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Information for Renters

76 Expert Q&A

Q. What is an R-Value?

Posted on August 2012

A. Materials vary enormously in their ability to conduct heat. Those that do not conduct it well are called insulators. R-Value is the term used to indicate a material’s resistance to heat flow or ability to insulate; therefore, the higher the R-Value, the better the insulator. Most insulation materials work by trapping pockets of air, which is an excellent insulator. Fiberglass does this by creating air pockets between spun glass fibers, and foam insulation contains air bubbles. Similarly, double- and triple-pane windows work by trapping air or a slow-moving, low-conductive, dense gas between the panes.

Among insulating materials, R-Values can vary widely. This is the reason it is important to purchase insulation by the R-Value and not by the inch. R-Values of different materials can be compared while thickness cannot. For instance, two materials rated R-11 have precisely the same insulating ability while two inches of each may not. Take fiberglass and brick as an example. To achieve R-30 with fiberglass batts requires 8.5 inches, while it would take 60 inches of brick.


A. Surge protectors degrade over time. This is because the majority of surge protectors rely on a metal oxide varistor, or MOV, to work. MOVs only conduct electricity if and when the power level reaches an excessive level. That excess power is rerouted automatically to the ground wire, which safely dissipates the excess electricity into the ground. But over time, MOVs degrade. That’s why it’s good to buy a model with a failure indicator. And some models come with an automatic cutoff or auto shut-off safeguard. These models cut off power to the surge protector if and when the MOV has degraded to the point where it can no longer adequately protect any connected equipment.

Q. What is COP?

Posted on August 2012

A. The most common heat pump efficiency measurement is called the Coefficient of Performance, or COP. COP is the ratio of the heat pump’s BTU (British Thermal Unit) heat output to the BTU electrical input. Conventional electric resistance heaters have a COP of 1.0. This means it takes one watt of electricity to deliver the heat equivalent of one watt.

Air-source heat pumps generally have COPs ranging from 2 to 4; they deliver two to four times more energy than they consume. Water and ground source heat pumps normally have COPs somewhere between 3 and 5.

The COP of air-source heat pumps decrease as the outside temperature drops. Therefore, two COP ratings are usually given for a system: one at 47°F and the other at 17°F. When comparing COPs, make sure ratings are based on the same outside air temperature.

COPs for ground- and water-source heat pumps don’t vary as much because ground and water temperatures are more constant than air temperatures.

While comparing COPs is helpful, it doesn’t tell the whole story. When the outside temperature drops below 40°F, the outdoor coils of a heat pump must be defrosted periodically. It’s actually possible for the outdoor coil temperature to be below freezing when a heat pump is in the heating cycle.

Under these conditions, any moisture in the air will freeze on the surface of the cold coil. Eventually the frost could build up enough to keep air from passing over the coil and the coil would then lose efficiency. When the coil efficiency is reduced enough to appreciably affect system capacity, the frost must be eliminated. To defrost the coils, the heat pump reverses its cycle and moves heat from the house to the outdoor coil to melt the ice. This reduces the average COP significantly.

Some units have an energy saving feature that will allow the unit to defrost only when necessary. Others will go into a defrost cycle at set intervals whenever the unit is in the heating mode.

Q. What is EER?

Posted on August 2012

A. The cooling efficiency measurement for heat pumps is the Energy Efficiency Ratio or EER. This is the same rating system used for air conditioners.

EER is the number of BTUs (British Thermal Units) of cooling provided per watt of electrical energy consumed. The energy includes electricity used for indoor and outdoor fans and the compressor. Although similar to COP (Coefficient of Performance), EER is calculated using different units of measure.

EER ratings higher than 13 are the most desirable.

COP and EER measurements are based on laboratory tests and do not necessarily measure how the heat pump performs in real life. A heat pump’s performance will vary depending on the weather and how much supplementary heat is actually required. Therefore, a more realistic measurement, especially for air-to-air heat pumps, is calculated on a seasonal basis that would include cooling and heating. This efficiency measure is the Heating Season Performance Factor (HSPF) for the heating cycle and the Seasonal Energy Efficiency Ratio (SEER) for the cooling cycle.

Q. What is electrical grounding?

Posted on August 2012

A. A good ground connection is essential to the safe, reliable operation of any piece of electrical equipment in the home. Electrical grounding ensures that if there is ever a short on a piece of electrical equipment, current will flow through the ground system and trip a breaker or blow a fuse, thereby providing protection from injury or electrocution. Grounding also is the primary path through which a surge protector dissipates energy from an electrical spike. A ground system’s ability to dissipate electricity is measured in ohms. The NEC (National Electric Code) Article 250 calls for a ground system of 25 ohms or less with 0 ohms being the unattainable but theoretical “perfect ground.” Properly installed ground rods achieve the 25 ohm requirement.

Equally important is that all wires and pipes entering the house be bonded to a single ground point. This means the electrical, cable TV, water and telephone phone systems should all be connected with electrical conductors.

Separate ground rods for phone or cable, that are not connected to the electrical ground rod are unsafe and probably a violation of the local electrical code.

If you have a ground rod installed, be sure it tests to less than 25 ohms. If you have a ground rod and the cable or phone lines are not bonded to it, call Georgia Power today to check your system.

Q. What is ENERGY STAR®?

Posted on August 2012

A. A joint program of the U.S. Department of Energy (DOE) and the U.S. Environmental Protection Agency (EPA), ENERGY STAR® is designed to help everyone save money while protecting the environment through energy-efficient practices and products. According to the DOE, “Americans, with the help of ENERGY STAR®, saved enough energy in 2010 alone to avoid greenhouse gas emissions equivalent to those from 33 million cars—all while saving nearly $18 billion on their utility bills.”

Q. What is HSPF?

Posted on August 2012

A. The Heating Season Performance Factor, or HSPF, can be thought of as the “average COP” for an entire heating season. HSPF is calculated by taking the total annual heating requirements, including all energy inputs (defrost and back-up heating energy included) divided by the total electric power used.

The industry standard rating system compares BTUs (British Thermal Units) of heat output to watts of electrical energy input. Since there are 3.4 BTUs per watt of electricity, an HSPF of 7.7 corresponds roughly with an average COP of 2.3. An HSPF of 7.7 or greater is required by the code.

Q. What is insulation?

Posted on August 2012

A. Insulation is any material that restricts heat flow. It comes in a wide variety of materials, including mineral, organic, fibrous, and reflective, and in many forms, such as batts, blankets, loose fill, rigid and foam. Insulation is installed in homes to reduce heat flow through the home’s envelope, keeping heat in during winter and out in summer. Considering that in most parts of the country, almost half of the home’s energy dollar goes to heating and cooling, improvements to the envelope are often good investments. Even though insulation materials themselves do not use energy, or heat or cool, they have a big impact on home energy bills and comfort.

If you currently have little or no insulation and you have already sealed air leaks with caulk or weatherstrip, adding insulation may be the most cost-effective energy improvement you can make. However, adding insulation to an existing home can be difficult and fairly expensive, so take time to evaluate your home carefully, learn a little about insulation and get advice and estimates from experts. An in-home energy audit may help you prioritize measures.

Q. What is renewable energy?

Posted on August 2012

A. Renewable energy is energy harnessed from or generated by naturally replenishing resources, such as sunlight, wind, rain, tides and geothermal heat.

Q. What is SEER?

Posted on August 2012

A. The Seasonal Energy Efficiency Ratio, or SEER, is the total cooling of the heat pump in BTUs (British Thermal Units) divided by the total electrical energy input in watt-hours during the same period. Naturally, the SEER for a unit will vary depending on where in the country it is located. A SEER of 13 or greater is required by the Department of Energy (DOE).


76 Expert Q&A