The following pages in Section A of Lesson 8 will cover comparisons of home heating systems.
Home heating systems are classified based on the fuel and/or the method by which the heat is transferred and distributed into the house:
Most newer homes are heated using central heating systems. Those without central heating systems utilize electric baseboard heaters or, in some cases, in-the-wall or in-floor gas heaters or radiant heat.
Instructions: Move your cursor over the numbers below and click to see the characteristics of a central heating system:
Ducted air systems are the most common type of central heating and cooling used. If a home has a central air conditioner, heat pump, or furnace, it is a ducted air system. There are two main types: Forced-air Heating Systems and Gravity Heating Systems.
Almost 35 million homes in America are heated by natural gas-fired, forced-air heating systems- by far the most popular form of central heating.
With a forced-air system, a furnace warms air, an air conditioner cools air, or a heat pump either warms or cools air, then a blower forces the air through the system. Therefore, the same duct system can be used for both heating and cooling.
Below are images of the main components of a forced air heating system. Can you identify each? Drag and drop the image onto its name.
In a forced-air heating system, room air (cooler) is drawn by a fan or a blower through return air registers and ductwork, and passes through a filter (to remove any dust particles) into a furnace, where the air is heated. The warmed air is then blown back to rooms through a system of supply ducts and registers.
Click on the “play” button below to see how a forced-air heating system works.
Click here to open a text description of how a forced-air heating system works
The process begins when cold air is pulled into the return register. The air passes through a filter into the furnace to be heated. The now hot air travels up through the main duct and into the supply branches. Each supply branch has a supply register that allows the hot air to enter the room.
With a gravity furnace, convection currents (caused by the natural tendency of heated air to rise) carry heated air through the system from a furnace that is located on or below the main floor level. Gravity systems, somewhat older, do not have blowers, and tend to have very large air ducts; they can only deliver warmed air.
Press the "play" button below to see how a gravity heating system works.
Click here to open a text description of how a gravity heat system works
In a gravity heating system, a furnace located in the basement heats air that rises and travels to each room, creating a convection current that circulates the warm and cool air.
In gravity heating systems, the ducts are larger than forced-air heating systems, and only warm air travels through them.
Most furnaces are gas-fired, but other fuels include oil, coal, wood, and electricity.
With a conventional furnace, natural gas is piped to a burner located inside a combustion chamber. There, the gas is mixed with air, then ignited by a pilot light, a spark, or a similar device controlled by a thermostat. The flame heats up a metal box—the heat exchanger—where room air is heated as it flows through. Exhaust gases given off by burners vent outside through a flue that goes up through the roof or, with newer high-efficiency models, out through a wall.
Instructions: Press the play button to see how a gas furnace works, and then answer the question that follows.
Click here to open a text description of how a gas furnace works
In a gas furnace, cold air is pulled into the return register and is heated by the heat exchanger; a series of gas burners within a combustion chamber. The hot air is pushed out and distributed through the house. Exhaust from the gas burners exits the building through an exhaust vent.
An electric furnace uses heating elements rather than burners to heat in the heat exchanger.
Instructions: Press the "play" button to see how an electrical furnace works, and then answer the question that follows.
Click here to open a text description of how an electrical furnace works
A motor-driven fan pulls air into the return register. The air passes through a filter and moves past electric heating elements. The now warm air is pushed out the system and distributed throughout the house.
As you may recall from the “drag ‘n drop” activity on the Central Ducted Air Systems page, the main components of a forced-air heating system include the furnace, main duct, branches, and registers.
In a hot-air system, warm air is distributed via a main duct and a series of branches that lead to individual rooms or zones. Where the branches meet the main duct, heat is controlled by dampers (act as valves for air flow), which open or close to release or block heat from entry. These dampers, usually motorized, are run by thermostatic controls at each zone. Individual registers may also be closed to block heat, but this is a less efficient use of the energy and heat produced than when there are thermostatic or automatic controls.
An upward-flow furnace draws cold air in through the bottom and sends heated air out the top. Upward-flow furnaces are often used in houses that have basements or that deliver heat through overhead ductwork.
A downward-flow or counter-flow furnace draws cool return air through the top and delivers heated air out the bottom. This type is favored where there is no basement, or where air ducts are located in the floor.
A forced-air heating system can be combined with air conditioning (for cooling), a humidifier (for maintaining proper moisture balance), and an air filter (for purifying the air). Ductwork is generally metal, wrapped with insulation to help keep heat in. In some cases, flexible insulation-style ductwork is preferred. This system has several advantages and disadvantages, as described below.
In the baseboard hydronic heating systems (shown below), water is heated in a gas-fired or oil-fired furnace located in the basement. The heated water is distributed through pipes into baseboards in various rooms. The heat is then delivered through radiation and convection. Although these are called radiant heating systems, most of the heat delivered is by convection. Heat delivery into rooms or zones can be controlled by flaps or louvers.
A picture of a baseboard heater is shown below. Closely spaced metallic sheets called “fins” increase the surface area for efficient heat transfer into the room.
Advantages | Disadvantages |
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In general, it operates quietly. | Cannot be used for cooling. |
It delivers constant heat and doesn't stir up allergens or dust. | High installation costs. |
Because it warms people and objects rather than just air, it feels warm even if a door is opened or a room is somewhat drafty or slightly cooler than normal. | Interference with furniture placement. |
There is less heat loss (waste) compared to a forced air system because there is no leakage. | Air entrapment can reduce efficiency. |
There are three types of radiant floor heat:
Instructions: Compare conventional baseboard heating to radiant floor heat, by clicking on the button below.
Finish: Comparison of Home Heating Systems [1]
All three types of radiant floor heat (air, electric, hot water) can be further subdivided by the type of installation:
Because air cannot hold large amounts of heat, radiant air floors are not cost-effective in residential applications and are seldom installed.
Electric radiant floors are usually only cost-effective if your electric utility company offers time-of-use rates. Time-of-use rates allow you to “charge” the concrete floor with heat during off-peak hours (approximately 9 p.m. to 6 a.m.). If the floor's thermal mass is large enough, the heat stored in it will keep the house comfortable for eight to ten hours without any further electrical input. This practice saves a considerable number of energy dollars compared to heating at peak electric rates during the day.
Instructions: Press the play button to observe how a concrete floor is charged during time-of-use rates.
Hydronic (liquid) systems, popular and cost-effective systems for heating-dominated climates, have been in extensive use in Europe for decades.
Hydronic radiant floor systems pump heated water from a boiler through tubing laid in a pattern underneath the floor. The temperature in each room is controlled by regulating the flow of hot water through each tubing loop via a system of zoning valves or pumps and thermostats.
Instructions: Press the play button to see how a hydronic radiant floor system works.
Wet installations are the oldest form of modern radiant floor systems. In a wet installation, the tubing is embedded in the concrete foundation slab, or in a lightweight concrete slab on top of a subfloor, or over a previously poured slab.
A new generation of in-floor hydronic heating that employs corrosion-proof, hot-water tubing has enjoyed widespread popularity in recent years. With this type of system, heat is evenly distributed and floors are warm under foot. A variety of heating equipment may heat water: natural gas or propane water heater or boiler, electric boiler, wood boiler, heat pump, solar collector, or even geothermal energy.
Tubing for a hydronic system may be installed in a conventional concrete slab or in a lightweight, gypsum-cement slab. It can also be stapled to the undersides of subflooring as shown in the image below:
A new generation of hydronic heating: This photograph depicts corrosion-proof, hot-water tubing stapled to the underside of subflooring.
Although ceramic tile is the most common floor covering for radiant floor heating, almost any floor covering can be used. However, some perform better than others. Common floor coverings like vinyl and linoleum sheet goods, carpeting, wood, or bare concrete are often specified.
Instructions: Dr. P. is doing some remodeling and needs to purchase new flooring. Assuming his home uses radiant heat, help him select the most appropriate flooring option.
There are various types of tubing used in Radiant floor heating systems.
Instructions: Click on the hot spots in the image below to find out how radiant heat systems are controlled.
Advantages | Disadvantages |
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Radiant floor systems allow even heating throughout the whole floor, not just in localized spots as with wood stoves, hot air systems, and other types of radiators. | Does not respond quickly to temperature settings. |
The room heats from the bottom up, warming the feet and body first. | Relatively expensive to install but can save money in the long run. |
Radiant floor heating also eliminates the draft, dust, and allergen problems associated with forced-air heating systems. | Requires professional installers. |
With radiant floor heating, you may be able to set the thermostat several degrees lower, relative to other types of central heating systems. | |
There are no heat registers or radiators to obstruct furniture arrangements and interior design plans. |
Instead of generating heated air or water at a central location and then distributing it throughout the home, some systems generate heat where it is needed locally. The most common method is electric baseboard heat. Other ways include kerosene heat; wood-burning stoves; and fireplaces burning wood, coal, or natural gas. These systems can heat the whole house, part of the house, or a single room.
Electric resistance heating converts nearly 100 percent of the energy in the electricity to heat. However, most electricity is produced from oil, gas, or coal generators that convert only about 30 percent of the fuel's energy into electricity. Because of electricity's generation and transmission losses, electric heat is often more expensive than heat produced in the home with combustion appliances such as natural gas, propane, and oil furnaces.
Electric resistance heat can be supplied by centralized forced-air furnaces or by zonal heaters in each room, both of which can be composed of a variety of heater types.
Type of Heater | Description | Method of Heating | Installation | Advantages / Disadvantages |
---|---|---|---|---|
Baseboard Heaters | Zonal heaters controlled by thermostats located in each room. Contain electric heating elements encased in metal pipes, which are surrounded by aluminum fins to aid heat transfer and run the length of the baseboard heater's housing, or cabinet. | Convection and radiation. As air within the heater is warmed, it rises into the room, and cooler air is drawn into the bottom of the heater. Some heat is also radiated from the pipe, fins, and housing. |
Usually installed underneath windows where the heater's rising warm air counteracts falling cool air from the cold window glass. Seldom located on interior walls because the standard heating practice is to supply heat at the home's perimeter where the greatest heat loss occurs. Should sit at least three-quarters of an inch (1.9 centimeters) above the floor or carpet, to allow the cooler air on the floor to flow under and through the radiator fins so it can be heated. Should also fit tightly to the wall to prevent the warm air from convecting behind it and streaking the wall with dust particles. |
The quality of baseboard heaters varies considerably. Cheaper models can be noisy and often give poor temperature control. Look for labels from Underwriter's Laboratories (UL) and the National Electrical Manufacturer's Association (NEMA). Compare warranties of the different models you are considering. |
Wall Heaters | Consist of an electric element with a reflector behind it to reflect heat into the room, and usually a fan to move air through the heater. | Convection and radiation. | Usually installed on interior walls because installing them in an exterior wall makes that wall difficult to insulate. | ---------- |
Radiant Heaters | Several types, including electrical heating cables (most common), gypsum ceiling panels and metal radiant panels (provide radiant heat faster than other types because they contain less material to warm up. | Radiation - radiate heat to the room's objects, including its people. For example, you can feel a ceiling-mounted radiant heating panel warming your head and shoulders if you stand underneath it. | Electric heating cables are imbedded in floors or ceilings; gypsum ceiling panels are already equipped with factory-imbedded heating cables; and metal radiant panels are ceiling-mounted. | Offers draft-free heating that is easily zoned. It occupies no interior space, allowing you complete freedom to place furniture without worrying about impeding air flow from registers or baseboard heaters. Manufacturers claim that radiant heat can provide comfort similar to other systems at lower indoor air temperatures, saving around 5 percent of space heating costs. Critics say that it can be difficult to control air temperature with a thermostat. The large heat-storage capacity of the concrete or plaster surrounding the heating cables may result in greater-than-normal fluctuations in the room air temperature, since it takes quite a while to heat up the storage mass. Also, some occupants complain about their heads being too warm in rooms that utilize ceiling radiant heat. Supplying heat at the ceiling or floor, which are locations that typically border the outdoors or unheated spaces, can result in greater heat losses. For example, if there are any flaws in a heated concrete slab or gaps in the ceiling insulation above heating elements, a large percent of the electric heat may escape to the outdoors without ever heating the home. |
Space Heaters | Electric space heaters come in a wide variety of models, either built-in or portable. Portable space heaters, as well as many built-in space heaters for small rooms, have built-in thermostats. Larger rooms heated with built-in electric space heaters should have low-voltage thermostats installed in an area that maintains the room's average temperature. |
These heaters may have fans to circulate heated air, and may also be designed to transfer some of their heat by radiation. | All of these heaters must be given adequate clearance to allow air to circulate safely. | --------------- |
Fireplaces are very commonly used in family rooms and other living areas to give a warm and cozy feeling. These fireplaces can be wood or natural-gas fired.
Generally, fireplaces transfer the heat by radiation, and hot combustion gases (carrying a lot of thermal energy) go out through the stack. Hot gases are lighter and rise up the chimney; a natural suction created by this flow draws the heated warm air from the room.
Most of the time, the warm air heated in the room by the main heating fuel is also drawn into the fireplace and goes up the chimney, resulting in a net loss of energy. It is estimated that about 75 percent of the heated air is lost through the chimney. However, many people still use fireplaces inefficiently.
Click here to open a text description of the fireplace animation.
In rooms heated by a fireplace, warm air from the room is drawn into the fire for combustion. The hot combustion gasses travel up and out the chimney, and heat is radiated from the fireplace throughout the room.
Advantages | Disadvantages |
---|---|
Generates heat at the point of use; no transmission losses. | Heats only certain parts of the home. |
Inexpensive to purchase and install. | Cannot be used for cooling. |
Easy local control in each room. | Takes up living room. |
In well-insulated houses, it may be cheaper than other systems. | Generally less efficient than other central heating systems. |