Feb 22, 2017
The following is a brief discussion or explanation of conventional heating systems in our area. The intention is to answer many of the questions that we field regarding heating systems, and to address misperceptions as they pertain to this important component of a house.
There are four common fuel sources for heating systems in our area, natural gas, propane (LP), heating oil and electricity. By far and away the most common fuel is natural gas. Low pressure natural gas is piped into a house from local utilities (Rochester Gas & Electric, National Fuel Gas, New York State Gas & Electric, etc. ). Your heating system uses natural gas on an as needed basis and the utility company bills the homeowner monthly for the amount of gas that is utilized. Natural gas burns cleanly and is a reliable energy source.
Liquid propane gas is the same fuel that is utilized for most conventional “gas” grills. This is the fuel that is supplied to homeowners in the common metal cylinders that connect to your outdoor grill. Liquid propane is often utilized for heating a house in those areas where natural gas is not available. A propane storage tank would be located on the property. Sometimes these tanks are buried, while other times they are located above ground in a conspicuous location. As is the case with natural gas, propane is pressurized and piped into the house through a system of metal or copper pipes. Propane burning appliances are extremely similar to natural gas burning appliances and operate in much the same manner.
Heating oil is another very common source of fuel in areas where natural gas is not available. Heating oil is a liquid (propane is a liquid when it is pressurized in a tank but it is a gas when it is exposed to the atmosphere). Heating oil is stored in a storage tank on the property, either buried in the ground, on the outside of the house or in a basement. The heating oil is pumped into the burner of the furnace by an oil pump. Heating oil burns quite hot and usually as cleanly as natural gas. Still, it is a very reliable fuel.
For both liquid propane and heating oil the fuel is delivered to the residence by oil suppliers on a periodic basis. The storage tank on the property is filled with fuel and the homeowner is billed for the amount of fuel that is delivered.
At one time it was not uncommon for fuel oil tanks to be buried in the ground. There are certainly advantages to buried tanks since some would consider exposed tanks to be unsightly. However, homeowners should understand that the ownership of a buried tank presents a potential environmental hazard. Leakage from such a tank would result in contaminated soil and the need for environmental cleanup. This is very costly. As a result, buyers of a property that has a buried oil tank should have the tank tested/investigated to ensure that they would not be inheriting an environmental hazard. Buried tanks can be pressure or suction tested, and soil tests can also be conducted to determine if there is existing contaminated soil. For precautionary reasons most buyers chose to have buried tanks removed so that future environmental hazards do not occur.
Electrical heating systems are common in those areas where less expensive municipal electricity is available. For example, Fairport, Churchville and Spencerport have municipal electric companies whose rates are noticeably lower than most large utility companies. In these instances electric heating systems are a very desirable alternative. In most other areas the cost of operation for an electrical heating system makes it undesirable.
TYPES OF HEATING SYSTEMS
Forced Air Furnaces
Forced air furnaces are the most common type of heating systems. There are three major components for a gas or oil fired forced air furnace: the burners, the heat exchanger and the blower. When the thermostat signals the furnace to operate the burners ignite. These burners are positioned inside of the heat exchanger. The heat exchanger is an enclose chamber. Once the heat exchanger heats to a certain set temperature the blower turns on. The purpose of the blower is to suck air from the living space through the return ductwork and into the furnace. This air is forced around the exterior of the heat exchanger by the blower, at which time it is heated and subsequently forced back into the living space through the supply ductwork.
In modern homes the supply grills are usually located at the outer perimeter of each of the rooms and the return grills are located at the interior of each of the major rooms. It is not essential to have a return grill in every room. In some older homes the supplies were located on the interior of the room and the returns were located on the outer perimeter of the rooms. However, over the years, there have been various locations utilized for the supply and return grills (e.g. top of the wall, bottom of the wall, floor, ceiling, interior wall, exterior wall). If you turn the system on, and you feel air coming out of the grill, then it is a supply grill.
As a cost saving measure some budget conscious home builders will place only two or three centrally located large returns in a house. In one way this is undesirable since it does not allow for uniform air circulation through all of the rooms and this can result in larger temperature differences between rooms (e.g. when a bedroom door is closed). This is especially true during the cooling season, since it becomes more difficult to remove hot air from upper rooms of the house and to subsequently distribute cool air evenly throughout the house. The limited number of return air grills usually means that the return air is hard-ducted through the house, rather than using the wall cavities for return air. This can be more effective from a “system efficiency” perspective, but it does not provide uniform temperatures in the various rooms.
For air conditioning purposes, it is desirable for each major room to have a return grill located at a higher elevation in the room. However, in a retrofit situation with an existing house that only has two or three return air grills, the cost of adding upper wall or additional return air grills is usually not cost effective.
The by-products of combustion from inside of the heat exchanger are exhausted or vented out of the furnace through a vent pipe or vent connector. For safety reasons it is very important for these by-products to exhaust to the exterior. In most conventional homes the vent connector is connected to a chimney or vent stack that runs up through the house and terminates above the roof. It is important for the vent connector and the chimney or vent stack to be intact so that all of these “fumes” are exhausted to the exterior.
Modern high efficiency or “ninety plus” furnaces are vented with PVC or “plastic” pipe. Because of the high efficiency of these furnaces they can be vented directly out the side wall of a house, rather than into a chimney. These types of furnaces will reduce energy costs, but they are more costly to purchase and install.
The heat exchanger is the central and most critical part of a forced air furnace. Cracks, holes or openings in the heat exchanger can result in an unsafe condition since the by-products of combustion can escape into the house, rather than being vented to the exterior. For this reason, regular maintenance on a furnace should include a thorough investigation or evaluation of the heat exchanger. Protocol dictates that if there is a crack, fracture, hole or breach in the heat exchanger the furnace is potentially unsafe. For furnaces that are not very old the heat exchanger can be replaced. For older furnaces it becomes justified to replace the furnace if the heat exchanger is defective.
We would caution homeowners that some heating contractors in the interest of selling a new furnace might try to wrongly indicate the presence of a defective heat exchanger. You should always obtain a number of opinions prior to replacing your furnace for this reason.
Some of the advantages of forced air furnaces are that they are relatively inexpensive to install, they supply reliable efficient heat, the duct system allows for easy installation of a central air conditioning system, the system can be retrofitted with a central air humidifier, air cleaners and filters can be easily installed, etc.
On the downside, forced air heat can be relatively drafty since it causes movement of air, and it also tends to create more noticeable fluctuations in indoor air temperature as the system cycles on and off. Electric forced air furnaces operate in a very similar fashion to that of gas or oil fired furnaces. The difference is that the heat source consists of large electric coils. There is no burning or combustion. Essentially, the electric coils are very similar to the inside of your toaster, but obviously on a much bigger scale. As is the case with a gas furnace, room temperature air is drawn into the furnace through the return ductwork by a blower, and then the air is heated as it passes over the hot electric coils. The air is then sent back into the interior rooms through the supply ductwork. Electric furnaces are very reliable and there tends to be less maintenance associated with these furnaces. However, unless you are fortunate enough to live in an area where electricity is inexpensive, an electric furnace is more costly to operate.
Hot Water Boilers
Hot water heating systems are also relatively common in this area, but they are greatly out numbered by forced air heating systems. The heart of the hot water system is the boiler. The boiler heats the water in the system. This hot water is then circulated throughout the house via a system of pipes and either radiators or baseboard heaters (some old systems do not use a pump, but rely on gravity). Cast iron radiators are normally found in older homes with hot water systems. The temperature of the water circulating through the radiators is usually approximately 160 degrees Fahrenheit. Radiators become noticeably warm as a result of the hot water flowing through them, and they subsequently radiate heat into the living spaces of the house.
Most modern hot water systems utilize fin tube baseboard heating devices. These baseboard units look quite similar to an electric baseboard heater. However, the hot water from the boiler is fed through the baseboard unit, resulting in radiation of heat. These systems are normally operated at higher water temperatures (upwards of 180 degrees Fahrenheit or more). Radiant heat in the floor or ceiling is sometimes utilized in a house since these heat supplies do not have to use radiators or baseboard heating units.
Hot water systems are low pressure systems. They normally operate at a water pressure of less than 20psi.
Hot water heating systems provide a very reliable form of heat. These systems also provide a more comfortable and uniform heat since they do not move air throughout the house. Also, even after the boiler shuts off, the radiators or baseboard units continue to slowly radiate heat into the room for some period of time until the water within them cools off. As a result, there tends to be less noticeable fluctuations in indoor temperature.
Another significant advantage to hot water heating systems is that the house can be more easily split into “zones”. A zone is a section of the house that is heated independently from the other areas of the house. The heat in each zone is separately controlled by its own thermostat. This can allow a homeowner to regulate the temperature in their bedrooms differently than in the living room or kitchen. As an example, for a typical two story colonial house with a single story modern addition at the rear of the first floor the hot water heating system can be designed so that there are three heating zones, one for the second floor “bedrooms”, one for the first floor of the main house, and a third for the rear addition. Leaving certain zones at a lower set temperature means that the system does not have to work as hard to heat the entire house, and this results in energy savings.
Zoned heating is possible with forced air systems, but they are somewhat more complex and they rely on the operation of thermostatically controlled vent dampers. These systems are somewhat rare, and they are typically found in large modern upscale homes.
The disadvantages of a hot water heating system is that it provides heat and heat alone. Any humidification, air filtering or air conditioning would have to be provided by completely separate systems. In the case of wanting an air conditioning system it would be necessary to install a complete system of ductwork to air condition the entire house. Hot water heating systems tend to be more costly to install. Boilers can be more expensive, and the associated piping for the system is more expensive. Hot water boilers can be fueled by natural gas, heating oil or propane. There are electric boilers in existence, but these are rare.
Another advantage to hot water heating systems is that there can be a separate zone from the boiler that is utilized to heat the domestic water supply for the house. This eliminates the need for a separate water heater. Instead, hot water from the boiler is fed into a tank that contains heating coils. As the hot water from the boiler circulates through the tank it heats the hot water supply for the spigots in the house.
Steam boilers are less common than hot water boilers in homes, but they are scattered around the Rochester area. They too can be fueled by natural gas, heating oil or propane. As their name implies, these boilers produce steam rather than hot water. The steam is distributed throughout the house via a system of pipes and radiators. Similar to hot water radiators, steam radiators heat due to the presence of the hot steam inside of them. Eventually the steam condenses to water and returns to the boiler where it is reheated.
Steam boilers look very similar to hot water boilers. However, hot water boilers are usually equipped with circulation pumps, and the system is equipped with an expansion tank. These pumps serve to circulate the heated water through the system. Steam boilers in homes do not have expansion tanks, and usually do not have pumps. Instead, you will typically find a glass sight tube on the side of a steam boiler. This is a narrow vertical glass tube that is partially filled with water. It indicates the level of water in the system.
Natural gas, propane and oil forced air furnaces will provide an average life expectancy of approximately twenty years. If maintained properly they can sometimes last much longer than twenty years. Electric forced air furnaces can also provide twenty or more years of dependable use.
Hot water and steam boilers will usually last even longer than furnaces. Thirty plus years of serviceable life can be achieved if the boilers are maintained properly (up to 50 years is not uncommon).
Heat systems should be cleaned and serviced on an annual basis as a sensible preventative maintenance measure and as a safety precaution. For forced air systems it should include a thorough evaluation of the heat exchanger. Some homeowners have purchased maintenance plans from heating contractors. In this case homeowners pay an annual fee to the contractor in return for performance of routine maintenance. Warranties are often provided with these agreements. You can check with your heating contractor for further information in this regard.
WHEN TO REPLACE YOUR HEATING SYSTEM
Obviously, a heating system will need to be replaced when it is old, unsafe for use and/or when it fails. Eventually a heating system will require repairs that are more costly than what would be justified for a heating system of its age. In other words, it would not make sense to spend $1200.00 to repair a twenty year old furnace if it could be replaced for $2000.00.
Homeowners should be cautioned that although some contractors will try to sell new heating systems based strictly on energy efficiency, it can be somewhat difficult to justify the cost of replacing a furnace or a boiler with only the intention of saving money on heating bills. We’ve even seen or heard advertisements from heating contractors claiming if your furnace is more than twelve years old it is inefficient and it should be replaced. Most modern furnaces and heating systems are more efficient, but the cost of replacing the system can greatly negate the anticipated gains in efficiency and subsequent reduction in fuel bills. We would strongly urge any homeowner to thoroughly investigate the anticipated savings prior to replacing a furnace or boiler for only reasons of fuel savings.
Many furnaces that remain in use today are older “natural draft” furnaces. These furnaces are relatively inefficient by today’s standards. Their efficiency is less than 80 percent. Since they are relatively inefficient the by-products of combustion or vent gases tend to be quite warm. These vent gases naturally rise out of the heat exchanger into the vent connector and subsequently into a chimney or vent stack. Modern furnaces are more efficient resulting in vent gases that are much cooler. What this means is that when an old natural draft furnace is replaced with a modern furnace it is often times the case that the chimney that was utilized to vent the furnace needs to be modified or relined to accommodate differences in efficiency between the old furnace and the new furnace. This adds to the cost of furnace replacement, and it should not be ignored. Avoiding relining of a chimney when a modern furnace is installed can eventually result in improper operation of the heating device and deterioration of the interior of the chimney. Your heating contractor can provide details regarding venting modifications that would be necessary when the heating system is replaced.
This discussion on heating systems would be incomplete without including a few words about heat pumps. Heat pumps are air conditioning devices that can also operate in reverse. In other words, they provide both cooling and heating. In the summer a heat pump operates exactly as a typical air conditioner. In the cooling mode the unit on the exterior of the house is the compressor and condenser. This equipment is connected to a coil that is mounted on a furnace/air handler/duct system inside of the house via a pair or refrigerant pipes. The coil on the interior of the house is an evaporator coil. This coil becomes very cold during the cooling cycle. When air is pulled into the system via the return ductwork it passes over this cold evaporator coil, cooling the air that is subsequently sent back into the living space via the supply ductwork.
During the air conditioning cycle the temperature of the cooled air is as much as twenty degrees Fahrenheit lower than the temperature of the air in the house. In other words an air conditioning system that is operating in a house whose indoor air temperature is 75 degrees should produce cooled air between 55 and 60 degrees.
During the heating cycle the heat pump reverses its operation. The indoor coil becomes a condensing coil and the exterior coil becomes an evaporator coil. As a result, the indoor coil now becomes quite hot so that the air that passes through the system is heated by the condensing coil. During the heating cycle the temperature gain for the air in the system can be as much as 30 degrees. Therefore, if a heat pump is used to heat a house whose indoor air temperature is 70 degrees the heated air being sent to the supply grills can be approximately 100 degrees.
Heat pumps can provide reliable heat assuming that outdoor air temperatures are not too cold. Heat pumps can not efficiently heat a house once the exterior air temperature is below 35 or 40 degrees. Obviously, below freezing temperatures are realized quite often in the Rochester area. As a result, there is always a second means of heat in a house that is equipped with a heat pump.
Heat pumps are also electric devices. This means that heat pumps are not desirable heat sources unless they are located in an area with inexpensive electric rates. This is why heat pumps are often times seen in Fairport and Spencerport, but rarely in areas that are served by Rochester Gas & Electric, Niagara Mohawk, New York State Gas & Electric, etc.
A heat pump is generally used as the first source of heat. Once the heat pump cannot adequately heat the house, the second heat source begins to operate. This second form of heat is oftentimes an electric furnace, but heat pumps can also be utilized in conjunction with gas or oil furnaces. The transition or switch between a heat pump and a secondary furnace occurs automatically in order to adequately heat the house. However, when temperatures are below approximately 35 degrees, the system will try to continue to use the heat pump, even though the second heat source might be the less costly one to use, in terms of energy use. When temperatures will be consistently below 35 degrees, homeowners may want to set their thermostats to “EM. HEAT” to bypass the heat pump operation altogether. Before re-energizing the heat pump, the system should be set to “HEAT” for several minutes (perhaps 15 minutes or more) prior to allowing the system to actually call for heat, to allow heaters in the outdoor heat pump unit to warm the system prior to operation.
Since heat pumps only produce air of approximately 100 degrees homeowners often times will comment that they tend to create drafts or that they do not provide a generous amount of heat. In contrast, a typical furnace can provide heated air of approximately 125 to 130 degrees. However, an electric heat pump is less expensive to operate than an electric furnace.
We hope that this summary of heating systems provides you with some general understanding of the conventional types of heating systems, fuel sources and heating maintenance. Please do not hesitate to contact our office if you have any questions regarding this topic or others.