As far as safety is concerned, the exhaust pipe is one of the most important parts of a furnace. Why is that?
The exhaust pipe is responsible for removing poisonous flue gases from your furnace. If the exhaust pipe is blocked or broken, harmful gases can get into your home’s air.
In this article, I’ll explain what a furnace’s exhaust pipe is for. I’ll also discuss what factors you need to consider when venting a furnace, and how to identify a furnace by its exhaust pipe.
How does the furnace exhaust pipe work?
When your furnace burns gas, it creates heat, water vapor, and carbon dioxide. As part of the combustion process, by-products are produced: Nitrogen oxides, sulfur oxides, and most notably—carbon monoxide (CO).
The exhaust pipe’s job is to remove these harmful gases from your home and vent them outside.
How does the exhaust pipe remove flue gases from your furnace?
The exhaust pipe is attached to the inducer fan. The inducer fan creates a draft through your furnace’s combustion chamber and heat exchanger. As the gas undergoes combustion, the flue gases flow through the heat exchanger and exhaust pipe. The flue gases exit the exhaust pipe and get dumped outside your home.
Where is the furnace exhaust vent located?
Your furnace’s exhaust vent is located on the outside of your home.
If you have a standard-efficiency furnace, then your exhaust vent should be located on the roof.
If you have a high-efficiency furnace, then your exhaust vent should be located on the roof or on the side of your home.
Why does the location of the exhaust vent differ between standard and high-efficiency furnaces?
It’s due to the contents of the furnace exhaust.
In standard-efficiency furnaces, the exhaust contains hot gases. Because of the high temperature of the exhaust, the gases naturally draft up. This is why the exhaust vent for a standard-efficiency furnace is located on the roof of the home.
In high-efficiency furnaces, the exhaust contains mostly water and carbon dioxide. The exhaust from a high-efficiency furnace is not hot enough to rise up on its own. Instead, an inducer fan is used to push the exhaust out of the house through a venting pipe.
High efficiency (condensing) furnace venting
Venting for high-efficiency condensing furnaces is a complicated topic since there are many factors at play. Especially if you’re retrofitting a high-efficiency furnace into an older home.
There are two types of high-efficiency furnace venting setups: single-pipe and two-pipe. Both have their pros and cons. The one that is best for your home depends on a myriad of factors:
- Availability of existing venting systems to use as a chase
- Local government codes and homeowner association rules
- Location of the furnace in your home
- Venting setup of other appliances
- Airtightness of home
For more information about venting a high-efficiency furnace, check out my article below:
What if you have PVC furnace intake and exhaust pipes?
If you have PVC intake and exhaust pipes for your furnace, then you have a high-efficiency furnace.
Why are PVC pipes needed for high-efficiency furnaces?
PVC pipes are needed for high-efficiency furnaces due to the contents of the furnace’s exhaust.
Exhaust from high-efficiency furnaces contains acidic water. The acidic water will corrode metal exhaust pipes quickly. PVC does not corrode, so PVC pipes are used instead.
Furnace PVC exhaust pipe condensation
If you have a high-efficiency furnace, then its PVC exhaust pipes will need to be sloped towards the furnace.
Specifically, most installations require a minimum of ¼” of slope per foot of pipe. This allows the furnace condensate to flow back towards the furnace’s drain pipe. This keeps the furnace’s condensate contained inside your furnace’s drainage system.
Why can’t the furnace condensate be drained outside?
There are two reasons why furnace condensate shouldn’t be drained outside:
- If the condensate flows outside, then it may freeze if outdoor temperatures get too low. Frozen condensate can break your PVC exhaust piping.
- Some areas don’t allow you to drain furnace condensate onto the ground because its acidity may pollute the groundwater.
What if you have a metal furnace exhaust pipe?
If your furnace’s exhaust pipe is made out of metal, then you have a standard-efficiency furnace.
Why are metal exhaust pipes needed for standard efficiency furnaces?
Metal pipes are needed for standard efficiency furnaces due to the high temperature of the exhaust.
How hot is gas furnace exhaust?
Exhaust temperatures from standard efficiency furnaces are usually in the 300-400° F range. The exhaust gases from a standard-efficiency furnace are hot enough to melt a PVC pipe. That’s why standard-efficiency furnaces use metal exhaust pipes.
Do you need a gas furnace exhaust fan?
Almost all furnace exhaust systems use an exhaust fan to push the flue gases outside. An exhaust fan for furnace flue gases is called an inducer. The inducer is built into the furnace and turns on whenever the furnace heats your home.
Some older furnaces use a natural draft system to expel flue gases from the home. In a natural draft furnace, there is no inducer fan. Instead, the hot flue gases naturally flow upwards out of the home through a flue pipe or chimney.
If you have an older natural draft furnace, you probably don’t need an exhaust fan. Natural draft furnaces are installed in such a way that does not require an exhaust fan for the flue gases.
If you have a newer furnace then your furnace will have an inducer fan built into it. So there’s no need to install a separate exhaust fan.
Are you following my furnace exhaust blog series?
Are you having trouble with your furnace’s exhaust system? I’ve written a bunch of blogs answering questions that people have about fixing their furnace’s exhaust systen. You can check them out by clicking the links below.
I have a standard efficiency furnace with metal exhaust piping and have a condensation problem with water dripping into my fireplace in the winter when it is not raining
Hi Pat,
Standard efficiency furnace condensate can be caused by an improperly sized exhaust pipe or combustion issues. Either way, it’s a serious issue and you should turn off your furnace and get it checked out by an HVAC professional ASAP.
-Trey
Hi. We have a gas and electric furnace. Separate air conditioner unit. The furnace appears to be working fine. But we have an exhaust smell in the house. Is it a clogged exhaust pipe? Or a vent issue? Help?
Hi. We have a gas and electric furnace. Separate air conditioner unit. The furnace appears to be working fine. But we have an exhaust smell in the house. Is it a clogged exhaust pipe? Or a vent issue? Help?
I have a standard efficiency gas furnace with the exhaust through the roof. My question is should the metal flue plate be in or taken out before running my furnace ?
Is it allowable to have the high efficiency exhaust pipe have a 90 degree elbow near the termination where the pipe will drop 18 inches followed by another 90 degree to go through the outside wall?
Hey trey this is probably a stupid question not sure if yur hvac but sounds like yu kno furnaces i kno nothing really about em just wut the supply n cold air return dose…
I kno the heat exchanger in the furnace heats up the furnace not to sure about the secondary heat exchanger n the blower fan blows it threw the supply im probably wrong lol..But anyways on the furnace the intake pipe that leads outside.. is it supposed to blow white thick heavy smoke alot of smoke is coming from that pipe outside…obviously when the furnace is running of course…i thought it was supposed to intake all the serious gases from the furnace an evaporator it as it blows air out the pipe n not blow white smoke i don’t know im probably wrong again lol but thank yu if yu can get back to me my names Matt
Hey trey not sure if my comment went threw can yu email me plz
I have a high effiency furnace using black pvc pipe and had my furnace tech installing a digital thermostat told me it should be white pvc because the black one will crack over time ,is this true
Hi Dwayne,
The color of the pipe does not matter.
However, there’s a good chance that the “black PVC pipe” installed on your furnace is actually ABS pipe. Certain types of ABS pipe can be used for furnace venting in some areas. It depends on your local codes.
Some older types of ABS pipes were known for cracking. However, the newer types of ABS don’t have the same issues, as long as they are made for venting purposes.
Hope this helps,
-Trey
I have a standard hvac system with a metal pipe coming from it going to the water heater vent. The natal gets very hot and. When is it required to have double indicated pipes so no one gets burned by this pioe?
I have a high efficiency propane furnace (not natural gas) and I have two pipes coming out of the roof. The fresh air intake pipe is about 1 1/2 feet shorter than the exhaust pipe and has an elbow on top facing away from the exhaust pipe. For the second time, I have smelled furnace exhaust in my house. I have had to open the doors to clear the air. I have kept the snow away from the pipes. (our snow is measured in feet). Is it possible that, depending on the barometric pressure, the heavier exhaust gas is floating down and getting sucked into the fresh air intake pipe? My furnace is about three years old and this has only occurred twice.
Hi Sharon,
I’m not sure if your “fresh air intake pipe” is for fresh outside air for your home or furnace combustion air. Either way, you should not be smelling furnace exhaust in your home. I recommend getting an HVAC professional to take a look at your system.
Hope this helps,
-Trey
I recently cut a hole into a wall to frame a door and discovered a pvc pipe. It’s not connected to any water so I’m assuming it’s running from the furnace (not gas) in the crawl space, up two floors to the roof. I rerouted the pipe so it would run along the side of the new door but now I’m paranoid about whether anything toxic is coming out into the air. What is the best way to verify everything is sealed properly and nothing is leaking?
I had a new high efficiency furnace with a concentric pic exhaust pipe/air intake set up installed last winter. We had no problems last winter. This year we are hearing loud knocking noises where within 1 foot of where the pipe leaves the side of the house, We’ve been told by several heating contractors that they have never heard of such a thing, but could be the pic pipe expanding and contracting. So far no one has come up with a solution to get rid of the knocking. Any thoughts.
Hi Linda,
My guess is that the PVC pipe is expanding into the side of your house when it heats up.
If there isn’t enough clearance between the pipe and the hole that it goes through, the pipe will sometimes make popping noises as it expands and rubs up against the side of the hole.
My recommendation would be to ensure that the pipe moves freely through the hole and has a gap around it to account for thermal expansion.
Hope this helps,
-Trey
Hi. I have what I think is a standard efficiency standard draft furnace. Metal pipe exhausts to side wall in basement into outdoor cinder block chimney. When burning wood upstairs (different chimney) the furnace doesn’t come on, the exhaust pipe gets cold and doesn’t exhaust out, so the furnace shuts off (good safety measure) Can I insulate the furnace exhaust pipe from furnace to wall and if so would that solve this problem? Thanks, Wendy in Vermont
Hi there – I just purchased a home and it has a propane gas furnace and two pvc pipes about 2 1/2″ diameter coming out the roof. One pipe has a 180 degree elbow and the opening of that pipe faces back towards the roof. The other pipe is straight up and open without any fitting on the end, much like a vent for plumbing would be. I’m wondering whether its ok for the pipe that is open and facing straight up to be like that, such that rain water and snow will come into the pipe and into the furnace? I was thinking about putting some sort of cap on it that would allow it to vent, but not allow water to get in. Should I do that, or just let the rain come in. I have looked at the furnace and I can’t determine if it has a water outflow to allow the rain to get out somehow. Thanks in advance!
We live in Minnesota and our exhaust pipe gets an icicle on it. will this clog up the pipe eventually? Will appreciate your answerMy husband is paranoid about this and thinks we have to go out and knock this ice off every day.
I have a standard unit and the exhaust pipe gets extremely hot. Also I see where the metal pipe vents at the roof vent there is a lot of hot air rolling back into the attic. The end of the pipe is about 6″ into the roof vent but the metal pipe does not touch and seal to the roof vent pipe. There’s about an 1 1/2″ gap all around. It feels like a lot of hot air rolling back into the attic. I don’t know how strong the air flow in a vent is supposed to be but mine is pretty strong. Any thoughts?
I put a new deck on my house and added 16 ft. To my exhaust and intake pvc. I am now having freezing issues. Any ideas on a fix?
I have a standard efficiency ceiling mount furnace with metal pipe. I have tried difference type of caps but when it rains hard and is windy it leaks into the house.
Can I add a curved piece on the pipe coming out of the roof?
Thanks!
Have a high efficiency Amana furnace with PVC exhaust and intake through the side of the house.
How far apart should the exhaust and intake be outside the house? My concern is that the intake is pulling in damp air that is exhausted from the furnace, causing excessive moisture building up in the inlet line.
Appreciate any info.
Thanks
Are there any restrictions on the length of both the intake and exhaust pipes coming out the side of my house.Right now the extremely close to the ground and I have to shovel constantly to prevent it from shutting down.i want to extend exhaust up 30 inch and intake 20 inchs.can I do it?
Installed a new bryant furnace. The inductor motor wines when it starts up. Have replaced with a new assembly and still had the wineing noise. Techs don’t know what to do.
I installed a new 80 efficiency furnace that replaced a 28 year old system. I do not believe the old system had a draft inducer and the system was exhausted using a sidewall mounted power venter. New unit with a built in draft inducer was attached to flue with sidewall power venter and the new furnace does not ignite 20% of time with an error code stating pressure code stuck closed when should be open. Is there a problem with having both a unit draft inducer and a power venter?
Is it ok to have your natural gas grill within 10 feet of your high efficiency gas furnace termination pipe?
Hello
I have a 3 yrs old house with high efficiency furnace (with a concentric pic exhaust pipe/air intake set up). Staring last year,
drifting snow and/or ice formation block the exhaust or intake pipe or both and cause the furnace to go into safety lockout mode and shut down automatically. Usually I clean (couple of times, in the middle of the night) the exhaust/intake pipe/vents outside & the furnace starts to work again. My questions why this happens? is this normal problem? is the issue with the way the pipes installed or the fan inside the furnace or what?
Thank you
Hi Ephrem,
Your issue seems to be the location of the intake/exhaust vent. I recommend getting a local HVAC professional to check out your system to see what can be done to fix it.
Hope this helps,
-Trey
Elbow up the pipes past the area of 100 year snowfall heights then screen and rain cap on the exhaust and fresh air intake. Run the exhaust higher than the fresh air to avoid coming ling the two. The hot air rises always.
Bryant Model 926TB
We had this unit put in about 5 months ago, it seems there is an excess of fumes through out the house, what can I do?
what is the purpose of the round topper on the furnace vent on the roof and does it need to have one?
Hi Al,
Great question. The roof vent cap is needed to protect the interior of the exhaust pipe and prevent debris from getting inside of the furnace’s exhaust venting system.
Hope this helps,
-Trey
I have a HE Trane gas furnace with two long pipes (about 40 feet) vented through the side of the house. My furnace is shutting down after a few minutes and I have isolated the trigger to the flame rollout sensor. I’ve read that an exhaust obstruction could lead to improper combustion and cause this sensor to trip. The PVC exhaust piping is all tightly glued together and clamped down. Do I need to start cutting to gain access to clean it? I tried suction with a large shop vacuum at the exhaust end but I don’t think it provided enough vacuum to overcome the long run of slightly upward tilting pipe.
Hi Roger,
That’s a tricky problem. I recommend calling a professional to check it out so you don’t go down the wrong path.
A new furnace was installed, the new vent pipe was installed on top of the old one , so it’s twice as tall. On strong windy days , I hear a load whistling sound. why?
Hi Bill,
That could be the top of the vent pipe whistling from the wind. I would get it checked out to make sure there aren’t any other problems. If no other problems, you can also install a vent hood over the top if it keeps whistling as long as it doesn’t restrict the flow of exhaust from the vent pipe.
-Trey
A high wind exhaust cap is needed.
I’ve had occasional high press switch error codes on my Rheem 95 pct. RGFD that trip the burner from lighting. I can’t find any obstruction and I changed the high press switch. The oval metal capacitor on the inducer motor is very rusty. I bought a new one, but I can see no +/- markings on either the old one or the new one. Is the capacitor non electrolytic/non polarized, or is the motor AC, so that it doesn’t matter which wire connects to which capacitor terminal?
Thanks.
Hi Mike,
I’m assuming that you have a run capacitor with two terminals. If that’s the case then you’re correct – it doesn’t matter which wire connects to which terminal.
-Trey
Hello Trey
I had a new HE furnace installed 5 years ago. My contractor re used the old exhaust pipe (at least the part that extends above the roof). Since I got the new system, my gas usage is higher by 20-30%. Could ventilation be my problem?
Paul
Hi Paul,
There are all sorts of factors that could be the problem, ventiliation is just one of them. Get a diagnosis from a different company to see whether the increased gas usage is normal or not.
Hi I have a high efficiency furnace. My neighbor recently installed a heat pump unit outside and the fan is blowing directly at my exhaust flue. Distanace from heat pump and flue terminal is 15inches. Will my fumes be vented adequately?
Our furnace is 4 yrs old and quit working yesterday. Had repair guy over and found out the inducer motor he took apart and found remaining pieces of a rubber/plastic gasket restricting the exhaust fan from working. Pulling a couple strips out with pliers and allowing fan to blow out remaining little pieces the fan/motor works again. Question.. where did the old gasket pieces come from?
What is the usual exhaust vent pressure on a 90+gas furnace?
Hi,
I have two PVC pipes, one labeled EF, which I noticed had a hole that was covered with mirrored tape. I noticed today that the hole was exposed. I have an image but not sure how to post that. Should the hole be covered or exposed? Concerned about gas fumes in my home and safety.
Hello. My neighbor is nuts & keeps spraying Glade in my furnace vent. One night I layed down & heard him spraying 7, yes seven, cans of Glade in my furnace vent. It gave me a headache & my heart was racing & my ears ring eventually made me sick to my stomach plus I use an albutural inhaler. He told the police….. I was crazy BUT what 60 year old man does this!? I bought this house 19 years ago, he greeted me with “ Fu@k you bit@h! “ I don’t know if I over bid him on this house or what. So my question is. Which vent blows IN to my house? Are there little louvers I can put in side the pipes so Glade can’t come in? Seriously. Robin 69 years old and I live alone. Please help me
I have a standard furnace with a metal vent pipe. I had a leak at the vent pipe and boot connection which I caulked. Later I found out the caulk is only good to 200°, will that be a problem for fire or will it just fail. The product is flammable before it cures it has mineral spirits in the product.
Hi Sam,
Furnace exhaust vents should be sealed with high-temperature silicone caulk
-Trey
I have a 80% efficiency furnace that was just installed by professionals. They came back and put skirts around the holes they made for the exhaust vent duct work except in one place. I was thinking about using expandable foam around that area to seal it up. The foam (MSDS sheet) says its good for up to 194* F as a service temperature
and the wall that this area pertains to (that is exposed) is about 3 feet away from the actual furnace flame. Is the only way to know for sure whether this would be an ok idea to fire up the furnace and measure the ductwork in that area with a digital thermometer ?
Hi Kevin,
You should check with the furnace installers if there was a reason why did not put skirts around that particular hole – there could be a reason they left it that way.
-Trey
Morning,
I recently had a Goodman 80% furnace installed and I noticed that a rubber boot came with the furnace for the exhaust vent connection at the furnace itself. This boot obviously gets hot when the furnace is running. Should there be a different type of connection there from the furnace to the vent pipe? Or does the rubber boot with hose clamps provided suffice? Thanks.
Hi James,
It depends on the type of exhaust venting that was used and the building codes in your local jurisdiction. If you are worried you can contact your local building inspector’s office since they will know what is allowed.
Hope this helps,
-Trey
Update: the boot was not included with the furnace. So my follow up question is, what is the best way to connect the exhaust vent pipe to the exhaust outlet on the furnace? Thanks again.
I have a standard furnace with a metal vent pipe.
Should there be screws holding the exhaust pipe to the outside pipe?
There are holes there but no screws and no clamp of any kind.
It’s separated and we’ve been dealing carbon monoxide poisoning. Very glad to be alive.
But…I wonder why they weren’t screws put in.
Should there have been?
can a high efficiency furnace have too much slope on the exhaust?
meaning slanted at say 45 degree angle
Can a high efficiency furnace have too much slope on the exhaust PVC?
meaning slanted at say 45 degree angle
Hi Max,
Generally you can’t have too much slope, only too little slope. However, you should consult with the local codes in your area to see if your specific venting setup follows the requirements.
-Trey
Hello, I have an old gravity furnace. Any idea how hot it gets? The exhaust duct.
Hi,
Just replaced an old furnace with Trance high efficiency, the exhaust pipe run through the outside but the air intake pipe is inside just 3 inches long on top of the furnace. Is this a safe installation?
Hi Wil,
The safety of that installation depends on a lot of factors. One place to start is to check the building codes in your area, that will govern what is considered a correct and safe installation.
-Trey
Hey,
I it seems I have a high efficiency furnace (PVC flue vented on the side of the house) and my furnace keeps tripping the high limit switch every 6 minutes on the dot. It stays off for 3 minutes with the blower still blowing air then turns back on and the cycle repeats forever. I was wondering is it possible that the switch is just faulty and opening too soon? It doesn’t seem to me I have a restriction on any of my vents the air seems to flow good on every vent. Is there anything else I can do to find the cause?
Hi Andrey,
High limit switch tripping is usually due to airflow issues. It is possible that the switch itself is bad, that does happen from time to time.
Here is my article on high limit switch tripping if you need more info: https://hvactrainingshop.com/furnace-high-limit-switch-tripping/
-Trey
Hi thanks for all the advice. We have closed loop furnace with the pvc pipe furnace exhaust going to the outside (high efficiency). We noticed that the pvc pipe has some orange build-up on the end of the pipe (there is no grate for bird cover etc.) It looks like rust but obviously pvc should not rust, any thoughts on what this is? thanks
I do have a high-efficiency furnace 2 PVC pipe system. I live in Wisconsin freezing temps for winter. I know that my exhaust pipe is NOT pitched 1/4″ per foot toward the furnace. If I have the exhaust pipe is turned up outside the house, and the intake down the exhaust does freeze. Could I drill say a 3/8″ hole in the elbow to help drain the water. And is this setup for directions of the pipes correct for the area?
Hi Wayne,
You should refer to the local codes in your area first. However, generally speaking you should probably look into having the pipe pitch corrected so your exhaust pipe can self-drain correctly.
-Trey
Hello,
I have recently had a HE furnace installed and while there is silicone on the outside of the exhaust pipes, I am noticing a bit of cool air on the inside, in addition to unwanted light.
Wondering if I can put spiral pipe wrap around the PVC pipes on the inside (in the hole of the foundation). It would be malleable to allow for the expansion of the PVC, but I am concerned that it may compromise the function of the pipes by causing additional condensation, or allowing the pipes to get too warm. The alternative was possibly expanding foam???
My thanks in advance,
KB
Can i add an extender to my furnace exhaust during the winter? The vent is currently 22 inches above our deck which gets a ton of snow during the winter. I am afraid that during the night a snow storm is going to block it. If not, what can we do to avoid this danger???
Hi Trey,
We live in northern ontario….we just put in a high efficiency furnace and the only place they could put the exhaust was through our deck. It stands almost 2 feet from the floor of the deck. Because we generally get a lot of blowing snow on the deck I am concerned with it becoming plugged. What can we do to avoid this….i was thinking of running an extension just for the winter…If this is doable, do you have any suggestions for the extender….something i can slip on and off?? Thanks….
hi Trey,
i have a Rudd high efficiency furnace mounted in our crawlspace at our cottage. it was installed in 2011, we have since done a remodel. the new contractor had to extend the current exhaust and intake pipes as we added on to the side of the cottage where they were vented. when it was installed in 2011 the contractor separated the intake and exhaust pipes by making the distance in height of pipes about 12 inches.which is code to separate the pipes. when the new contractor extended the new pipes they brought the exhaust and intake pipes at the same height and just put elbow fittings on the end. i am concerned about this as it could be a health hazard pulling exhaust air back in the intake pipe, the contractor tells me this is code now can you tell me what you think. thank you Dennis
Hi Dennis,
I’m not sure of the codes in your area, you’ll need to check on them
-Trey
I have a high efficiency furnace. During the spring a bird made a nest inside the flue from the roof of the house. I had the furnace guy out today he removed the nest from inside the flue inside the house. Is there a screen I can purchase to put over the top so birds don’t try to build a nest again. If so what is it called? And what size is it? Is it dangerous to block it with a screen?
Hi Carol,
Generally, it’s okay to put a screen over the furnace flue as long as it has large holes that don’t impede airflow. However, you should check with the local codes in your area to ensure that a screen on the furnace flue is okay.
-Trey
I have a crown boiler, with steel pipe that was coming out of the basement wall pitched to a 45 degree angle. I recently had some work done to wall outside for cosmetic purposes and the workers, added an elbow to the outside vent pipe so that the hot air moves away from the wall. Will this affect the boiler function?
Hi Marker,
You’ll need an HVAC technician to look at your specific setup to know whether that added elbow is affecting how your boiler functions.
-Trey
Hi Trey,
I have a high efficiency furnace and was recently told that I need to replace my pvc pipes as they are 1.5″ and code is 2″ diameter in Massachusetts. Is this correct?
Thanks
can you tie the intake and exhaust pipe on a he gas furnace together before it exits the house? I was told it just preheats the incoming air to the furnace.
Hi Bill,
I think what you’re referring to is a concentric exhaust pipe. Yes they can be used. In addition to preheating the air, they allow for only one roof/wall penetration to be made instead of two.
My PVC exhaust vent is located 3 feet above the metal hotwater vent on a sloped roof. When wind is from a direction where hotwater vent is venting into the furnace PVC vent.. could it cause a rather loud ignition after inducer fan has activated? Only seems to happen in mornings first run .. after furnace down over night calling for lower temp.
I’m having issues with my high efficiency furnace burners not staying on. The issue started when it got really cold here two days ago. The temperatures have been from -20 to -5 degrees Fahrenheit for the highs. The furnace flames fire up and then go out between 5-45 seconds after that. It’ll try to light 3 times before it’ll shut off. I checked and cleaned the flame sensor. I removed the flame sensor and it won’t stay lite for more than 3 seconds when I do that. So, I don’t think the sensor is the issue. Can the outside cold temperatures be causing it not to vent correctly? My furnace vent is pvc and vents out the side of the house. I’ve check for obstructions and there are none.
Hi Justin,
What kind of error code is your furnace showing after it tries to turn on?
Hi Trey,
I have a high efficiency furnace and my exhaust is coming straight out of the roof. Twice now my CO detectors have gone off and after 4 HVAC companies have inspected my furnace no one has found anything wrong. Is it possible that I may need to put a couple 90’s on the exhaust to keep rain and snow or debris from possibly getting in? Maybe that is what is causing the CO? and if so should I also install a screen?
Hello Trey,
Had an HVAC tech here today who mentioned the PVC reducer on the exhaust flue (4″ to 3″) needs to be “flat” on the bottom of the interior of the PVC piping. Said that our “mushroom” is not flat on the inside and condensate will accumulate in the depression and can “spill over” into the furnace causing problems. The tech said the correct (to code) transition has a flat side on the inside to allow drainage of the condensate. He proposed making the correction for around $500.00 Does the PVC piping have to have a flat side on the interior? Does that pass the sniff test? Second, the cost to replace the section of PVC piping for $500.00 seems excessive. Any insights are appreciated.
Does it matter that my High efficiency furnace exhaust pipes are located directly behind my A/C unit outside. If I run my A/C will it suck in the fumes that are being exhausted from the furnace exhaust pipes?
gENERALLY WHAT DO FURNACE PIPES COST TO HAVE REPLACED?
My exhaust pipe on the roof is sightly bent. Will this create a problem. Trey
Installing a high efficiency gas furnace. Is it ok to vent it (PVC) into the chimney previously used by the old oil furnace?
Please consider modifying the paragraph containing “sloped towards the furnace”. Please instead indicate which end is higher/lower.
“Sloped towards the furnace” may mean different things in different regions of the country or different things even within a company. (I.e., identifying a slope as being upward or downward to or from a destination is possible.)
Consider something like:
“When a metal pipe is allowed by local requirements, a 12:1 slope may be be required. In any case, the metal exhaust vent pipe height will increase as it runs from furnace to the outside.”
The meaning of “sloped towards the furnace” may be obvious to the knowledgeable but not to others.
Great web page.
Thanks!
I have old standard furnace with little leakage on pipe attached to oil tank .. I smell oil in home now and then with and without furnace running.. what can I safely do to stop
Hello, Concentric pipe that I just seen a few drops of water on the insulation below and a bit on the exhaust portion of pipe My question is whether or not the exhaust side needs to be insulated in the attic. I would say the attic is already on the warm side as its small and has a lot of duct work (wrapped) . If not it could be coming from roof or on one of the fittings. Thx
Hello, I have a high efficiency furnace that has intake and exhaust pipes exiting over my walk out basement door. Ice is forming on the concrete walk out and can rise to be 8″ high and 4″ in diameter. This will prevent the storm door from opening. Can I add a 90 degree pvc (angled at 45), and a small piece of straight pvc to divert the water away from the concrete? Thank you
How far apart should the intake pipe and the exhaust pipe be? Mine are only 6 inches. This seems to close.
Both pipes exit the house on the North side close to the air conditioner. I think the intake might be drawing in some of the exhaust fumes, but it seems I am the only one that can smell it.
Hello, I have a high efficiency furnace with the intake and exhaust pipes as a standard installation. Works great in summer but blocks quickly with snow in winter given drifts. Is it possible to extend the pipes upward to a height that will prevent blockage, say a few feet. Getting there to shovel is not easy.
Thanks