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 Draft Fan Inducer and Vent
In this photo you can see how the draft fan inducer motor relates to the furnace vent. If your furnace has a chimney vent and motor right under it, then you do not have a condensing furnace but rather an induced draft furnace.
Gas furnace intermittent pilot gas valve system pictures and images.
The following image describe Lennox furnace with an Intermittent pilot system using a Mercury flame sensor instead on an electronic system using flame rectification. Note the high voltage lead on the pilot burner. If this was a standing pilot system there would be a thermocouple where the flame sensor is.
Note the label on the fan/limit telling you to set the heat anticipator to .5 amps (500MA)
Over all view of system. This furnace uses a conventional fan control as opposed to one that uses an electronic control. The wires at the base of the gas valve are part of the pilot valve system. The terminals at the top are the main valve. If you are having problems with your main burner going off when it shouldn't or suspect a bad valve, connect a test lamp or meter here. On THIS SYSTEM the fan would start on its own without the gas burner firing.
 Conventional fan limit control (this one has an assist heater) with cover removed. One that does not have an assist heater looks almost the same except there are no wires in the center. This one is made by Honeywell, one made by White-Rodgers or Roberts haw look all most the same.
Some controls have a manual push button to operate the fan manually.
Furnace service, repairs and efficiency improvement
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There are many inquires about problems with the pilots on gas furnaces. Unless you have a newer furnace with an electronic or electric ignition system you probably have a standing pilot. That is a system where the pilot is always burning and is used to light the main burner. There are two basic systems used with standing pilots. The first is the thermocouple system that uses two dissimilar metals to provide electricity to hold open the pilot valve on the gas valve, once you light the pilot. The main valve is operated by 24 volts from a transformer.
The thermocouple is relatively generic. There are some versions that put out slightly more voltage than others and have a longer life rating. However, the ones that you buy at the home stores should work fine.
Image of standard standing pilot gas valve
Notice pilot tube connection on left side of valve and thermocouple connection in center of valve. Only standing pilot systems have a pilot position on the valve knob (you must push to light the pilot).
If you have an electronic (intermittent pilot) system The valve will have the designations MV MV/PV PV (main valve pilot valve and common) and no connection for a thermocouple. Hot surface ignition/direct spark valves will not have a pilot tube connection.
Image of standard standing pilot thermocouple (available at Lowes or The Home Depot)
Notice the connection on the end is the same as the connection on the gas valve to the left. This device is used on all standing pilot systems including water heaters and commercial gas equipment except Millivolt or some General Electric furnaces they have a special gas valve that has a pilot gas output but no thermocouple connection just a main valve (proven pilot). If you need to replace one of these turds, replace it with a standing pilot valve or an intermittent kit.
The second system is called a Millivolt system. The pilot heats a larger device that generates a bit more electricity, enough to operate the main valve too. The theory is that if the pilot is not lit then the main burner won't work and you don't need a 24 volt transformer. This system is used a lot on mobile home, RV furnaces and swimming pool heaters because they will work with out utility power.
If you have problems where the pilot won't stay lit after you release the button or knob then replaces the thermocouple. If you still can't get the flame to stay try another thermocouple then replace the gas valve (sorry there is nothing else that can be done). The problem is not with your thermostat or the furnace transformer. Note: the thermocouple has nothing to do with the main valve opening so don't replace your thermocouple if the pilot is already lit.
The exception is on some old furnaces they have a box with the thermocouple and a rest button for the main burner (usually made by Penn Basso).
Image of Millivolt Thermo-pile, the wire ends give it away for sure. If you need to replace one of these my personal preference is to convert it to a standard standing pilot 24 volt system.
Newer furnaces will have intermittent pilot, hot surface ignition (HSI) or direct spark. The intermittent system uses a gray control box made by Honeywell, Roberts haw, Johnson controls, Fen wall, or White-Rodgers to spark the pilot and detect that it is lit, these boxes are very reliable but when they fail you are looking at least $100 for the box.
Another system is called cycle pilot. The pilot is lit by a pilot re-light module and a mercury flame sensor allows the main valve to open. This same module can be added to a furnace that has a nuisance pilot that blows out frequently.
Proven pilot has a mercury sensor in the flame to allow the main valve to open (used on general electric).
Hot surface igniters are being used more and more today. The major advantage is the controls are cheaper. They just need a flame sensor to detect the main burner and open the main valve. The problem with them is the igniter burns out and you are cold until you can get another one. When they fail you can either replace the igniter or convert the sensor board to direct spark. If the sensor board fails I would just convert it to single wire direct spark, that way you eliminate future problems with the igniter (you need a different one for every brand of furnace). To test an ignitor connects a 120 volt bulb (about 25 watts) in its place or use a multi-meter. If you get 120 volts but the igniter doesn't glow then it is bad. When replacing it be careful not to touch it with your fingers. Oil on you skin can shorten its life.
Standing pilot is the most reliable and fool proof but intermittent, HSI or direct spark is good for situations where lighting the pilot is a nuisance and property damage could result.
Image of hot surface ignition (HSI)
This one is broken.
It is a good idea to get a few of these and keep them near the furnace so when they burn out on the coldest day of the year when it is snowing you will have a spare. Some new systems like Loch Invar boilers use this device as the flame sensor (isn't that sneaky)
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Central Air Conditioner and Heat Pump Maintenance
The condensing unit of a central air conditioner or heat pump resides outside throughout the year and needs at least annual attention just as any other aspect of your home's Heating, Ventilating and Air Conditioning (HVAC) system.
Annual maintenance should include:
• Cleaning dirt, leaves and other debris from the condensing coils
• Checking condensing coil fins for damage
• Lubrication of fan bearings
• Inspection of fan for damage
Let's review how to maintain a central air conditioner or heat pump condensing unit:
Shutting Off Power to the Unit
Shutting off the power to the condensing unit will involve locating what's called an electrical disconnect switch and turning off the 240 volt power at that point. The disconnect is a weatherproof metal box located near the condensing unit.
To turn the power off proceed as follows:
• Open the disconnect switch box and depending on its design, remove the power plug which activates the box, or turn off the power with the shutoff handle or remove the fuse plug.
• Also turn off the power to the unit at the main electrical service panel.
• Wait a few minutes before proceeding with any further maintenance steps. This will allow any stored electrical charge that may reside in the unit's capacitors to dissipate.
Remove Protective Grilles and Lubricate Motor
To access the outside and inside of the condenser coil you must remove the protective side grille. You also need to remove the top panel that protects the fan, motor and interior of the condensing unit.
To remove the grille proceed as follows:
• Remove the screws holding the side and top panels in place using a Phillips head, flat blade screwdriver or socket driver as required and place the screws in a secure area.
• With care, pull the side grill away from the unit and lift the top panel which may also support the fan motor.
• Carefully support the top grille with the motor and fan making sure not to stress any electrical wiring connections.
• Locate the fan motor oil ports above the fan blade and place a few drops of lightweight household oil into each port.
Clean Condenser Coils
Cleaning the coils of debris is the first step. When cleaning the coil fins, be careful not to bend them. You'll be cleaning the coil from the outside and the inside. Once the power is shut off proceed as follows:
• Clean the outside of the coil of any sticks or debris.
• Vacuum the outside of the coil fins using a soft bristle brush attachment. You do not want to bend the fins when vacuuming.
• Once the outside is relatively cleaned, turn your attention to the inside of the condensing unit. Using a hose with a spray gun, spray water from the inside of the coils through to the outside of the coils which will remove stuck debris.
• Do not spray the fan motor or wires.
• Vacuum out or remove by hand, any debris that is littering the inside bottom of the unit.
• If your unit has no bent coil fins, then replace the grille covers. If your unit has bent fins, then proceed to the next step.
Straighten Bent Coil Fins
If your condensing unit has coils that are bent, they should be straightened out as much as possible for proper performance of the unit. You cannot straighten the fins properly without a special tool called a fin comb. These tools come in a variety of styles including single, multiple or interchangeable heads having different fin comb sizes and counts to best match the coil fin size of the repaired unit. Some six sided head models will work for 8, 9, 10, 12, 14 and 15 fins per inch coils.
• To straighten the bent fins, match the teeth count of the comb to the fins per inch of the coil. Then carefully draw the comb across the bent coil fins straightening them out in the process.
• Replace the grille covers and screws.
Making Sure the Condenser Unit is Level
The condenser must be level for proper operation. If it is not, then problems with drainage and premature wear and tear will occur. To check for level, proceed as follows:
• Take a level and lay it on the top of the condensing unit in north/south and east/west orientations.
• The unit should be level in both orientations.
• If it is not, adjust the height and level the unit by adjusting the leveling feet or by shimming the feet with wood shims slightly to achieve level.
• If the unit is seriously out of level, then repair or replace the concrete slab block the unit sets upon.
Gas Heater Dangers
While natural gas is the most efficient type of furnace it is not without it's drawbacks. Natural Gas has certain dangers that you must be aware of to keep you and your family safe. Take a look at the items listed below if you have or are considering a natural gas furnace.
Forced air furnaces:
A gas furnace produces certain byproducts, the character and composition of which depends on the efficiency of the furnace. A gas furnace with leaks or cracks can be dangerous as it can leak carbon monoxide into your home. This gas is virtually undetectable because it doesn’t smell and you can’t see it. A carbon monoxide leak can make you sick with flu-like symptoms (such as headache, nausea, vomiting, dizziness, and fatigue) or, in severe cases, lead to death.
It’s important to have your gas furnace inspected once a year for any leaks through which gas could escape, as well as to make sure that the flame contains the right amounts of both gas and air. There is a safety switch and a limit switch that ensure the fan will run when the furnace is hot and that the entire unit will switch off if the flame exceeds its bounds. These features should be looked at as well during a safety check.
A vent less furnace has a switch to detect dangerous levels of carbon monoxide in the air, and this feature should be checked regularly as it is possible for it to stop working.
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| FURNACE, AIR HANDLER NOISE
There are some simple rules how to use this page:
Here are 28 different types of noises on this page. If, for example, you are looking for a Clicking noise find it right below, click on it and it will appear at the top of this page!
However, if you are looking for a Grinding noise scroll a couple of modules down and do what you just read above! Also, you can find the same kinds of "noises" in one of the next modules below.
I intentionally painted all names of the noises in the different colors, so it would be easier for you to find!
After you read on this page and watched video clips on the You Tube player below as a next step, you may call to an HVAC Company to fix the problem. If they cannot fix it, they will suggest you changing of your furnace out. If so, you have two options: they will do the job or you can do it as a DIY project. In both cases, I would advise you to visit the Furnace Book page on my website, because if the both ceases well educated customer is much better than uneducated one!
List of Noises:
Grinding noise
Buzzing noise
Clicking noise
Humming noise
Rattling noise
Rumbling noise 1
Rumbling noise 2
Squealing noise
Swoosh noise
Whining noise1
So here we go:
Furnace squeals
Squealing sounds from a forced-air furnace generally occur when the belt that connects the motor to the fan slips. If the blower is making a grinding noise, shut off the unit and call a furnace repair technician, the motor's bearings are probably shot.
In most cases, the belt is improperly aligned or worn and needs replacement. Follow the instructions in your owner's manual (if you don't have one, contact the manufacturer and ask for one).
This job involves removing the access panel, loosening a couple of bolts that hold the blower motor at the proper tension, and realigning or adjusting the belt. In many cases, it's a good idea to remove it and buy a replacement at the hardware store.
When reinstalling the belt, be careful not to over-tighten it this can wear out the motor bearings.
Furnace rattles
If the furnace makes rattling noises when it runs, be sure the cover panels are screwed on tight. If they aren't, tighten them.
Question
We live in a new house (built 2005) with up and downstairs furnaces. In the
last month, after the heater shuts off, we can hear a fairly loud buzzing
through our wall in our bedroom. I noticed the same noise in the living room
wall (same side of the house). I turned the thermostat to "off" and the buzzing
sound went away. Any clues?
Answer
A buzzing noise from a furnace is fairly common and is usually taken care of by tightening the mounting of the transformer. The unusual thing that you describe is that setting the thermostat to the OFF position stops the noise. Since nothing typically happens on any furnace until the thermostat calls for heat, it is unusual that setting the thermostat to OFF would do anything at all.
When you hear the humming noise, remove the cover to the burner compartment of your furnace. Try listening to hear which control or component is making the noise. If you find something that is humming you can usually get rid of the noise by tightening the mounting screws. In some extreme cases I have had to put a small piece of cardboard or plastic under the item and remount it.
If you don't hear anything in the burner compartment, you will need to remove the panel to the blower compartment. When you do this a door switch will open and cut off power to the furnace and stop the noise. Press the switch back down and listen for the noise. If you are able to figure out where it is coming from try tightening the mounting.
Needless to say, before you remove a control and try to remount it, be sure to turn off the power to the furnace.
Question
I recently had a Goodman high efficiency furnace (Model #GMV90703BXA) installed to replace my old furnace in a 25 year old 1900 sqft. Split level house. It is installed in the laundry room on the lower floor of the house. When it is on there is a loud whining noise on the upper floor above where the furnace is. When standing beside the furnace it sounds normal. I had the installer back in to check it and after doing nothing but look at the furnace for a few minutes, told me that it sounded normal. He didn't even go upstairs where the noise is. This is keeping my family awake at night so any suggestions would be really appreciated. Thanks.
Answer
Not good. I would turn off the furnace & turn on the blower only. This is high speed. Still hear the noise? Yes. Take off the lower panel on the furnace, trip the power switch to run the blower & see if the noise stops. If so, it may be air noise from a leak around the furnace base. When the panel is reinstalled & the blower running, go upstairs & listen to see if the noise gradually subsides as the blower slows down when the blower is turned off. If so, it is an air leak somewhere. If that doesn’t locate the noise I would turn the blower off, turn on the heat & check the combustion air blower motor inside the top panel for noise. If still have the noise it may be in the plenum on top of the furnace which would have been modified for the new furnace. Is it sealed well? Another check would be the return air grille for air noise, or even something in the return air plenum. I think you have an air leak that is projecting the noise up & thru the furnace. Look around carefully for leaks. Nothing inside the furnace should be able to create such a noise. Good luck.
Question
My furnace is approximately 3-5 yrs old (from what the seller told me) and it started making a clicking noise when it was ready to shut down after running a cycle. It runs the full cycle, the blower shuts off then the clicking starts. With the clicking you can also hear it make the swoosh noise it makes when the burner initially ignites, only it comes in several intervals with the clicking. you can kind of see little bursts of flames when it does this several times in a row then it shuts down completely.
Answer
Sounds like you have a clicking gas valve that is leaking gas. Causes could be tricky to find. First, I would check the low voltage wiring for loose terminals. Start at the gas valve & work backwards thru the air pressure switch & on to the circuit board. Next I would remove the hose from the combustion air motor to the air pressure switch, blow thru it to clean it. Then check the switch for obstructions. Next, start the combustion air motor & check for air blowing out the opening for the hose. Now, reassemble & retest the furnace. Next, if not OK, check the wiring at the thermostat for loose wiring terminals.
Question
Hello Dale. I have a Rheum electric heating and cooling system. A couple days ago, it started making a low rumbling noise. I have very little knowledge of these things, so I started looking for the obvious. First, I checked the outside unit. It sounded normal. The furnace is where the noise seems to be loudest (although it can be heard faintly through the vents, especially the intake, one floor directly above the unit). I started by taking off the panel that covers the compartment which houses the blower. As soon as I did, the rumbling stopped. As soon as I replaced the cover, the noise began again. I experience this whether the thermostat is set on heat, AC, or fan. I haven't really had time to sit around and wait but it seems that the system wants to run longer than usual before shutting off. Any Ideas? Thank you in advance for any help you might be able to offer.
Answer
In response to your question, you may want to check and see if your motor has oil ports if so you may want to try putting a few drops of oil in them if not you might call a service company and have them check the Amp draw of the blower hope this helps you some have a great summer!
Question
Rumble from furnace!
I have a oil burning-hot water heating furnace that is original to my house(1985). Lately I have noticed that when the furnace shuts down after a heating cycle, there is a loud rumble that shakes the house. It never has done this in the few months that we lived here until a couple of weeks ago. Is this a sign that this thing is on its way out or ready to explode and kill us all? Really would like some input.
Answer
Get it checked by a Pro ASAP. Rumbling is usually caused by unburnt oil in the combustion chamber burning badly after the burner shuts off. Usually is caused by a dirty or dripping nozzle. It is very unsafe as well and can produce CO if not setup properly.
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List of Noises:
Clicking noise
Humming noise
Moaning noise
Rattling noise
Squealing noise
Train like noise
Random noise
Weird noise
Hammering noise
Question
I have a high efficiency Rued furnace that was installed in our home when it was built in 1993. In the last couple of the furnace has started to make a noise about 30 seconds before the blower kicks on. It is loudest in the morning when everything is cool after the heat has been reduced for the night. The furnace will start the fire in the combustion chamber and build the heat. About 30 seconds before the blower kicks on there is a rattle noise that can be heard through out the whole house and in the quiet mornings is quite loud. The rattle sounds like a vibrating water pipe if that helps. I've tried standing by the furnace and can't isolate where the noise is coming from. I would appreciate any ideas that you might have.
Answer
It sounds like a problem with the heat exchanger. It may have developed a crack and as the exchanger heats up, it will make sometimes a sound as you describe, or a loud bang when it expands. It needs to be checked ASAP as carbon monoxide could enter the ductwork if there is a crack. I also always recommend a good detector for carbon monoxide with any fuel burning device.
Question
Hi, I have a Hail Gas Furnace with a self igniter. Everything runs good except for a clicking noise that won't stop, it sounds like it's the igniter. When I turn of the gas and unplug the spark plug wire, there is a low humming noise that sounds like it's coming from the control module. I'm thinking there is a problem with the Honeywell control module. What do you think? Thanks.
Answer
Check the flame sensor and make sure its clean. if it still clicks i would think about changing the sensor.
Question
It has been several months now that my gas heating furnace kept making some noise. This noise is random. Whenever this noise occurs, there is no air blowing from the vent on the floor. This noise last the same duration as when it was working fine. My guess is that whenever this noise occurs, the fan in the furnace does not turn.
The furnace brand is Carrier.
Any help will be much appreciated.
Answer
I would first check the blower to see if it was tight and that you couldn't move it to the point where the blower might contact the sides of the housing. At the same time, checks to see that the motor mounting bolts are tight.
Question
Heating season just starting here in Minnesota and when the blower runs there is a new noise the furnace hasn't had in prior years - a mild moaning or groaning noise of a type which makes me think the motor is in the early stages of an eventual failure. I get nervous at the thought of having an emergency service call three months from now when it is 10 below zero. So, here are my questions:
First, is there anything I can investigate further or try myself in hopes of reducing the likelihood of a potential repair call this winter?
Second, if the motor does go or should be replaced now, is this something I could do myself?
Third, this furnace is more than 25 years old. It has proved reliable through that time with minimal service costs, mostly cleaning. Given the age and probable low efficiency of the furnace, is it more cost-effective to replace it? Money is tight right now so that is a factor in balancing the limp along vs. replaces equation. On the other hand, it is an old house and a cold climate and heating per month is high so there clearly could be a substantial payback to greater efficiency.
Answer
Sounds like worn motor bearings. Grasping the motor shaft and moving it up and down (perpendicular to the motor) you should not feel any play. Side to side movement is normal. If all it takes is a new motor to keep it rolling you shouldn't be in for more than $100-$150 if you do it yourself.
Question
My Hydro flame furnace works and heats just great but it has started squealing and sounds like the house is coming down! Is there anything that needs grease? Any ideas? Thank you.
The bushings in the motor are "dry" To go dry they have to be worn out. The bushing material has lube in it. For the bushings to squeal it means the portion of the bushing with the lube in it is worn through. If it is still working you could access the motor and lube the bushings. This is only a temporary fix. I think that once you have excavated and disassembled all the way to the motor you will just replace it. No matter what furnace you have it's a pain. Good Luck
My furnace blower recently started making a loud, low, steady train like noise every time it comes on. It is not a higher pitched squeak, but more like an engine. It is moving air and the cage is spinning. My furnace is supposed to be a perm lubricated motor.
Answer
I am guessing that your blower is a direct drive blower, meaning that the blower wheel is attached directly to the motor shaft. The way you described the noise leads me to believe that the motor bearings are bad. This is the most common reason for noise coming from the blower compartment. About the only remedy to this is to replace the motor. You say that you motor is permanently oiled, that is just a way of saying that it can not be oiled and not being oiled is what causes them to wear out. I don't know what kind of furnace you have but in my area is it is a standard furnace and a regular sized motor and a normal installation the price range for the complete job would be somewhere around $230.00. If you had access to buying the motor and a capacitor you would get by for around about $125 to $150. Post if you need more Information. Hope this helps.
One last thought, with the furnace unplugged feel all around in the blower wheel to make sure that something has not been sucked into the blower wheel and it might be rubbing on something. Use a flashlight and look very good.
Question
I was out of town for a couple days; I came home to hear weird noise from furnace. It appears my fan has loosened and is brushing against the housing. Is there an easy solution?
Answer
Setscrew probably came loose. Turn power off to furnace.
Reach hand in blower wheel on left side. Feel around hub. You will find a setscrew. Probably loose. Move blower wheel back to center on housing. Align setscrew with flat spot on shaft. Tighten screw.
You should check to make sure that motor shaft is not rounded.
Question and Answer
Model # NUG9100FHB1 it is a high efficiency furnace.
There are four burners (in shot type), I have cleaned all the burners at the front I can get a dime just to start in the opening. My pilot comes on, it is not plugged, when the pilot comes on and the burners ignite the furnace hammers hard...the furnace is located in the basement and I can hear it loudly and feel it bang all the way upstairs.
I have tried adjusting the pilot for less and more pressure and that does not help. The problem is intermittent it comes and goes, more so there then not but sometimes it doesn’t bang...does anyone know what might be the problem and how to fix it? My fresh air or intake is not obstructed.
Call us crazy, but had my boss come out and we did more troubleshooting. Disconnected the igniter from the burner assy. using a torch we kept that lit at the burners with the pilot and igniter assy. outside the furnace, called for heat and the burners lit and the pilot didn't come on until about 3 seconds after the burners lit so thinking it might be a faulty circuit board?. My understanding from what people have told me is either that it is probably not a bad gas valve, they work or they do not there is no grey area is that correct.
I have a nice blue flame on all four cells there is no red, when furnace is on so we are pretty sure heat exchanger is not cracked.
I put the pilot assy back together last night after my boss helped with the trouble shooting as stated in the previous post then took the lower cover off to check out the bottom half which just has the blower and circuit board.
The key here I think, is as I stated in an earlier reply is that the house sat vacant for at least a year if not more. I wiggled all the stake on connections on the circuit board and the plastic connection going to the igniter and pilot assy. The furnace has been firing up fine every time no more hammering during ignition!
So not knowing anything about this stuff without proper test equipment my guess is that I had corrosion build up on connectors from sitting so long or there is a short somewhere and the jiggling of the wires helped.
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List of Noises:
Furnace noise
Grinding noise
Humming noise
Rattling noise
Vibration noise1
Whining noise2
Howling noise
Sputtering noise
Humming/roaring noise
High pitched whine 3
Vibrating nose 2
Question
Reducing furnace noise?
I'm trying to cut down on the sound coming off our home furnace. I already have the furnace room walls insulated with rock wool, which I find insufficient. Short of adding more wall sound insulation, is there anything that I can add directly on to the furnace unit itself to block the noise?
Answer
It depends on what about the furnace unit is making the noise.
Typically it is the fan motor, or associated moving parts.
Sometimes it is the housing vibrating from the spinning of the blower fan. It may be the plenum or metal (or other) box that the air blows through to get to the ductwork.
Let’s look at all reasons it can make noise and eliminate things
First, the fan. If the furnace/ac kicks on and there is a rattling or grinding or whining or other noise that accelerates as the fan picks up speed, the bearings in the fan blades or motor are going bad. This is not good / expensive to fix maybe.
IF the noise is worse when the fan is at full speed and stays constant while the unit is blowing air it could be that the belt is loose or if no belt the linkage from motor to blower fan is loose or worn out. This may be fixable with a little tinkering but not for someone not mechanically inclined. The mounting for the motor or fan blower may be loose, try to tighten the screws or bolts that hold them down.
If the noise starts slowly after the fan is at full speed it could be that there is resistance in the plenum or ductwork/air ducts/vents. This usually isn't that noisy, but it can be bad.
You should go throughout the house in each room and make sure that the ducts are clear and vents are all open to the full. Usually there are fins that direct the flow to a certain direction these should be open wide, also behind them may be a flow restrictor fins. These are used typically with a lever that opens or close the flow off completely to 'zone control' the room. These should be open wide as can be too for the testing. Should be so the air ducts and vents in each room are open wide and blowing air full when the unit is operating. Be thorough as you search for vents in all rooms, you may miss a vent or two in odd rooms, behind furniture or in larger rooms. If any air vents are open wide and don't blow air with good force (should be similar from vent to vent and from room to room, decreasing slightly the farther from the furnace unit you get) then the ducts (tubes) are blocked somehow. If they are in the attic, they may have been crushed by the cable guy or the Christmas ornaments box you shoved up there. Or maybe you have squirrels building nests within them or something (similar in the basement depending where the ductwork runs.)
If they are smashed, reshape as best you can and see if that gets the air going again. (Careful not to tear them open or cause leaks in the duct itself) If too much air is restricted from coming through the ducts it can make the unit noisier. If the ducts leak into the attic or basement you lose heat/cool into that space instead of the room and could cause water damage from condensation. Seal leaks with duct tape or replace the duct.
Same goes for the return air intake(s) usually there is one at the furnace unit on the door to the unit or an adjacent wall. The filter usually goes there. The filter should be clean and fit properly for the opening so all air goes through it not around the edges. Other return air ducts can be placed throughout the house in larger homes so check that the same as the air ducts and clear any blockages. Sometime when the unit is installed, the unit is too powerful for the size of ductwork existing and this can backpressure the unit causing excessive noise and resultant loss of efficiency of the entire unit. It is working too hard to force air through it. This is hard to calculate, a bigger plenum and more ductwork is required.
Other major noise may be the plenum, duct work, vents or surrounding wallboard or the floor where the unit sits may be loose and making vibration noise that can be dampened by securing it properly/better... if it is rattling or humming it may be the plenum or duct work. Tap on the plenum and ducts to see how loose they are and if so, try to screw rivet or tape the parts that are noisy so they can't flex so much. This may dampen the sound a bit.
Make sure that the floor under the unit is solid and doesn't have any weakness at all.
Sometimes there is water damage from condensation or poorly braced for the weight of the unit or other reasons that weakens the joists or flooring and that can really make it noisy but not be obvious. Unfortunately, this may be an expensive or extensive job to fix but maybe worth the trouble if the floor is damaged enough to break under the unit.
This should eliminate most of the noise of the unit that can be fixed. Sometimes you just have a noisy unit. In that case, there are other things to do to help quiet the environment of your living space.
If the furnace is in a wall that adjoins the bedroom or living areas, you might try to place larger pieces of furniture in front of the area where it is. Like putting your big dresser on that wall right where the furnace is located. Maybe hang a tapestry on that wall as well will help quiet it some.
Move the bed or your sitting chair to the other side of the room from the furnace.
Another more extensive fix can be to double up the drywall board around where the furnace is to quiet it down. This seems radical, but it will reduce a noisy unit significantly if done properly. (Last resort stuff)
In short, Eliminate any vibration noise, air flow restriction noise, or structural weakening, use sound barriers in the rooms or consider replacing the furnace altogether.
Question
Just trying to find out why my furnace makes a very loud howling noise when it kicks on. I thought it might be vibration between the fuel rails when they heat up so I took them out and cleaned them, didn't work. It seems to start howling after the fan kicks on, but the noise isn't coming from the fan. The furnace was checked by a local company with a good rep two years ago but with the times now I'm trying to save some money. It is an Air-Ease gas furnace about 19 years old, but hopefully I won't need a new one. Also sometimes it makes a loud bang when the gas starts going to the rails. Any advice would be great.
Answer
I would energize the fan only first to determine if the noise possibly comes from the duct work. By the way your description, I have a feeling it is a heat exchanger issue. You can take one of those long lighters, and insert it in each of the burner ports. If the flame "wanders" (while the fan is energized) then it is likely you have a crack in the heat exchanger.
Question
I just had a new Miller oil furnace installed in my mobile home one month ago.
When it starts, it starts with a Womp! Then as it burns, is sounds like it sputtering like--putt, putt, putt, putt,-until the heater shuts off.
I thought I read in the manual that this is normal but should even out as it burns but it does not even out. Something does not sound right to me.
Is there any danger in this? Could this damage the inside?
The furnace does not put out any soot or any smoke or anything like that and it gives good heat.
Being in a mobile home it sounds like the furnace is going to go through the wall when it starts. Any suggestions?
Answer
This can be VERY DANGEROUS!!! The burner is not setup properly. You are getting delayed ignition and it sounds like the fuel too air mixture is wrong. Get it checked ASAP and yes the pulsating can and may have damaged the combustion chamber.
Question
Vibrating Inducer Motor
Hello, my Carrier furnace has started making a very loud hum/roar. It is extremely loud when in second stage. I have narrowed it down to the inducer motor. When I put pressure on the housing, the vibrating noise/roar goes away.
Do I need a new one or can this be adjusted?
Answer
Those Carrier inducers are notorious for that problem. You need a new motor and wheel and the wheel is very easy to bend/warp when installing so be gentle with it.
Question
We recently moved into our new house and I've started to notice a high pitched whine coming from the furnace. The house has 2 zones, and I only notice the whine when zone 2 (the 2nd floor) of the house is heated. There is no whine when zone 1 is heated. The furnace is a Lennox G61MPV gas furnace with a variable speed blower.
I had the HVAC installer come out this morning to take a look. He verified that the whine only happens when heating zone 2 and when the blower kicks up to its highest speed. He said that the reason I don't hear it for zone 1 was that the blower doesn't have to run as fast since the air is only going to the first floor. He examined the blower, tested the amps output, and observed the fan wheel and everything seems to be operating correctly so he can't replace the blower since there is nothing technically wrong with it. I'm a bit frustrated since I believe it shouldn't make that noise at high speed. They are going to follow up but he said that it could be an airflow issue for zone 2 and that they may need to replace some vents with grills to increase air flow in zone 2.
Answer
Most likely it is going to be a velocity issue in a duct. But I have run into this twice now on my installs, and helped a couple of other friends who were about to kill themselves or the customer over this issue. The best way I can describe it is that it sounds like when you run your finger around the top of a whine glass, or when you strike and hold a tuning fork. Yes, the way I fixed one is take out blower and use a tape to keep the metal housing of the blower from actually coming in contact with its track on the air handler. But that was just because I could not fix duct issue that was causing the ecm to run at that high rpm. The others have been fixed by fixing static pressure problems that allowed the motor to ramp down and run at different rpm. P>S> most times this ringing sound or noise will be just whistling thru ducts. But the sound I am talking about is generated from the unit itself.
Also, you need to add more ductwork to the second floor or add a by-pass damper. Or you possibly could "dump" some air somewhere. I put in a "wild" zone when I did mine. The ECM motor will ramp up (more airflow) if there is restriction to the airflow. This, of course, results in air noise and/or vibrations somewhere.
Question
Last night around midnight my upstairs air-handler started to sound like a diesel truck in idle.
I climbed up into the attic to see the unit swaying in its straps and vibrating like crazy. Being so late I was not going to deal with it then.
Fearing I had a failing blower motor I prepared for the big bill from my HVAC company.
Today despite being 97 out I ventured up into the attic to take a look. Pulled off the access panel and as the blower came to a stop I heard a distinct whooshing sound. Once it stopped I saw my problem. The wiring schematic had come loose from inside the chamber and got sucked into the blower. I pulled it out, dusted off the the fins and the motor and started the sucker up. Quiet as a baby and no more shake. Amazing how a piece of paper 5x8 inches can completely throw the balance off. You would have thought there was a wet towel in there.
I am sure the HVAC people would have charged me $100 to come out and clean that out.
I think that was worth the sweat.
Fans
Duct Fans
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58. FURNACE CHANGE OUT – the chapter is dedicated to the other part of the trade and describes everything what an
  installer suppose to know to perform furnaces replacement.
The chapter has 24 pictures; 4 pages.  10.62 (Instant Access)
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Below you can watch fifteen very useful video clips from YouTube dedicated to the furnace repair issues. If you are not completely satisfied with information on this page you can find much more useful information on the other websites above and below of the YouTube unit.
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