home continues to perform at peak energy efficiency. This includes replacing air filters often, cleaning condenser coils, straightening coil fins, and cleaning condensate lines. Qualified HVAC technicians should also check refrigerant levels, test for refrigerant leaks, check the air flow, and test the electrical controls.

Lighting and appliances should be replaced with more energy efficient options or models as needed. While reductions in the energy consumption of individual upgrades do not contribute as greatly to the systems approach, these upgrades may produce less heat; lowering the cooling load on your HVAC system. For example, replacing a 60 watt incandescent lamp with an equivalent compact fluorescent lamp can reduce the energy use and waste heat by 78% and 75%, respectively. Similar circumstances hold true for other household appliances (e.g., refrigerators, clothes dryers and water heaters).

What energy efficient equipment can I use?

Energy efficient equipment can be implemented in your home after reducing its energy demand. In doing so, you may find that some equipment may be smaller or even unnecessary after energy demand is reduced. Although the up-front cost of more efficient equipment is higher than standard equipment, financial incentives and long-term reductions in energy use can offset much of these additional costs.

To more fully illustrate the impact of both reducing demand and using efficient equipment, Table 2 provides a sample comparison between: A) a conventionally air-sealed and insulated home with a large, inefficient furnace; B) a tightly-sealed, well-insulated home with a small but inefficient furnace; and C) a tightly-sealed, well-insulated home with a small and efficient furnace. In comparing the conventional home (column A) with the tightly-sealed, well-insulated home (column B), the initial investment in an effective building shell (air sealing and insulation) is somewhat offset by the less expensive cost of a smaller furnace. The purchase of the high efficiency small furnace (column C) significantly increases up-front costs. Both the investments in the building shell and the efficient equipment save a significant amount of money over the lifetime of the upgrades when compared to the conventional option. Financial incentives (like utility rebates) would make the up-front investments less expensive.

* 1 air change per hour; average of R-18; 60,000 BTU and 80% efficient furnace
† 0.35 air changes per hour; average of R-24; 40,000 BTU and 80% efficient furnace
‡ 0.35 air changes per hour; average of R-24; 40,000 BTU and 95% efficient furnace

Another feature of the whole-house approach is that investments in energy efficiency can decrease the costs of renewable energy. If an energy efficient home uses 10% less electricity compared to a conventional home, for example, one would require a smaller solar photovoltaic system to offset electricity use (see Table 3).

* Assumes 5.5 kWh/m2/day; a 0.77 derate factor; $4/Watt installation cost; and no financial incentives
† 0.35 air changes per hour; average of R-24; 40,000 BTU and 80% efficient furnace
‡ 0.35 air changes per hour; average of R-24; 40,000 BTU and 95% efficient furnace

It is important to understand the whole-house approach to energy conservation and efficiency in order to make sound long-term energy investments. Determining your home’s baseload, heating, and cooling energy use is one way to get started prioritizing energy decisions. With a better understanding of where energy is being used in your home, you can focus on reducing energy demand through energy conservation and efficiency measures. Reducing your energy demand can result in long-term savings in ongoing energy costs. Becoming energy efficient can increase comfort as well as decrease the cost of renewable energy systems.

For more information on the whole-house approach and any potential changes that you might be able make to your home for improved energy conservation and efficiency, visit:

• U.S. EIA (2018): Space Heating & Water Heating Account for Nearly Two Thirds of US Home Energy Use
• U.S. DOE, EERE (1999): Systems approach cuts home energy waste and saves money
• U.S. DOE, EERE (2003). Whole-House Energy Checklist: 50 Steps to Energy Efficiency in the Home
• U.S. DOE, EERE (2009). Whole-house Systems Approach
• University of Florida, IFAS (2008). Energy Efficient Homes: Incentive Programs for Energy Efficiency

For more information on air sealing visit:

• ENERGY STAR: Why Seal and Insulate?
• Iowa Energy Center (2012). Home Series-1: Home Tightening, Insulation and Ventilation
• U.S. DOE, EERE, Energy Savers: Caulking and Weatherstripping
• U.S. DOE, NREL (2001). Weatherize Your Home—Caulk and Weather Strip

For more information on ductwork visit:

• U.S. DOE, EERE, Energy Savers: Minimizing Energy Losses in Ducts
• University of Florida, IFAS (2017). Energy Efficient Homes: The Duct System

For more information on insulation visit:

• U.S. DOE, EERE, Energy Savers: Insulation Materials

For more information on windows visit:

• ENERGY STAR: Why Seal and Insulate?
• University of Florida, IFAS (2019). Energy Efficient Homes: Windows and Skylights

For more information on HVAC visit:

• ENERGYSTAR: Heat & Cool Efficiently
• U.S. DOE, EERE: Energy Savers: Air Conditioning
• University of Florida, IFAS (2018). Energy Efficient Homes: Air Conditioning

For more information on lighting and appliances visit:

• U.S. DOE, EERE: Energy Savers. How Energy-Efficient Light Bulbs Compare with Incandescents
• U.S. DOE, EERE: Energy Savers. Purchasing Energy-Efficient Light Bulbs
• U.S. DOE, EERE: Energy Savers. Appliances and Electronics
• University of Florida, IFAS (2018). Energy Efficient Homes: Appliances in General