Heat Pump vs. Furnace – Comparing the Two OptionsPublished on: October 8, 2013
In most American households, heating is provided by one of two types of HVAC systems: a heat pump or a furnace. Both types of heating systems are effective and reliable. However, furnaces and heat pumps have distinct differences and characteristics that should be given careful consideration before making a purchasing decision. Here is a comparative buying guide for heat pumps and furnaces, with explanations of the advantages and disadvantages of each system. Use this information to help guide your search for the best and most efficient heating equipment for your area.
Heat Pump vs. Furnace: Choosing and Sizing
Choosing a new heat pump or furnace requires evaluation of several factors that can have a strong effect on how well the system works. The equipment you choose must be able to produce the amount of heating you need on a consistent and reliable basis. Choosing “just any old unit” will not bring you good results. In cooperation with your local trusted HVAC contractor, you should make every effort to install a furnace or heat pump that is properly sized and has all the features you need.
Proper sizing of both a furnace and a heat pump employs a process intended to determine exactly how much heating your home requires and how much capacity is required in the system that will produce the heat. The first step in sizing a home heating system is usually a heating load calculation. The “load” is the amount of heating you need to keep your indoor environment at the temperature you prefer. A load calculation is a sophisticated process that evaluates structural and thermal characteristics of your home and determines how much heating will be necessary. With this information in hand, your HVAC supplier can help you choose a heat pump or furnace that is big enough and powerful enough to generate enough heat.
Heating load calculations should be performed by qualified professionals using the standards and procedures in industry-accepted sources, such as Manual J “Residential Load Calculation,” published by the Air Conditioning Contractors of America (ACCA).
Heat Pump vs. Furnace: Fuel and Power Types
The type of fuel and power options you have available is a major consideration for your purchase. Furnaces generally use two different energy sources, either fossil fuels that are burned to produce heat, or electricity that generates heat with internal heating elements. The types of fuels burned in furnaces include natural gas, fuel oil and propane.
- In most urban areas, homes are already hooked up to natural gas lines to enable a furnace connection. If you don’t have a connection available but the lines pass your home, you’ll have to contact the utility company to have a tap-in installed.
- Homeowners who live outside the range of utility supply networks often opt for fuel oil or propane, which typically is stored in a tank just outside the home. Supplies of these fuels must be monitored and maintained to ensure you don’t run out of fuel at the most inopportune time.
- A large amount of these fuels must be purchased at one time when you have the tank refilled. In contrast, natural gas is delivered continually and is billed monthly.
- Some types of fuels, such as natural gas and propane, do present a small safety risk. If mishandled, these volatile substances could cause a fire or explosion, though these cases are rare.
- Fuel-based furnaces also present the risk of carbon monoxide exposure. Carbon monoxide is a byproduct of the combustion process that produces heat. Exposure to this odorless, colorless and tasteless gas can harm health and even cause death. Fuel-burning furnaces require extra attention to regular maintenance, proper operation and correct venting, along with the installation of carbon monoxide detectors.
- Furnaces are usually individual self-contained units.
In comparison, heat pumps:
- Are powered by electricity, so they do not require any sort of utility connection beyond standard residential electrical power.
- Produce no carbon monoxide and present no danger of fuel ignition or explosion.
- Usually consist of an indoor unit and an outdoor unit. The functions of each depend on whether the heat pump is providing heating or cooling.
Heat Pump vs. Furnace: System Operation
Furnaces operate by a relatively simple process that detects the temperature inside your home and turns the furnace off and on in response to temperature changes. When the thermostat senses that indoor temperatures have fallen below the unit’s settings, it switches the furnace on. The burners ignite or the heating elements activate and produce heat. When enough heat is produced, the air-handling fan blows the warm air into the ductwork system and out at vents placed throughout your home. The air warms your home, and when its heat energy is expended, a return-air system brings air back to be filtered, heated and distributed again. This process continues until the thermostat detects a rise in temperature to the set level, then shuts off the furnace. When temperatures fall, the process begins again.
In contrast, heat pumps provide heating and cooling functions by capturing and moving heat from place to place. This is accomplished by using a liquid/gaseous refrigerant in a series of copper pipes called coils. The heat pump contains a set of coils in the indoor unit and another in the outdoor unit. When the system is providing heating, the refrigerant in the outdoor coils is evaporated into a gas, which absorbs heat. The gas moves into the indoor unit, where it is condensed back into its liquid form. As it condenses, it releases the heat indoors. The heat is then distributed by the indoor air handling unit. When the heat pump is providing cooling, the process is reversed, with heat being captured indoors and released outdoors.
Heat Pump vs. Furnace: Efficiency
Both heat pumps and furnaces can provide high levels of efficiency, but in general (but not always), heat pumps are more efficient and economical than either fuel-based or electric furnaces.
Furnace efficiency is measured by the system’s Annual Fuel Utilization Efficiency (AFUE) number, which indicates the percentage of energy in the fuel that is turned into usable heat when the fuel is burned. Many newer furnaces have relatively high AFUE ratings of 90 percent or more. An AFUE of 90 means that 90 percent of the energy in the fuel becomes heat, while the other 10 percent is lost. The higher efficiency rating, the better the furnace performs and the less it costs to operate. New fossil-fuel warm-air furnaces must have an AFUE of at least 78 percent. High-efficiency models will have an AFUE of 90 percent or higher. Electric furnaces generally have AFUE ratings of 95 or higher, though the cost of electricity to power these systems is typically higher than natural gas.
In contrast, heat pump efficiency is measured by its HSPF, or Heating Seasonal Performance Factor. HSPF ratings range from the minimum required of 7.7 for units manufactured after 2005 to 9.35. A heat pump with an HSPF of 8.2 is considered a high-efficiency model.
Furnace efficiency can be boosted by the addition of components designed to make the unit more efficient, such as:
- Variable-speed air handlers: These air handlers are designed to operate at different speeds depending on the amount of heating required to meet temperature settings. When less heat is needed, they run at a lower speed, which saves energy and money. Their near continuous, usually low-level operation saves on energy, and provides more event heating and better air filtration. It’s also easier on system components than a standard blower motor.
- Electronic ignitions: Many older fuel-burning furnaces use a pilot light that consumes fuel to keep it running. Newer units with electronic ignitions do not require a pilot light. These ignition systems produce a spark that lights fuel when heating is needed.
- Dual heat exchangers: Some furnaces have two heat exchangers for acquiring usable heat. The second heat exchanger is designed to pull additional heat out of the system’s exhaust gases, recovering heat energy that otherwise would be wasted.
Heat pumps also have optional features that can increase their efficiency. They include:
- Variable-speed compressors: Dual-speed compressors run at two different speeds, depending on the amount of heating or cooling required. When they run at their lower levels, they use less energy and cost less to operate.
- Two-stage thermostats: These thermostats improve efficiency by controlling when the unit’s electric coils activate to produce heat. They ensure the heat pump’s standard heat-moving system is activated first and that the electric coils are turned on only if required.
Heat Pump vs. Furnace: Influences of Climate
In general, a furnace is appropriate for use in any climate, no matter how cold the winters get. Heat pumps, however, tend to lose efficiency when outdoor temperatures fall below freezing point. Many units have backup heating coils that generate heat when temperatures reach these levels. When the heating system switches to the coils, the energy and monetary benefits of the heat pump are negated, and costs to run the unit increase dramatically. For this reason, standard air-source heat pumps are not recommended for geographical areas where temperatures frequently fall below freezing and stay there for extended periods. This is the case unless they’re paired with a backup furnace in a dual-fuel system. Dual-fuel systems will switch over to the gas burner when temperatures get very cold, but also give homeowners the option to use the furnace when natural gas prices are especially low.
Your local HVAC professional can provide all the information and services you need to decide between a heat pump and a furnace. Contact AC Southeast today for help finding heating contractors in your Southeast U.S. community who sell, install, and service both heat pumps and furnaces.