Chicago HVAC News

A properly maintained heating system is likely to work better and last longer. It can also save your life: Malfunctioning systems increase the risk of carbon-monoxide (CO) poisoning and cause some 6,000 fires and $47 million in property damage each year, according to the Consumer Product Safety Commission.

The best time to check your system is before you turn it on. Simple steps include changing or cleaning furnace filters and dusting heat registers or baseboard radiators. Older systems might require blower-motor or water-pump lubrication. Replace batteries in digital thermostats and CO alarms and smoke alarms. Then hire a pro for an annual checkup.

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A maze of heating and air conditioning ducts runs inside the walls and floors of 80 percent of American homes. As the supply ducts blow air into the rooms, return ducts inhale airborne dust and suck it back into the blower. Add moisture to this mixture and you’ve got a breeding ground for allergy-inducing molds, mites and bacteria. Many filters commonly used today can’t keep dust and debris from streaming into the air and over time sizable accumulations can form — think dust bunnies, but bigger.

To find out if your ducts need cleaning, pull off some supply and return registers and take a look. If a new furnace is being installed, you should probably invest in a duct cleaning at the same time, because chances are the new blower will be more powerful than the old one and will stir up a lot of dust. Professional duct cleaners tout such benefits as cleaner indoor air, longer equipment life and lower energy costs. Clean HVAC systems can also perform more efficiently, which may decrease energy costs, and last longer, reducing the need for costly replacement or repairs. Cleaning has little effect on air quality, primarily because most indoor dust drifts in from the outdoors. But it does get rid of the stuff that mold and bacteria grow on, and that means less of it gets airborne, a boon to allergy sufferers.

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Most houses with forced-air furnaces have a standard furnace filter made from loosely woven spun-glass fibers designed to keep it and its ductwork clean. Unfortunately, they don’t improve indoor air quality. That takes a media filter, which sits in between the main return duct and the blower cabinet. Made of a deeply pleated, paper-like material, media filters are at least seven times better than a standard filter at removing dust and other particles. An upgrade to a pleated media filter will cleanse the air of everything from insecticide dust to flu viruses.

Compressed, media filters are usually no wider than six inches, but the pleated material can cover up to 75 square feet when stretched out. This increased area of filtration accounts for the filter’s long life, which can exceed two years. The only drawback to a media filter is its tight weave, which can restrict a furnace’s ability to blow air through the house. To insure a steady, strong airflow through the house, choose a filter that matches your blower’s capacity.

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A neglected in-duct humidifier can breed mildew and bacteria, not to mention add too much moisture to a house. A common mistake with humidifiers is leaving them on after the heating season ends. Don’t forget to pull the plug, shut the water valve and drain the unit. A unit with a water reservoir should be drained and cleaned with white vinegar, a mix of one part chlorine bleach to eight parts water or muriatic acid. Mist-type humidifiers also require regular cleaning to remove mineral deposits.

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Tuning up the distribution side of a forced-air system starts with the blower. The axle should be lubricated; blades cleaned and lower motor checked to insure the unit isn’t being overloaded. The fan belt should be adjusted so it deflects no more than an inch when pressed. Every accessible joint in the ductwork should be sealed with mastic or UL-approved duct tapes. Any ducts that run outside the heated space should be insulated. On a hot-water system, the expansion tank should be drained, the circulating pump cleaned and lubricated and air bled out of the radiators.

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Heat pumps and oil-fired furnaces and boilers need a yearly professional tune-up. Gas-fired equipment burns cleaner; it should be serviced every other year.

Step 1
A close inspection will uncover leaks, soot, rust, rot, corroded electrical contacts and frayed wires. In furnace (forced-air) and boiler (hot-water) systems, the inspection should also cover the chimney, ductwork or pipes, dampers or valves, blower or pump, registers or radiators, the fuel line and the gas meter or oil tank, as well as every part of the furnace or boiler itself.

Step 2
Next, the system should be run through a full heating cycle to ensure that it has plenty of combustion air and chimney draft. Contractors use smoke pencils to check for sufficient draft and also test the air for carbon monoxide.

Step 3
Finally, it’s time for the down and dirty task of cleaning the burner and heat exchanger to remove soot and other gunk that can impede smooth operation. For the burner, efficiency hinges on adjusting the flame to the right size and color, adjusting the flow of gas or changing the fuel filter in an oil-fired system. A check of the heat pump should include an inspection of the compressor, fan, indoor and outdoor coils and refrigerant lines. Indoor and outdoor coils should be cleaned, and the refrigerant pressure should be checked. Low pressure indicates a leak; to locate it, contractors feed tinted refrigerant into the loop and go over it with an electronic detector.

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Hot water and steam systems work similarly, but neither are typically installed in newer homes. However, because both are still in existing homes, here are some maintenance tips for them.

Because water retains heat, it is used to store and distribute heat in home systems. There are two types of hot water systems: the gravity system and the hydronic or forced hot water type. Hot water heating systems can be powered by gas, oil, or electricity. Gravity systems depend on the upward flow of hot water to circulate heated water from the boiler through a system of pipes to radiators in the rooms of your home. The better radiators for hot water systems are called convectors. These units employ a series of fans to disperse the heat.

The heat from the water in the radiators or convectors is transferred first to the metal radiators and then to the air. As the water loses its heat, it sinks and flows back to the boiler through return pipes. Most gravity systems heat the water to no more than about 180 degrees Farenheit, and cooled water that goes back to the boiler rarely falls below 120 degrees Farenheit.

Hydronic hot water systems use a motor-driven pump to move the hot water.

Open gravity systems have an overflow outlet to let water escape; this prevents a buildup of excess pressure in the system. Closed systems have a sealed expansion tank; when water pressure builds up in the system, the excess water flows into the expansion tank to prevent damage to the pipes or the boiler. Hydronic hot water systems are much like closed gravity systems, except a hydronic system uses a motor-driven circulating pump to move the water. As a result, water in a hydronic system moves more rapidly and arrives at the room radiator with less heat loss than water in a gravity system.

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It’s important to replace the filters and clean and lubricate the components of a heat pump on a regular basis. But heat pumps, like central air conditioners, have an outdoor unit that contains a compressor, a coil, a fan, and other components. To function properly, this unit should be kept free of debris such as leaves and dirt. The unit should be level on its concrete support pad.

Clean pine needles, leaves, and dirt out of updraft fans by removing the grille, which is held to the frame by a series of retaining screws. Make sure the power to the unit is off before tackling this type of cleaning. A vacuum cleaner hose can sometimes be inserted between the fan blades to remove debris from the sides and bottom of the unit.At the beginning of each heating season, set a carpenters’ level across the top of the metal cabinet and check the level from side to side and from front to back. If the unit is no longer level on the pad, lift the pad back to level by prying it up with a pry bar or a piece of 2-by-4. Build up the ground under it with stone or crushed rock. Also check the piping insulation for deterioration. If this insulation is faulty, replace it with new insulation, available at heating supply stores. Installation instructions are usually provided by the manufacturer.

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A heat pump not only heats your home during the winter, it also cools it during the summer. It does not burn fuel to produce heat nor does the electricity it consumes go through an element. The heat pump functions on the same principle as refrigerators and air conditioners: A liquid absorbs heat as it turns into a gas and releases heat as it returns to a liquid state.

During the summer, the heat pump operates as a standard central air conditioner: It removes heat from the house and vents it to the outside. A liquid refrigerant is pumped through an evaporator coil of tubing. The liquid expands as it moves through the coil, changing to its gaseous state as it absorbs heat from the air surrounding the coil.A blower then pushes air around the cooled coil through ducts and into the house. The gas, now carrying considerable heat, moves through a compressor and begins the liquefying process. It then moves to a condensor coil outside the house, where the compressed gas releases its heat and returns to a liquid state.

During the winter, the heat pump reverses this process, extracting heat from the cold air outside and releasing it inside the house. The heat pump is very efficient when the outside temperature is around 45 degrees Farenheit to 50 degrees Farenheit, but it becomes less efficient as the temperature drops. When the outside air temperature is very low, an auxilery electric heater must be used to supplement the heat pump’s output.

Like standard electric heating systems, this auxilery unit is more expensive to operate. Thus, in areas where the winter temperature is below freezing, a heat pump is not practical. It has few advantages over conventional heating systems in areas where air conditioning is not necessary, but it is very efficient in warm to hot climates.

Heat pump maintenance is important. Small problems that are not addressed early can lead to very expensive compressor problems later. And since maintaining a heat pump is more technical than caring for the average heating system, you should call a professional service person when the pump malfunctions. You can, however, keep the system free of dirt by keeping the filter clean and by removing any other obstacles to the flow of air.

Proper outdoor maintenance of a heat pump is also important.

Fueled by gas, electricity, or oil, a forced-air distribution system is just what the name implies. Air is forced from the furnace through ducts to registers in various rooms. Besides warming the air, the blower system that distributes the warmed air also returns the cold air to the furnace so it can be rewarmed and distributed to the rooms again.

A forced-air system is also efficient for distributing cool air from a central air conditioner with the same ducts, registers, and blower. There is little that can go wrong with a forced-air system. The big problems typically include noise and blockage of airflow, usually caused by dirt or by furniture or draperies blocking the registers. Forced-air systems should be cleaned and maintained regularly. Floor registers are slip-fit into ducts or are held by retaining screws on the frame of the register. Wall and ceiling registers are also held in place by retaining screws on the frame of the register. Duct joints are usually slip-fit and held with sheet-metal screws or duct tape. The ducts are supported by wire or metal strap hangers nailed or screwed to wooden framing members such as studs and rafters. All of these parts are easy to disassemble. Lay them out in order as you work so you’ll be able to reassemble them properly.

A problem can arise with this type of system in which the temperature of different rooms varies widely.

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Although an electric heating system does have advantages, its operating cost generally makes it less desirable than any of the other furnace systems available today. The high cost means that minimizing heat loss caused by improperly installed ducts or inadequate insulation is even more important than with other types of systems.
For maximum energy efficiency, have a professional service person clean and adjust your electric furnace every year before the beginning of the heating season. Do not attempt any repairs to the heating elements, electrical connections, relays, transformers, or similar components of an electric furnace; repairs to these components must be made by a professional service person.
The controls of an electric furnace may be mounted on the surface of the housing or installed behind an access panel on the front of the furnace. The access panel may be slip-fit on hooks fastened to the furnace housing with a series of sheet-metal screws. To remove the access panel to the blower, filter, and blower motor, slip the panel up off hooks or remove a series of sheet-metal screws.

Fuses

Electric furnaces are fused at a building’s main electrical service entrance. Many electric furnaces are on separate circuits, sometimes located in a separate fuse box away from the main panel. The heating elements of the furnace are also fused, and these fuses are located on a panel that is on or inside the furnace housing.

If changing the fuses or resetting the breakers does not restore power to the furnace, call a professional service person. Do not attempt to repair heating elements, the transformer, heating relays, or power relays. Repairs to these components must be made by a professional service person.

Now that we’ve run the entire furnace gamut, your home should be nice and toasty all winter long. Though major furnace repairs to a furnace are best left to a professional, you should be able keep those house calls to a minimum with our maintenance tips.

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Oil-fired burners are used in many parts of the country as the basic heat source for warm air and hot water heating systems. Most of the home oil systems in use today are called pressure burners. In this type of system, oil is sprayed into a combustion chamber at high pressure, propelled by a blower, and ignited by an electric spark.

The oil continues to burn as the mist is sprayed. While there aren’t many quick fixes you can undertake yourself on these types of furnaces, good regular maintenance can help eliminate many problems. Here are a few oil furnace maintenance tips:
Oil Furnace Care Guide
From annoying noise to low heat, there are many problems that can strike your oil furnace. Click here for instructions on how to deal with specific issues.

* During the heating season, check the smoke from the chimney. If the smoke is black, the furnace is not burning the oil completely and fuel is being wasted. Call a professional service person for adjustments.

* Clean the blower at the beginning of the heating season and again about midway through the season.

* Clean soot from the stack control about midway through the heating season.

* If the blower motor has grease or oil fittings, lubricate the fittings midway through the heating season with cup grease or 10-weight nondetergent motor oil (not all-purpose oil), available at hardware stores.

* Clean the thermostat before each heating season.

Most oil furnaces in use today are called pressure burners.
© 2006 Publications International, Ltd.
Most oil furnaces in use today are called pressure burners. In this type of system,
oil is sprayed into a combustion chamber at high pressure.

An oil furnace is a complex assembly. The maintenance and repair work for this type of furnace is limited to simple parts: the filters, the blower, the motor belts, the switches, and the thermostat. Electrodes, an oil nozzle, air tubes, a transformer, a pump, and other components require special tools and testing equipment and are best left to a professional for service.

To become familiar with your oil furnace, remove the access panel covering the burner blower by removing the retaining screws around the rim of the housing. You can access the air blower and filter through a metal panel on one side of the furnace. The panel is held by either hooks or retaining bolts; slip the panel up and off the hooks or remove the bolts and lift the panel off. Most furnaces have switches and reset buttons located on the motor or in a switch box outside the furnace housing. These are usually identified with stampings or labels, such as DISCONNECT SWITCH, RESET, and so on. The stack control sensor, a safety device that monitors burner operation, is positioned in the stack and held with a series of retaining bolts.

What You’ll Need
You’ll want to have these tools on hand to check the oil filter:

* Wrench
* Screwdriver
* Replacement filter and gaskets

Oil Filters

The oil filter should be changed or cleaned at the start of the heating season and about midway through the season. Here’s how to clean or replace the filter:

Step 1: Close oil shutoff valve between fuel tank and filter.

Step 2: Unscrew bottom or cup of filter housing, and remove filter.

Step 3: If filter is disposable, insert new one of same size and type. If furnace has permanent filter, clean filter according to furnace manufacturer’s recommendations.

Step 4: Replace old filter gaskets with new ones.

Step 5: Screw in bottom of housing, and open oil shutoff valve.

Clean the pump strainer after cleaning the oil filter.
© 2006 Publications International, Ltd.
Clean the pump strainer after cleaning the oil filter. To reach the strainer,
unbolt the cover of the pump housing and lift off the cover.
Some oil furnaces have a pump strainer, which is located on the pump attached to the burner/ blower unit. Clean this strainer when you clean the oil filter. Here’s how:

Step 1: Unbolt cover of pump housing (where oil line enters burner), and lift off cover.

Step 2: Remove thin gasket around rim. Find and remove strainer, which is a cylindrical or cup-shape wire mesh screen.

What You’ll Need
You’ll want to have these tools on hand to clean the pump strainer:

* Wrench
* Kerosene
* Old, soft toothbrush
* Replacement pump strainer and gasket

Step 3: Soak strainer in kerosene for several minutes to loosen any built-up sludge. Carefully clean strainer with old, soft toothbrush.

Step 4: Inspect strainer. If it’s torn or badly bent, replace it with new pump strainer of the same type.

Step 5: Set strainer into place on pump, place new gasket on rim, and bolt cover of pump housing back on.

Switches

Some oil furnaces have two master switches. One is located near the burner unit, and the other is near the furnace housing or even at a distance from the furnace. Make sure these master switches are both turned to the ON position.

Stack Control

The stack control of the oil furnace, located in the stack, is a safety device that monitors the operation of the oil burner. If the burner fails to ignite, the stack control shuts off the motor. Frequently, however, a furnace shutdown is caused by a malfunctioning stack control rather than by the burner.

What You’ll Need
You’ll want to have these tools on hand to check the stack control:

* Wrench
* Brush
* Soapy water
* Soft cloth
* Newspaper
* Refractory cement

If the burner fails to ignite, first check the fuel tank and refill it if necessary. If the tank doesn’t need to be refilled, press the reset button on the stack control. If the burner doesn’t ignite after you’ve pressed the button once, clean the control, as detailed below. Then press the reset button again. If the burner still doesn’t operate, call a professional service person.

The stack control gradually becomes coated with soot during the heating season. To keep it working properly, clean the control every month or as soon as it becomes soot-covered. Here’s how to clean the stack control:

Step 1: Remove bolts that hold control in stack. Pull out sensor and its housing.

Step 2: With brush dipped in soapy water, remove all soot from control. Wipe control dry with soft cloth.

Step 3: Before replacing control, clean stack. Spread newspaper to protect floor, then disassemble stack. As you work, remove soot and debris from each section by tapping them firmly on newspaper-covered floor.

Step 4: After cleaning sections, reassemble them in reverse order. Make sure stack sections are properly aligned and firmly connected.

Step 5: Finally, reposition stack control in stack, and reseal connection to chimney with refractory cement.

To remove the stack control, turn off the power to the furnace, then back out the bolts.
© 2006 Publications International, Ltd.
Clean the stack control every month. To remove the control, turn off the power
to the furnace, then back out the bolts that hold it in the stack.
Some oil furnaces have an electric-eye safety switch instead of a stack control. This switch serves the same function as the stack control. If the burner has an electric-eye safety, remove the access cover over the photocell; it is held by hooks or retaining screws. Wipe the cover clean to remove accumulated soot. Reassemble the switch, replace the cover, and turn the power back on. If the burner still doesn’t ignite, call a professional service person.

If the stack control or electric-eye safety switch is especially dirty, the furnace may not be properly set to burn the fuel completely. In this case, call a professional service person for adjustment.
Caution: Do not attempt to replace these controls yourself.

Draft Regulator

The draft regulator, located on the stack, is closed when the burner is off but opens automatically to let air into the chimney when the burner is turned on. Accumulated soot and rattling are signs that the draft regulator needs to be adjusted. Too much air in the chimney wastes heat; too little air wastes fuel by failing to burn it completely. To increase the airflow, screw the counterweight inward. To decrease airflow, turn the counterweight outward. The draft regulator should be adjusted by a professional service person as part of regular annual maintenance.

Limit Switch

The limit switch is a safety control switch and is located on the furnace just below the plenum. If the plenum gets too hot, the limit switch shuts off the burner. It also shuts off the blower when the temperature drops to a certain level after the burner has shut off. If the blower runs continuously, either the blower control on the thermostat has been set to the ON position, or the limit control switch needs adjustment.

To determine the problem, check the thermostat. If the blower control has been set to ON, change it to AUTO; if blower control is already on AUTO, the limit switch needs adjusting. To do this, remove the control’s cover and find the toothed dial underneath. One side is marked LIMIT; don’t touch this side. The other side is marked FAN. There are two pointers on the fan side; the blower turns on at the upper pointer setting and shuts off at the lower pointer setting. Pointers should be set about 25 degrees apart. Set the upper pointer at about 115 degrees Fahrenheit and the lower one at about 90 degrees Fahrenheit.

Burner Adjustment

Do not try to adjust the burner of an oil furnace; call a professional service person.

Finally, we have electric furnaces and heaters. Electric heat is in some ways much simpler than either gas or oil, but it can still have its fair share of problems.

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Natural gas and propane burn cleaner than fuel oil, and most gas furnaces present fewer operational difficulties than oil burners do. In fact, the problems that affect gas furnaces typically involve the furnace’s thermocouple, the pilot light, or some component of the electrical system.

Gas furnaces and heaters have control shutoffs to prevent gas leaks, but they are not fail-safe. If you smell gas in your house, do not turn any lights on or off, and do not try to shut off the gas leading to the furnace. Get out of the house, leaving the door open, and immediately call the gas company or the fire department to report a leak. Do not re-enter your home.On some gas furnaces and heaters, a plug-type door covers the pilot light assembly. To gain access to the pilot burner, pull the door out of the furnace housing. On other units, remove the panel that covers the pilot and gas burners.

The pilot light controls, reset buttons, gas valves, and thermocouple are usually contained in an assembly at the front of the furnace. The furnace limit switch is located on the plenum (main chamber) or main duct junction on the upper housing of the furnace.

What You’ll Need
You’ll want to have these tools on hand to check the pilot light:

* Matches
* Fine wire

The Pilot Light

The pilot light on a gas furnace can go out because of drafts. To relight the pilot, follow the manufacturer’s instructions exactly; they are usually fastened to the furnace. If instructions for relighting the pilot are not provided, follow this general procedure:

Step 1: Find pilot light assembly. It typically has a gas valve with on, off, and pilot settings.

Step 2: Turn valve to off and wait three minutes.

Step 3: Switch valve to pilot setting. Hold lighted match to pilot opening while you push reset button on pilot control panel. Keep this button depressed until pilot flame burns brightly, then set valve to on position.

Step 4: If pilot flame won’t stay lit, opening may be clogged. Turn gas valve off, and clean opening with piece of fine wire. If it won’t stay lit after several attempts, you may have faulty thermocouple. If pilot flame still won’t stay lit, call professional service person.

Some furnaces have an electrical system to ignite the gas; in these systems there is no pilot light. Instead, an electric element heats up and ignites the burners. If this electric ignition system malfunctions, call a professional service person.

Replacing the Thermocouple

The thermocouple is a gas furnace component located near the pilot light burner. It is a safety device that shuts off the gas if the pilot light goes out or the electric igniter fails.

If the pilot light won’t stay lit, the thermocouple may be faulty and should be adjusted or replaced. To adjust the thermocouple, you must tighten the thermocouple nut with a wrench. Take care not to apply too much pressure to the nut — just tighten it slightly. Then try lighting the pilot. If the pilot won’t stay lit, replace the thermocouple with a new one of the same type. Here’s how to replace a thermocouple:

What You’ll Need
You’ll want to have these tools on hand to replace a thermocouple:

* Wrench
* Replacement thermocouple

Step 1: Unscrew copper lead and connection nut inside threaded connection to gas line. Under mounting bracket at thermocouple tube, unscrew bracket nut that holds tube in place.

Step 2: Insert new thermocouple into hole in bracket. Be sure steel tube is up and copper lead is down. Under bracket, screw bracket nut over tube. Push connection nut to threaded connection where copper lead connects to gas line. Make sure connection is clean and dry.

Step 3: Tightly screw nut into place, but do not over-tighten. Both bracket nut and connection nut should be only a little tighter than if hand-tightened.

The thermocouple is installed next to the pilot light on a gas furnace.
© 2006 Publications International, Ltd.
The thermocouple is installed next to the pilot light. A bracket holds
it in place, steel tube up and copper lead down.
Limit Switch

The limit switch is a safety control switch located on the furnace just below the plenum. If the plenum gets too hot, the limit switch shuts off the burner. It also shuts off the blower when the temperature drops to a certain level after the burner has shut off. If the blower runs continuously, either the blower control on the thermostat has been set to the ON position or the limit control switch needs adjustment. Check the thermostat first. If the blower control has been set to ON, change it to AUTO; if the blower control is already on AUTO, the limit switch needs adjusting.

Gas Furnace
Care Guide
There are a myriad of problems that can cause your gas furnace to malfunction. Click here for instructions on how to deal with specific issues.
To adjust the switch, remove the control’s cover. Under it is a toothed dial with one side marked LIMIT; don’t touch this side. The other side of the control is marked FAN. There are two pointers on the fan side; the blower goes on at the upper pointer setting and turns off at the lower pointer setting. The pointers should be set about 25 degrees apart. Set the upper pointer at about 115 degrees Fahrenheit and the lower one at about 90 degrees Fahrenheit.

Burner Adjustment

The flames on the gas burner should be full and steady, with no sputtering and no trace of yellow. To adjust the flame height on the main burners, call a professional service person. To adjust the height of the pilot flame, turn the flame adjustment screw until the flame is from 11/2 to 2 inches high. The adjustment screw is located near the gas valve on the pilot assembly, if the control has this adjustment feature.

Gas Leaks

If you suspect leaks around the furnace unit, stir up a mixture of liquid detergent and water. Paint this mixture on the gas supply line along its connections and valves; the soapy water will bubble at any point where there’s a leak. If you find a leak, try tightening the leaking connection with a pipe wrench, but be careful not to overtighten the connection. If the pipe connections or valves still leak, call a professional service person.

An oil furnace has an entire new set of the problems from the ones we’ve just conquered in gas furnaces.

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Heating systems are usually trouble-free and easy to maintain. Efficient operation is a function of good regular maintenance. No matter what type of furnace you have, there are several things you can do to keep your heating system in top condition. In this article, we will tell you how to service and troubleshoot your furnace, regardless of the type. Before we get to the troubleshooting, let’s start with some steps you can take before your furnace shuts down. Cleaning a Furnace

Dirt is the biggest enemy of your furnace. It can waste fuel and drastically lower efficiency. Dirt affects all three basic components of your furnace, so cleaning is the most important part of regular maintenance. The three parts of the furnace should be cleaned: the filter system, the blower, and the motor.

The furnace filter should be replaced or cleaned at the beginning of the heating season and about once a month during periods of continuous use. To check the filter, take it out and hold it up to the light. If it looks clogged, replace it with a new filter of the same type and size regardless of the length of time it has been used.

What You’ll Need
You’ll want to have these tools on hand to clean a furnace filter:

* Screwdriver
* Replacement filter
* Toothbrush
* Vacuum cleaner
* Clean rags

A disposable furnace filter consists of a fiber mesh in a cardboard frame. The size of the filter is printed on the edge of the frame. An arrow on the edge of the frame indicates the correct direction of airflow through the filter. Air flows from the return-air duct toward the blower, so the arrow on the filter should point away from the return-air duct and toward the blower.

A permanent filter is usually sprayed with a special filter-coating chemical, available at hardware stores and home centers. Clean this type of filter according to the manufacturer’s instructions, which are usually attached to the furnace housing. Here’s how to replace a filter:

Step 1: Look for metal panel on front of furnace below return-air duct, between duct and blower system. Panel may be marked filter, or it may form lid or front of boxlike projection on furnace housing.

Step 2: Slip panel off its holding hooks, or unscrew panel from box or furnace housing. On some heating units, filters are exposed; just slip filter up and out of U-shape tracks that hold it in place.

Three parts of the air-moving system should be kept clean: filter, blower, and blower motor.

Step 3: Inspect and replace or clean filter, depending on type.

Step 4: Clean blower assembly, belts and pulleys to blower, and motor housing. Cleaning blower is critical if furnace has a squirrel-cage fan, because openings in this type of blower often become clogged with dirt. To clean blower, remove panel that covers filter to gain access to blower or panel on front of furnace. This panel may be slip-fit on hooks or held by series of retaining screws. Access to inside of blower is usually gained by sliding out fan unit, which is held on track by screws.

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The thermostat, a heat-sensitive switch, is the basic control that regulates the temperature of your home.

It responds to changes in the temperature of the air where it is located and turns the furnace or air conditioner on or off as needed to maintain the temperature at a set level, called the set point. The key component of the thermostat is a bimetallic element that expands or contracts as the temperature increases or decreases in a house.Older thermostats have two exposed contacts. As the temperature drops, a bimetallic strip bends, making first one electrical contact and then another. The system is fully activated when the second contact closes, turning on the heating system and the anticipator on the thermostat. The anticipator heats the bimetallic element, causing it to bend and break the second electrical contact. The first contact is not yet broken, however, and the heater keeps running until the temperature rises above the setting on the thermostat.

More modern thermostats have coiled bimetallic strip elements, and the contacts are sealed behind glass to protect them from dirt. As the temperature drops, the bimetallic elements start to uncoil. The force exerted by the uncoiling of the elements separates a stationary steel bar from a magnet at the end of the coil. The magnet comes down close to the glass-enclosed contact, pulls up on the contact arm inside the tube, and causes the contacts to close, completing the electrical circuit and turning on the heater and the anticipator. As the air in the room heats up, the coil starts to rewind and breaks the hold of the magnet on the contact arm. The arm drops, breaks the circuit, and turns off the system. As this point, the magnet moves back up to the stationary bar, keeping the contacts open and the heater turned off until the room cools down again.

The latest heat and air-conditioning controls use solid-state electronics for controlling the air temperature. They are typically more accurate and more responsive than older systems. However, repair to solid-state controls usually means replacement.

Understanding how the heating and cooling systems function in your home will help you head off problems before they become too serious.

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Most of us take heating and cooling for granted. We expect our heating systems to keep us warm during the winter, and we depend on air-conditioning to keep us cool during the summer.

When the house is cold in winter or hot in summer, the natural reaction is to call for professional service. Fortunately, there is an alternative. You can cut service costs drastically and keep your heating and cooling systems working efficiently by doing some maintenance and quick fixes yourself. But first, it’s important to know how the basics of how heating and cooling systems function.How Heating and Cooling Systems Work

All climate-control devices or systems have three basic components: a source of warmed or cooled air, a means of distributing the air to the rooms being heated or cooled, and a control used to regulate the system (e.g., thermostat). The sources of warm air, such as a furnace, and cool air, such as an air conditioner, in a house often use the same distribution and control systems. If your house has central air conditioning, cool air probably flows through the same ducts that heat does and is regulated by the same thermostat. When a heating or cooling system malfunctions, any of these three basic components may be causing the problem.

Both heating and air conditioning work on the principle that heat always moves from a warm object to a cooler one, just as water flows from a higher to a lower level. Furnaces and heaters put heat into the air to make your home warmer; air conditioners remove heat to make your home cooler.

All heating and cooling units burn fuel. Air conditioners use electricity. Most home heating systems use gas or fuel oil; other systems use electricity. The heat pump — an electrically powered climate control unit — both heats and cools air. In summer it extracts heat from the air inside your home. In winter it pulls heat from the air outside and uses this heat to warm the air inside.

When the furnace is turned on, it consumes the fuel that powers it, whether it be gas, oil, or electricity. As fuel is burned, heat is produced and channeled to the living areas of your home through ducts, pipes, or wires and then is blown out of registers, radiators, or heating panels. Older systems use the heat they produce to heat water, which in turn heats the air in your home. These systems use a boiler to store and heat the water supply, which is then circulated as hot water through pipes embedded in the wall, floor, or ceiling.

When an air conditioner is turned on, electrical power is used to cool a gas in a coil to its liquid state. Warm air in your home is cooled by contact with the cooling coil, and this cooled air is channeled to the rooms of your home through ducts and out registers or — in the case of room air conditioners — directly from the unit itself.

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