The power factor of a house refers to the ratio between the real power consumed by the house’s electrical loads and the apparent power supplied to the house. Real power is measured in watts (W) and does useful work like running appliances and lighting. Apparent power is measured in volt-amps (VA) and accounts for reactive loads that do no real work like motors and transformers. The power factor ranges from 0 to 1, with 1 being ideal. A higher power factor means more of the supplied power is being used effectively. The average power factor of a residential house is around 0.85.
What affects a house’s power factor?
There are several factors that influence the power factor of a house:
- Types of loads – Inductive loads like motors, transformers, and fluorescent lighting cause reactive power draw and lower power factor. Resistive loads like incandescent bulbs and heaters use real power and have higher power factors close to 1.
- Size of loads – Larger motor loads like air conditioners, pumps, and appliances have lower power factors than smaller loads. The ratio of motor loads to resistive loads impacts the overall house power factor.
- Power supply – Long cable runs from the utility pole transformer can cause increased inductance and lower power factor. Overloaded distribution lines also contribute.
- Power corrections – Installing capacitor banks can compensate for reactive power and raise low power factors closer to 1.
Typical range of house power factors
While 0.85 is an average, power factors can vary among different homes depending on their size, construction, and types of electrical equipment used. Here is a typical range:
- Older homes with outdated wiring – 0.65 to 0.75
- Homes with a mix of motors and resistive loads – 0.75 to 0.85
- New efficient homes with modern lighting and appliances – 0.9 to 0.95
- Homes with power factor correction – 0.95 to 0.99
Very old houses from the 1950s or earlier often have poor power factors down to 0.6. All-electric homes with many large inductive loads can be below 0.7. Newly built homes tend to have higher power factors thanks to energy efficient lighting like LEDs and CFLs, as well as better wiring.
How power factor affects electricity bills
A lower power factor increases costs for both the homeowner and the utility company. With a lower power factor:
- More current is required to deliver the needed kW of real power
- Greater losses occur in transmission lines and transformers
- Voltage drops are higher from increased reactive power
To recover costs for supplying excess current and managing reactive power, utilities may charge commercial customers and industrial facilities penalty fees for low power factors below 0.9. Residential customers are not charged penalties but still pay higher bills from drawing extra apparent power.
Methods to improve house power factor
Here are some ways homeowners can cost-effectively raise their power factor closer to 1:
- Replace incandescent bulbs with LED lighting
- Upgrade older appliances and HVAC systems with energy efficient models
- Have a professional perform power factor correction
- Install solar photovoltaic panels to supply real power
Targeted capacitor placement is the most effective way to cancel out reactive power on specific motor loads. Capacitors can raise power factors to 0.95 or better.
Power factor case study examples
Here are two example scenarios demonstrating how the power factor might differ between households:
Older home with outdated wiring and appliances
- 1960s home with original 60 amp electrical service
- Loaded down with multiple window AC units
- Still uses incandescent and fluorescent lighting
- Has an older 1/2 HP pool pump motor
- Long cable run from utility pole transformer
This home would likely have a power factor around 0.7 due to significant reactive power draw from old AC units, fluorescent lighting, undersized wiring, and an inductive pool pump motor. Installing 600 volt-amp capacitors near the AC units and pool pump could raise the power factor to 0.85. Further lighting upgrades would improve to around 0.9.
New all-electric home meeting modern energy codes
- 200 amp electrical service
- High efficiency heat pump HVAC system
- All LED lighting
- EnergyStar rated appliances
- Short utility cable run
This type of new construction home would have a higher power factor around 0.93 thanks to predominantly resistive loads. LED lighting, short cable runs, and right-sized wiring minimize inductive losses. With a few capacitors near the HVAC components, the power factor could reach 0.97.
How power factor affects voltage
Reactive currents from low power factor loads can cause increased voltage drop in a house’s electrical system. Greater current draw due to lagging power factor leads to higher I2R losses in conductors and components. This results in lower voltage available to operate lights and appliances. Sensitive electronics may experience interference or shut off entirely if voltage drops too far out of specification.
Voltage drops are usually only a concern in homes with undersized wiring or excessive loads for the service size. Running new dedicated circuits or upgrading the main service panel may be needed in addition to power factor correction. Keeping loads balanced across phases also minimizes voltage issues.
Power factor trends over time
Average residential power factors have improved gradually over the decades as older, less efficient building practices and equipment are replaced with modern standards and technology:
| Era | Typical Home Power Factor |
|---|---|
| Pre-1950s | 0.60 – 0.70 |
| 1950s-1960s | 0.65 – 0.75 |
| 1970s-1980s | 0.70 – 0.80 |
| 1990s-2000s | 0.80 – 0.88 |
| 2010s+ | 0.85 – 0.95 |
Very old homes with knob and tube wiring, undersized services, and outdated appliances tend to have power factors in the 0.6 range. As residential wiring improved to handle larger loads and more efficient appliances came into use, average power factor slowly increased decade over decade. Today’s homes with the latest lighting and equipment can achieve high 0.9 power factors.
Regional differences in house power factors
There are some regional trends in average residential power factor based on predominant housing ages, construction methods, and types of heating/cooling equipment used:
- Northeast – 0.8 to 0.86 – older housing stock, increased use of electric resistance and oil heating
- Midwest – 0.82 to 0.88 – mix of older and newer homes, central AC common
- South – 0.83 to 0.9 – high use of central electric air conditioning
- West Coast – 0.85 to 0.92 – newer construction, temperate climates, gas heating
The highest power factors are generally found in warmer southern states that make greater use of central air conditioning. The lowest averages are seen in cold northern regions with older homes that have not been updated. Mild western climates allow for more energy efficient construction. Targeted power factor correction in areas with older building stock could improve regional efficiency.
International comparisons of residential power factor
Power factors also vary globally based on economic development, building codes, and electrification rates. Some general trends by region:
- North America – 0.85 average
- Europe – 0.80 to 0.83 average
- Asia – Developed nations: 0.85 avg. Developing nations: 0.70 to 0.75 avg.
- Latin America – 0.70 to 0.85 average
- Africa – 0.60 to 0.75 average
More established economies with modern grids, construction, and appliances maintain higher residential power factors. Developing nations with incomplete electrification, informal housing, and lack of standards tend to have lower power factors. However, developing countries are rapidly improving with better infrastructure investment and economic growth.
Typical power factors for household loads
Power factors vary widely for different types of residential electrical equipment. Typical power factor ranges:
| Device | Typical Power Factor Range |
|---|---|
| Incandescent lighting | 0.95 – 1.0 |
| LED & CFL lighting | 0.90 – 0.99 |
| Motors | 0.40 – 0.85 |
| Heat pumps | 0.85 – 0.95 |
| Electric furnaces | 1.0 |
| Microwaves | 0.90 – 0.98 |
| Electronics | 0.55 – 0.99 |
Resistive loads like incandescent bulbs and electric furnaces use only real power and achieve unity or 1.0 power factor. Reactive motors and ballasted fluorescent lighting have much lower power factors that can be improved with capacitors. Understanding a home’s load mix helps optimize power factor correction.
Power factor correction methods
Here are some common methods used to correct low power factor in residential and commercial buildings:
- Capacitor banks – Banks of capacitors cancel out reactive power from inductive loads
- Synchronous condensers – Rotating motors generating reactive power, less common today
- Passive harmonic filters – Filters out harmonics that increase reactive power
- Active power filters – Advanced electronics to optimize power factor
Capacitors are by far the most cost-effective solution for most small- to medium-sized residential and commercial sites. Strategic placement near motors and other inductive loads improves local power factor. Larger facilities may require active filtering and power conditioning equipment.
Impact of LED lighting on residential power factors
Replacing inefficient incandescent bulbs with LED lighting makes a measurable improvement to whole-house power factors. Some comparisons:
- Incandescent bulbs – power factor 0.95 to 1.0
- CFL bulbs – power factor 0.5 to 0.7
- LED bulbs – power factor 0.9 to 0.99
LEDs maintain excellent power factors close to unity while greatly reducing reactive power versus fluorescent lighting. Upgrading all bulbs in a older home could increase its power factor by 0.05 to 0.1 by itself. LEDs combined with other efficiency improvements can boost power factors over 0.9.
Power factor standards and regulations
Most residential customers are not subject to power factor standards or regulations from utilities. However, commercial and industrial sites may be required to maintain a minimum power factor, such as:
- Minimum 0.9 to 0.95 power factor required
- Penalties may be charged for power factors below standard
- May be incentives or rebates for improving power factor
- Required periodic power factor testing and reporting
Facilities with large concentrated motor loads are commonly targeted for power factor correction standards. By regulating commercial power factors, utilities avoid costs from excess currents and reactive power flows.
Conclusion
The average residential power factor is estimated around 0.85 but can vary from 0.6 up to 0.99 depending on the age, construction, and loads in the home. Older homes with outdated wiring, motors, and appliances tend to have lower power factors. New efficient construction and LED lighting can achieve high 0.9 power factors.
Power factor correction with capacitors is recommended for homes below 0.85 power factor to reduce energy costs. Utilities may also mandate power factor standards for commercial customers to minimize line losses and voltage drops from excessive reactive power. As LEDs replace more lighting loads, average residential power factors will continue to improve over time.