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Learn More About Your Heating System
Steam systems have been around for a long time. Steam heating systems tend to be slower to respond than other types, require more maintenance, and are more temperamental. Consequently, most steam systems have been replaced by other types. However, we still see steam heat in about 2% to 3% of the homes we inspect.
Most remaining steam systems are one-pipe systems. The steam flows from the boiler to the radiator where it gives up its heat and turns back to water (condensate). The condensate flows back by gravity to the boiler to be reheated. The steam goes to the radiator in the same pipe that carries the condensate back to the boiler. The pipes must be pitched back into the boiler for the system to work. The radiators must be pitched toward the supply valves. Sometimes steam radiators lose the proper pitch when the structure of an old house settles and the radiator must be re-pitched to correct this. There are also some two-pipe systems where the steam and condensate are carried in separate pipes to and from the radiator. Large homes may need a vacuum system to get the condensate back to the boiler and the steam to the far reaches of the house.
Venting is very important with steam systems. Most problems with steam systems are due to improper venting. A properly working vent lets air out of the system but keeps the steam in. Radiators closer to the boiler tend to get more steam. This can lead to uneven heating. To counteract this most radiators have variable vents. They can be adjusted so the ones closer to the boiler vent slowly and the ones far away vent quickly. This helps to make the heat more uniform throughout the house.
All steam systems should have a low water cut-off valve. This automatically shuts off the boiler if the water level gets too low. If the boiler were to run with no water in it, it may cause a fire or explosion. The low water cut-off valve must be flushed about every two weeks by the homeowner to prevent dirt build-up which could keep it from working.
Steam systems need water added to them periodically. Most systems have a valve that does this automatically. Some systems have a manual valve, that the homeowner must operate every week or so to keep the proper water level in the boiler. There is a site glass on the side of the boiler so the water level can be monitored.
Steam systems tend to be fussier and require more maintenance than other heating systems. Consequently, very few new homes have steam heating systems.
Hot Water Heating
In a hot water system, a boiler heats water and distributes it through radiators, convectors, fan coils, unit heaters, and sometimes through heat coils in the floor, or in rare occasions, the ceiling (radiant heating). There is an additional hybrid system called “Hydro Air” which will be discussed later.
Boilers are made of steel or cast iron. Steel boilers are less expensive than cast iron and have a design life of approximately 20 years. They heat up faster than cast iron and have less stand-by heat loss. This can result in some fuel economy.
The first generation of boilers were open, unpressurized systems, usually with an open expansion tank having an overflow pipe that was directed to the exterior. These expansion tanks were located in the upper elevation (attic) of the home. Because they were unpressurized they depended on natural convection to move hot water through the distribution system. Although, at the time, this was the state of the art, many of these older systems have been converted to pressurized systems with circulators and expansion tanks. This is a great improvement over the older system, as they tended to be inefficient and slow to respond.
Today our modern heating boilers are very efficient, some obtaining 98% combustion efficiency, eliminating the need for a chimney. Many of our boilers today vent the combustion gasses through the side of the home. These are known as “direct vent” systems.
Most boilers today have the same basic components. They have a burner (gas or oil) that ignites the fuel to produce heat, some method (chimney or direct vent) to expel the combustion gasses, and circulators to move the hot water through the distribution system. In addition, they have controls to keep the system running safely.
There is not much homeowner maintenance required on today’s boilers, but they must be cleaned, including the flue passages, and tuned for peak efficiency annually. This is best left to professionals. The one device that homeowners should be aware of is the “reset” button. This is usually a red button located on or near the burner. If the burner does not fire, this red reset button should be pushed only ONE time. If the burner does not fire after pushing the reset ONCE, call the service technician. Do not continue to push the button. You could cause a fire.
A cast iron boiler works the same as a steel boiler and has the same components. The cast iron boiler costs more but has a longer life span of about 30 years or more.
Forced Air Heating
A furnace heats the air. If you have a hot water system then you have a boiler, not a furnace. The furnace is divided into four major sections. The heat source, the heat exchanger, a fan, and an air filter. The furnace connects to a two-part distribution system consisting of warm air supply ducts and cold air return ducts.
The heat source, commonly a flame fueled by gas or oil, and sometimes electric coils, is contained in the first section of the furnace called the fire chamber. Its configuration is designed to accommodate the type of fuel used. There is an obvious difference between gas and oil fire chambers.
The heat exchanger can be thought of as a sealed container that creates warm air when heated. It is the second section of the furnace, usually above the flame. Its design will vary according to the model of the furnace and the type of fuel. The exhaust gasses are collected from the outside of the heat exchanger and vented to the exterior of the building. With an electric furnace, there are no flue gases, therefore a chimney is not required.
The fan, the third section of the furnace, is the force that circulates the air in the house through the distribution system. It is connected to the cold air return duct, the first part of the distribution system. It sucks cold air from the house and moves it through the furnace where it is heated. The heated air leaves the furnace via the warm air supply ducts, the second part of the distribution system, and delivers through the house.
The filter, the fourth section, is located between the mechanical fan and the cold air return duct. Air sucked out of the house passes through the filter where unwanted particles are removed. The design of the filter will vary according to the homeowner’s needs. They can range from large particle filters to microscopic particle filters. Homeowners need to check the filters every eight to ten weeks and clean or replace them if needed.
The first generations of furnaces were crudely designed. They burned wood or coal as fuel in the fire chamber and had a heat exchanger component. They were installed in the basement. The burning fuel would warm the heat exchanger. The warm air would rise off the top of the furnace and through a large opening on the first floor. The warm air would migrate through the house rising up the stairwell and through openings in the ceilings to the upper floors. Natural convection caused warm air to rise through the house and cold air to drop to the basement. They were not very efficient and responded slowly.
The second generation had supply ducts attached to the top of the furnace. These were usually constructed of sheet metal tubes about eight inches in diameter. They could be routed to each room of the house. The duct system was an improvement but still relied on convection. It was slow and heat distribution was uneven resulting in cold spots and warm spots. This type of furnace is affectionately referred to as “The Octopus Furnace”. The array of ducts stemming off the top of the furnace and spreading out through the basement slightly resembles an octopus.
The fan, filter, and a more efficient duct design were eventually added and the modern furnace came into existence. Many furnaces also have air conditioning systems connected to them.
Heat pumps are used for heating and cooling. Heat pump efficiency is measured in COP (Coefficient Of Performance) the higher the COP, the more efficient the unit.
Heat pumps work just like air conditioning units. They have all the same elements of an air conditioning system: compressor; condenser, evaporator, and expansion device plus two additional features; the reversing valve and the crankcase heater. This allows the heat pump to reverse the refrigerant flow so it can cool in hot weather and heat in cold weather.
Heat pumps do not work as efficiently in low temperatures, say below 25 degrees F to 30 degrees F. The manufacturers have long understood this and incorporate supplemental electric resistance coils in the system to help heat at low temperatures. These electric coils work with the compressor in the “normal” mode to help heat at low temperatures. If you switch to the “emergency” mode, only the electric coils heat and the compressor shuts off. Using the “emergency mode” is an expensive way to heat.
Frost sometimes builds up on the exterior coils in the cold months (around the compressor). This is normal. The heat pump will periodically reverse operations to remove the frost. This is called the defrost cycle. If an excessive amount of ice/frost builds up on the exterior coil there is a problem with the defrost cycle.
Most heat pumps are “air to air”. That is the heat source and delivery are both airs. Some heat pumps use water as the heat source and air as delivery, depending on whether they are heating or cooling. These are water-to-air heat pumps. Usually, they use a pond, groundwater, or a separate well for the heat source.
Like air conditioning systems, heat pumps should be serviced every two years. Homeowners must check the air filters every eight to ten weeks and clean or replace them as needed. This is very important. Dirty filters reduce the system’s performance, increase operating costs and dramatically shorten the compressor design life. Replacing compressors is very expensive.
It is also important to note that the air being delivered to the habitable rooms is at a lower temperature than most people are accustomed to. This is normal with a heat pump.
In order to receive the maximum efficiency from a heat pump system the thermostat should not be moved up or down more than about two degrees Fahrenheit at one time. This allows the compressor to do the work rather than the electric heat coils.
Hydro Air Systems
Hydro-air heating systems use water (hydro) and air to heat. A boiler produces hot water that is sent by a pump through piping to hot water coils in one or more air handling units. The fans in the air handling units pass air over the hot water coils creating warm air to heat the house. Once the water passes through the hot water coil, it cools somewhat and returns to the boiler to be reheated. After the warm air heats the room it cools somewhat and is returned to the air handling unit(s) to be reheated by the hot water coil(s). Hence, the air returned to the air handling unit(s) is called “return air”. The air leaving the air handling unit(s) is called “supply air”.
Although hydro-air heating systems have become popular in the last 10 years or so, they are not new. We inspected a large house built in 1905 that had an original hydro-air heating system. The current heat source was a gas-fired steam boiler. The original boiler was probably coal-fired. There were steam coils in the ducts and air flowed by gravity across the steam coils to gain heat. There were no fans in this system. Consequently, this made the system slow to react and inefficient, but it did work.
Combustion air is the air used in the burning of fuel. Anything that burns fuel uses combustion air. This includes cars, boilers, furnaces, wood stoves, fireplaces, fuel-fired water heaters, and fuel-fired stoves and ovens. Electrically heated devices do not use combustion air.
Using combustion air that comes from outside the house is more energy efficient than using combustion air from inside the house. If your fuel-burning appliances use already heated interior air, it is wasting money.
Insufficient combustion of air can cause a number of problems. Insufficient combustion air causes the appliance to burn incompletely and inefficiently. A properly burning appliance produces very small amounts of carbon monoxide (CO), whereas an improperly burning appliance produces large amounts of carbon monoxide. Carbon monoxide is poisonous. It is also colorless and odorless, so you cannot determine if it is present without special equipment, such as a carbon monoxide detector. Normally, this isn’t a problem as long as the appliance exhaust gases are flowing up the chimney or being properly exhausted from the house. However, if those gases are not being properly vented from the house, it is a potentially deadly situation.
It is very important that boilers, furnaces, wood stoves, and fuel-fired water heaters be serviced regularly by a professional. Oil or wood-fired appliances should be serviced once a year. Gas-fired appliances should be serviced every two years. Normally, gas stoves and ovens do not produce enough carbon monoxide to be of concern.
Electric resistance heat can be a more expensive way to heat a home. However, some builders like to install it due to its low installation cost. It’s a relatively inexpensive installation cost for them but can be a higher monthly operating cost for you. Most homes need a 200 amps electrical service if they have electric heat. Most electric heat is 240 volts.
There are a variety of delivery methods for electric heat: baseboards, fan coils, radiant ceiling panels, and electric furnaces.
Electric baseboards look very much like hot water baseboard heaters. They usually have a thermostat in every room that allows you to shut off the heat for rooms, not in use. It’s important that curtains or electric cords not touch the electric elements inside the baseboards, as they get very hot and could cause a fire.
Electric radiant ceiling panels are an interesting concept. Radiant heat works like the sun’s rays. It heats the objects it hits but does not directly heat the air. When you stand in the sunlight you are feeling radiant heat. All other heating systems heat the room air, directly or indirectly. The theory is that by directly heating people, the room can be kept at a lower temperature while still keeping the occupants comfortable. Theoretically, this saves money over conventional systems, however, studies we have seen indicate people with radiant heat keep their homes at the same temperatures, on average, as those with conventional systems. This usually makes electric radiant heat more expensive to operate than non-electric heating systems. Electric radiant panels are often attached to the concealed side of the ceiling drywall. This means you have to be very careful not to damage them if mounting something or drill through the ceiling.
Electric furnaces work much like gas or oil-fired furnaces except the fuel source is electric. This means electric furnaces don’t require a chimney. Electric furnaces need less maintenance than gas or oil-fired furnaces, nor is there a risk of carbon monoxide poisoning with any electric heat system.