# Furnace filters turn black quickly



## bobinphx (Nov 25, 2011)

ok.. first off I am not a pro. I have worked on many many ac systems for friends and family, not to many furnaces and no oil type. with that said, here goes. 

I would suggest that maybe the black is combustion particals from the oil burning heater exhaust. so if we take that idea and run with it, where could it be comming from? 

I suspect that something after the burners is leaking. 1989 is getting a bit old, so I think that maybe having the heat exchanger checked by a pro would be a good first step. The heat exchanger contains the flames and the exhaust gases on the inside and allows your inside home air to circulate aound the sealed outside area and pick up heat (really hot heat!!). So if there is a crack or a leak, soot could be comming out, as well as carbon dioxide, then circuilating in your home. 

Once the exhaust gases leave the exchanger (cooler now), they enter the exhaust ductwork or flue or chimney or what ever name you want to call it. The exhaust gases may contain soot and for sure have carbon dioxide, as well as some condensation vapor. so I would also check for leaks in exhaust ductwork. The exhaust ductwork may also have rotted from the inside due to the condensate. so it may be hard to find. again a pro could help find this with a co detector and other tools. 

an other idea is that your furnace maybe using inside air for combustion. That air has to come from somewhere else, thus the system may be pulling air that is "dirty" through the cracks etc of your home. your hvac system would not pull in outside air (normally), so this might be the why you dont have dirty filters in the summer. I would do a caveman type test and crack open an outside door with the furnace off and see how much air is moving in or out. Then turn on the furnace and crack the same door and see if there is an increase in air flow (ie negative air pressure indoors). You can use tissue paper to help see the air movement, both on and off. 

Other here have much more experiance... I dont !!!!! 

hope this helps.


----------



## tls1 (Aug 8, 2012)

Hi,

Thanks for the info... I think condensation and age might be the culprit! In the rear if the furnace in the return area there is the blower at the bottom, above that are the filters, above that are the exhast tubes carrying the smoke from the chamber to the exit of the furnace. There are 5 of these tubes connected to square piece. It's hard to describe what they look like. They are used to prewarm the air. Anyways the do have some visible rust. Maybe there is a hole somewhere allowing exhaust to escape. its a very powerful fan back there...would not take much!

Also, note our home CO2 detector is rock solid at zero located in the main area of the main floor! Not near any duct or return.

I will post a pic of the rust part.

Thanks all!
terry


----------



## Missouri Bound (Apr 9, 2011)

Does this furnace also supply air conditioning, and is this black filter issue prevelant when cooling?


----------



## handyman_20772 (Jun 28, 2006)

Is there a opening on your return within 10' of the furnace itself? It's looking for makeup air when the furnace is running and you may have some backdrafting going on.


----------



## tls1 (Aug 8, 2012)

We have heat pump and it never happened with AC or heating during mild conditions. Speaking on the phone with our contractor, he thought the door to back of the furnace was not closed properly and exhaust was being sucked in. But that is not the case. 

There is no return in the basement level. However I know there are leaks in the returns, because when the blower is running, it can suck the basement door closed. Heating or cooling. I added a vent to the basement door to lessen the effect.

thanks!
terry


----------



## beenthere (Oct 11, 2008)

Do you burn candles.


----------



## tls1 (Aug 8, 2012)

only on birthday  sadly a lot of them ...

kidding... we rarely burn candles...or anything else... no fireplace, etc...

thanks!
terry


----------



## bobinphx (Nov 25, 2011)

you might want to take a look at the specs for your co detector. I have read that they are not so great at low long term levels. 

here is a news report... for what its worth. 

http://www.myfoxtwincities.com/story/20048296/are-carbon-monoxide-detectors-sensitive-enough


----------



## hvac benny (Dec 29, 2009)

bobinphx said:


> you might want to take a look at the specs for your co detector. I have read that they are not so great at low long term levels.
> 
> here is a news report... for what its worth.
> 
> http://www.myfoxtwincities.com/story/20048296/are-carbon-monoxide-detectors-sensitive-enough


That's to reduce nuisance calls. CO isn't the only thing that sets off CO alarms. The best way to avoid CO exposure is having your appliances properly maintained (beyond just changing the filter). CO alarms are a last line of defense.


----------



## jagans (Oct 21, 2012)

Is your furnace an updraft, or downdraft type. The reason I ask, is that the filter (s) need to be on the incoming side of the blower. You said your filter is above your blower?


----------



## tls1 (Aug 8, 2012)

I'm not sure if it's updraft or downdraft...but... here a drawing attached similar to mine.

On another note, my contractor told me that while the exhaust system may have a leak, burning oil does not produce carbon monoxide (CO). It produces carbon dioxide (CO2). Too much will still kill you :huh:.

However, he also asked if there was a funny smell like buring rubber (or burning anything)... no there was not. He's coming Wednesday morning to check.

thanks!
terry


----------



## jagans (Oct 21, 2012)

This illustration is not very good, as it does not show incoming return air, outgoing plenum etc. but good luck with your problem. It sounds like dirty jets and a breached heat exchanger.


----------



## tls1 (Aug 8, 2012)

the cold air return is on the right of the drawing.

the exhaust flue prewarms the cold air . Then it is filtered, then to the fan, then to the chamber and up the left side into the house.


----------



## beenthere (Oct 11, 2008)

That pic is of a low boy, up flow.


----------



## how (Feb 26, 2011)

Turn off the power/ open up the fan compartment/ check all sides of the flue pipe inside the fan compartment with a trouble light and a mirror for cracks or rust/ check the holding sleeves on either end of this flue pipe in the fan compartment for black exhaust markings.


----------



## old_squid (Oct 31, 2012)

Take a clean piece of white paper, rub your finger on the filter where it's black, rub the black onto the paper, does it smear like it might be oily or act more like dust? Is it hard to wash off your hand?

Do you find this "black" anywhere else in the house? Time for the white glove test.

If the stuff on your filter smears, appears oily or is hard to wash off your hands then you're somehow getting exhaust products from your oil furnace into the air you breath in the house. If you only find it on the filter and no where else in the house I suspect there is a hole or leak in the pipe shown on your diagram just above the filter that goes to the chimney. If you find it all over the house then the hole or leak could be anywhere in the furnace.

Either way you need an oil furnace tech out to check things over right away to find where the crack/hole is and see if it's either something that just came apart and can be fixed or you might need a new furnace. The situation is dangerous for many reasons and should be resolved asap.

And the person that told you that oil furnaces don't create CO is .......... an idiot and shouldn't be the one working on your furnace or anyone elses in my opinion.


----------



## tls1 (Aug 8, 2012)

Hi all,

So the contractor came by today... again he said that oil furnace do not create CO (only CO2 Carbon dioxide)... I will interogate him on that!

Anyways, he took apert the back of the furnace and checked and there were no leaks. he also replaced the nozzle and tuned the air intake for optimal clean burn.

He added some cement to where the tin exhaust enters the cement wall for the chimney. There were some gaps and he felt some smoke might be getting back into the house and being sucked into the furnace. The cement wall is around 2-3 feet from the return. We also put some aluminum tape around the filter door to keep it sealed. 

We discussed the cost of replacing the equipment and he said I should keep using the machine until it dies.... It's paid for... why spend the $$ if you don't need to.

A new electric furnace 23KW/1HP is around 3K$ + tax including removal of old furnace and tank. And add 240V wire (20$ per yard) and breaker.

New oil furnace + tank + chimney liner is about $6K,
New dual energy oil + electric furnace + tank + chimney liner is about $7500 + 240V wire. 

Thoughts ?
Cheers!
Terry


----------



## beenthere (Oct 11, 2008)

Adjusted for optimum clean burn? How did he do that if he didn't take a smoke reading and do a combustion test. 

Carbon Monoxide is a by product of incomplete combustion, and can occur with any thing that burns. He may be use to Fyrite kits. Which only measured smoke, draft, flue temp, and CO2.


----------



## JScotty (Jan 14, 2013)

tls1 said:


> Also, note our home CO2 detector is rock solid at zero located in the main area of the main floor! Not near any duct or return.


 As the post above this points out Carbon Monoxide is created anytime you don't have complete combustion. However assuming your furnace is properly set up even with a massive hole in your heat exchanger your CO detector will never go off. Because it only creates CO if it isn't burning right.

So just because your detector isn't going off doesn't mean your not leaking flue gas somewhere.


----------

