Cracked heat X ????

[CAtech1986]

not to be argumentative but tell me what a "tight" crack is. and in what case have you found this type of crack and your monitor didn't get it? if so what numbers were you reading? what type of furnace? to me a crack of any size is going to show up if it is in the airstream. most hvac guys dont use monitors anyway so i understand the skeptics

[Chuck]

not to be argumentative but tell me what a "tight" crack is. and in what case have you found this type of crack and your monitor didn't get it? if so what numbers were you reading? what type of furnace? to me a crack of any size is going to show up if it is in the airstream. most hvac guys dont use monitors anyway so i understand the skeptics

I use a CA on every furnace I work on. Many many times I have found cracks in heat exchangers that showed zero change in O2 or CO when the blower starts.

One particular model that comes to mind is the Lennox Duracurve heat exchangers. Every time I have found them cracked I have found it visually and they are always in the back on the first curve. They are never IME leaking air, at least not enough to pick up on an analyzer.

If you are relying on only a CA to find cracks you will miss over 80% of them.

[CAtech1986]

the lennox duracurve was a 80+ or natural draft?

[Chuck]

the lennox duracurve was a 80+ or natural draft?

You need to fill in your profile, are you a tech? I can't believe their are techs that have never seen a duracurve. They are all natural draft.

My post above is true of all furnaces, I just used the duracurve as an example.

[CAtech1986]

sorry just signed up. I am a tech. Been in the field five years. Frankly there are not a lot of natural draft furnaces left in my part of the country. most have been replaced. I still see them occasionally. i do enjoy being able to test seperate burners with the CA. Mostly oil, and induced draft i have experiance with. 90+ also of course. Had a Tappan a few years ago with 4000ppm in the exhaust before the draft hood with a draft of .07" i removed the draft hood completely and sealed it off. It is now using a 6" barometric and working great still today. other than that i reallyt don't see many nowadays. i would like to know how any furnace with a legitimate crack in the heat exchanger will not cause some kind of co action. if it is natural draft than the combustion chamber is subjected to a constant negative pressue. with any kind of hole in it the blower will cause some infiltration of what is otherwise supposed to be a sealed chamber. drastic changes... maybe, maybe not. 10-15 minutes of operation should reveal some sort of problem. especially as it gets hotter. O2 will drop, co will rise a classic venting diagnosis could become confused with a slight crack i suppose.

[Chuck]

Most of the time a leak allowing air to infiltrate the hx will cause the o2 to rise and the CO to fall when the blower comes on. Only a severe crack would cause the CO to rise.

Kudos for learning how to use a CA. I also regularly remove draft hoods and install barometric draft controls.

[CAtech1986]

wow! we should just start cracking heat exchangers and that will solve our carbon monoxide and venting problems!!!

[BigBacardi]

goodman with the rings(gmp)

lennox with the duracurve(whisperheat)

bryant (394 GAD)

oh how i lovew to do a tuneup on these....next thing u know the red tag comes out, and i leave the house with a $6000 job

o how i love these

[FrostyBeer]

wow! we should just start cracking heat exchangers and that will solve our carbon monoxide and venting problems!!!

uhh what?

[BigBacardi]

The best way to identify a cracked heat exchanger is with a combustion analyzer. with gas pressure set at 3.5 for natural and 10-11" w.c for lp. you'll notice a rise in co when the blower comes on. a drastic rise. you don't need to pull it out or anything. if it is rusting that indicates there has been a problem for a long time. What type of furnace is it?

the best way to identify a cracked htxchanger, is to be knowledgible in the specific models and where they crack, as i posted earlier....maybe wont get all of them...but using a CA is a poor way to find them...IMO

whisperheats are all(ok 95%) cracked...with no diff using the CA.....if crack aint open...

and IMO a crack is a crack is a crack. integrety is gone and unsafe to operate.

[JonesHVAC-R]

Curiousity getting the better of me..... how many of you use a CO meter (calibrated before entry to home) while doing clean and checks?

[Chuck]

Curiousity getting the better of me..... how many of you use a CO meter (calibrated before entry to home) while doing clean and checks?

All the top techs!

I carry a CO meter on every call to alert me if I walk into a dangerous space.

I do a combustion analysis on all gas or oil burning equipment I work on.

[JonesHVAC-R]

All the top techs!

I carry a CO meter on every call to alert me if I walk into a dangerous space.

I do a combustion analysis on all gas or oil burning equipment I work on.

Lol, I agree there! Leads to my next question...

How many of you when entering home and get a reading anywhere from 1-6ppm recommend replacing the furnace right there? (assuming the CO is coming from the furnace during operation)

[BigBacardi]

lol...loaded question

but yes... i do carry my co detector into every job.....responses from homeowners vary, but most are impressed

[Chuck]

Lol, I agree there! Leads to my next question...

How many of you when entering home and get a reading anywhere from 1-6ppm recommend replacing the furnace right there? (assuming the CO is coming from the furnace during operation)

If the furnace is spilling CO and causing house levels anywhere above zero then yes new is the first choice. Usually there is a repair option as well if the HO can't afford new. (unless the HX is cracked, which is almost never the cause of CO getting into the home)

[Mickandmousemechanical]

A rusted heat exchanger is not a failure if there is no "visible crack or hole".

What type of heat exchanger is it? When you open up the supply duct and look at it are the seams folded and welded. Because those particular H/E are tanks and seem to last. With a bore scope through the burner section they look cracked but indeed they are not.

I agree no visible crack or hole = No red tag

[martyinlincoln]

Curiousity getting the better of me..... how many of you use a CO meter (calibrated before entry to home) while doing clean and checks?

Got a perfect example of why that's important today. Lennox G20 that another company replaced the heat exchanger last year. It had the typical stress mark and rust line along the back but passed water test. Cleaned the burners,crossovers,pilot assembly and flame sensor then put it back together to get some flue gas readings. Stuck the probe in the flue and had 4.2% O2 and over 9000 ppm of CO,I know should have pulled the probe out way before that to save the sensor. Gas valve was cranked all the way in and reading 7.2", backing it out didn't change the pressure. Installed a new gas valve and made a new sheet metal flange that the bone heads left out. CO 14ppm with 7.2 O2 after fixes.

[JonesHVAC-R]

Got a perfect example of why that's important today. Lennox G20 that another company replaced the heat exchanger last year. It had the typical stress mark and rust line along the back but passed water test. Cleaned the burners,crossovers,pilot assembly and flame sensor then put it back together to get some flue gas readings. Stuck the probe in the flue and had 4.2% O2 and over 9000 ppm of CO,I know should have pulled the probe out way before that to save the sensor. Gas valve was cranked all the way in and reading 7.2", backing it out didn't change the pressure. Installed a new gas valve and made a new sheet metal flange that the bone heads left out. CO 14ppm with 7.2 O2 after fixes.

7.2"!! I had a tech once turn one down to 2" while I was away... I got back and asked why so low and he replied that is where it needed to be in order for the burners not to snuff out... Not quite sure what the hell he was thinking there... I told him to come with me and it turned out they weren't snuffing at all but they cutting out from the rollout sensor. Old Bryant 80% rooftop unit with just about everything rusting... gave them the option of repair or new unit, they took the new unit

[JonesHVAC-R]

If the furnace is spilling CO and causing house levels anywhere above zero then yes new is the first choice. Usually there is a repair option as well if the HO can't afford new. (unless the HX is cracked, which is almost never the cause of CO getting into the home)

Are you saying that if a heat exchanger is cracked that CO will not get into the home?

[bigtime]

Has anyone anywhere found a home with carbon monoxide in the living space, and the cause was a small crack in the furnace heat exchanger? If so Id like to hear the details.

On any residential co problem, Id put my money on a vent problem. Spend more time inspecting vents...