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|HVAC & Water
Home Heating > Energy & Efficiency
Power Options for Central Heaters
Power Options for Space Heaters
|Every type of heater, from the smallest portable unit to the most powerful central system, has to perform work in order to either produce heat (in the case of a furnace or space heater) or transfer heat (in the case of a heat pump). In each case, this work performed by the heating system must rely on some type of power. Correspondingly, this power is provided either by electricity or some type of fuel.|
|Power Options for Central Heaters
In addition to heat source, heat pumps can also be classified based on the type of fuel that they use. The most common type of heat pump, called a “compression” heat pump, runs on electricity. By contrast, an “absorption” heat pump is gas-powered, using either natural gas or liquefied petroleum (LP) gas.
By contrast with heat pumps, there are many more power options that are available with furnaces. In addition to electricity and natural gas, there are furnace models which use oil, propane, or wood. Of these, the most common fuel for residential furnaces is natural gas. This is not surprising, as natural gas is a clean-burning fuel that is both widely available and fairly inexpensive. Propane is another type of gas that is available, but it does not burn as cleanly as natural gas and has a more corrosive effect on various furnace components.
In certain regions, oil-burning furnaces are still quite common. However, in a head-to-head comparison against natural gas, oil tends to underperform. It burns less cleanly, producing additional byproducts. Over time, there is a build-up of sulfur and soot, which must be cleaned out periodically. Even more importantly, oil is both more expensive and less energy efficient than natural gas, making it both a costlier and less effective alternative.
In other regions, wood-burning furnaces are quite popular. Commonly referred to as outdoor wood-fired boilers (OWBs) or simply wood boilers, these are usually built outside and connect to the home through a network of insulated pipes. Such wood boilers have a metal combustion chamber where the wood is burned and the resulting heat is transferred to a surrounding water jacket. The heated water is then distributed through the insulated pipes into the home, where it is used to provide both heating and hot water.
Wood burners can be beneficial relative to traditional gas-powered furnaces in areas where there is an abundance of wood or areas where wood is simply far less expensive than natural gas, oil, or electricity. However, they also require a constant supply of wood and produce smoke emissions which can be unpleasant not only for the residents, but also for the neighbors.
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Power Options for Space Heaters
The most common space heater types are electric-powered and gas-powered. In fact, electricity is such a popular form of power for space heaters that many people refer to them as electric heaters. Technically, however, the term “electric heater” refers specifically to a space heater that is powered by electricity.
Electric heaters offer a number of advantages over their fuel-based counterparts. For one, they provide higher energy efficiencies, as there are no energy losses due to combustion. In addition, electrical heaters do not require venting and are generally safer, minimizing the risk of fire hazard. They are also typically lighter than fuel-burning models. However, electric heaters also have a number of drawbacks. They often cost more to operate and take longer to warm up. Additionally, they require the presence of electrical power, meaning that they are not operable without proximity to a power outlet or during a power outage.
Gas-burning space heaters generally are less expensive to operate than electric heaters and offer greater portability as they are not limited by the need for proximity to a power outlet. In addition, gas-burning space heaters heat up rapidly and can be life savers in the event of an electrical outage during cold weather. On the flip side, gas-burning space heaters tend to cost more, require ventilation, and may not work for particularly small, enclosed spaces. They also tend to be on the noisy side.
Propane-, kerosene-, and wood-burning portable heaters are also available, though they are far less common than electric or gas-burning models. Each of these offers similar advantages to gas-burning space heaters, including power grid independence and a shorter initiation period. Unfortunately, they also share the same drawbacks, including ventilation requirements and a higher risk of fire hazard.
For many consumers, the rule of thumb is to use electric space heaters for indoor spaces and fuel-burning space heaters for outdoor areas. In the case of in-between spaces, such as garages or sheds, either type may work well, depending on the specific layout and the user’s preferences.
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As we have seen, the process of generating heat requires the use of energy, whether in the form of electricity or in the form of fuel. Energy efficiency refers to how effectively that energy is converted to heat by the system, whether that system is a furnace, a heat pump, or a space heater.
There are two arguments in favor of greater energy efficiency, and at least one of them should resonate with most people. The first argument is monetary. A more energy efficient system requires either less electricity or less fuel in order to generate the same amount of heat. In turn, this translates to either a lower utility bill or smaller monthly fuel expenditures. In addition, the government provides tax credits and rebate programs which can put additional money into the consumer’s pocket.
The second argument is environmental. The consumption of both electricity and fuel has a negative impact on the environment because the production of those commodities is generally an environmentally destructive process. A more energy efficient system uses up a smaller quantity of these commodities, thereby reducing the user’s environmental footprint.
The issue of energy efficiency is particularly important when it comes to central heating, as central heating systems generate far more power and, by extension, use much greater resources to maintain their operation. Heat pumps are generally significantly more efficient than furnaces as a result of using a heat transfer process rather than a heat generation process. However, within both the universe of furnaces and the universe of heat pumps there are different energy efficiency levels among disparate systems.
The energy efficiency for a furnace is measured using a metric called the annual fuel utilization efficiency (AFUE). This is a measurement of the system’s efficiency in capturing and utilizing the energy that it draws from its power source over the course of a typical year of operation. The mathematical ratio used to derive the AFUE is heat output divided by total energy consumed. Thus, an AFUE of 90% for a gas-burning furnace means that 90% of the energy available in the natural gas fuel becomes heat for the home, while the other 10% dissipates into the environment. The AFUE only measures the efficiency of the furnace or boiler itself, so any heat losses that occur due to poorly insulated ductwork or piping are not included.
The minimum government-mandated AFUE rating for a furnace is in the 75% to 80% range, depending on the specific type. However, many older, low-efficiency furnace systems have AFUEs that are well below 70% or even 60%. In these cases, it is highly recommended that the old furnace is replaced with a new, higher efficiency model. Modern high-efficiency furnaces can achieve efficiencies as high as 97% or 98%, converting nearly all of the available power to heat for the home. Upgrading to a high-efficiency furnace can not only cut utility bills in half, but also halve the amount of pollution produced by the furnace. For example, replacing an old 56% AFUE furnace with a new 90% AFUE unit in the average cold-climate home will eliminate between 1.5 tons and 2.5 tons of carbon dioxide emissions per year, depending on whether a gas-burning furnace or an oil-burning furnace is used.
Unlike furnaces, heat pumps have a different efficiency rating system. Because heat pumps both heat and cool, they actually have two separate ratings: one for the heating efficiency, and one for the cooling efficiency. The heating efficiency rating is called the heating season performance factor (HSPF) and defined as the total amount of heat providing during the cold season (expressed in British Thermal Units or BTUs) divided by the total amount of electricity used by the heat pump (expressed in watt-hours). The cooling efficiency is called the seasonal energy efficiency ratio (SEER) and defined as the total amount of heat removed during the warm season (expressed in BTUs) divided by the total amount of electricity used by the heat pump (expressed in watt-hours).
As can be seen, the HSPF and SEER are essentially the same measure, except one focuses on the heat provided to the home, while the other focuses on the heat removed from the home. Readers familiar with air conditioning will note that SEER is the same measurement that is used to rate air conditioners. This makes sense as, during the warm season, a heat pump works just like an air conditioner.
The most efficient air-source heat pumps have an HSPF rating of between 8 and 10. Generally, it is recommended that a new heat pump have an HSPF of at least 7.7. A high HSPF rating is particularly important in colder climates. Because a heat pump has to work especially hard when the weather outside is cold, its efficiency is an important determinant of both how effectively it will heat the residence and how much it will accrue in utility expenses.
To attain even greater efficiencies, consumers can utilize geothermal heat pumps. Relative to air-source heat pumps, geothermal heat pumps can provide efficiency improvements of up to 45% while reducing heating bills by 25% to 50% annually. In addition to these benefits, geothermal heat pumps tend to have greater longevity and durability.
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The federal government has introduced a program to help consumers identify the most efficient appliances, not only for heating systems, but for most energy-using products. This program is called ENERGY STAR and it has a two-pronged purpose: “(1) to reduce greenhouse gas emissions and other pollutants caused by the inefficient use of energy; and (2) to make it easy for consumers to identify and purchase energy-efficient products that offer savings on energy bills without sacrificing performance, features, and comfort.”
The ENERGY STAR program is run by the Environmental Protection Agency (EPA). The agency identifies specific products that it deems to be energy efficient and then assigns an ENERGY STAR label to those products. In order to qualify for the ENERGY STAR label, a product must be cost-effective, provide significant energy savings, and deliver the features and performance demanded by consumers. Before the label can be assigned, each product is tested to ensure that it not only works as stipulated, but also delivers the requisite level of energy efficiency.
In addition to identifying products which meet ENERGY STAR’s guidelines, the program also provides tax rebates for consumers who purchase energy efficient heating systems. These rebates allow consumers to recoup a portion of the purchase costs of a new or upgraded heating system. In order to determine whether a particular product qualifies and also to calculate the amount of the possible rebate, you should visit the ENERGY STAR web site at www.energystar.gov.
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