Cracked Heat Exchanger

[Big Giant Head]

This is about a Bryant gas-fired downflow forced-air furnace, about 20 years old. It sits atop the A/C evaporator box.

It's the kind where there is an inducer (exhaust) blower. The inducer function gets proved via a pressure switch, sends power to the pilot valve and a thermostat switch heated by the pilot which when cold sends it a spark generator and when heated sufficiently, to the main gas valve.

I was trying to run down a problem that I think stems with that pilot t- switch (or maybe with the pilot flame itself) as the main gas frequently gets cut off while heat is still be called for. It keeps shutting off then quickly restarting. I don't know if that issue is related to what I discovered.

The burners are like four blow torches feeding into the heat exhanger.

Around the exchanger inlet by the third burner, I noticed some cracking and burned metal.

I thought uh oh. This could be bad.

So I ran the blower alone to check it out. As this is a downflow, the blower is blowing down through the exchanger and with the A/C coil under acting as a resistance, the air through the exhanger will be somewhat pressurized. With the blower running I put a lit candle near each entry into the heat exchanger. No sign of wind. No fluttering. Just a nice gentle pull on the flame *into* the HE probably because it was still hot and creating a slight chimney effect.

Whew, I thought.

Then I went back to my issue. While watching the burner operate I noticed that the flame on the third burner which started out looking like the others started to change a bit. I'd seen this difference before and thought maybe the gas flow was slightly impeded so I made sure the orifice was clear. Well, I started staring into the heat exhanger opening that it was feeding into and started seeing weird motions of the gas flame. I got to thinking that the HE might have a crack that is opening under heat.

So I immediately killed the heat, kept the blower going and got the candle and sure enough the flame blew around a little bit when held by the third opening. I think there is little doubt that there is a heat exchanger crack.

So I need a new furnace. Right away.

I know this cannot be ignored. The question is whether I need them out ASAP in the morning or I have a couple days to weigh proposals.

Before you answer:

Because this is a downflow and because the A/C coil means the HE is pressurized on the air side, it's not going to suck in fumes through the crack. In theory it could blow fumes out of the furnace into the room but I think I would see that when the flame is no longer being drawn into the HE. The crack is small enough not to overcome the inducer and general upflow of the hot gases.

There is a CO detector just outside the furnace closet.

Is this a busy time for HVAC because it's cold or a slow time because people are more concerned with Christmas shopping?

[micky]

If this is true, and I'm not saying it's not, wouldn't it be best for everyone to always use a furnace with the blower blowing into the HE area? Yet I know they're not all like that.

(I don't think downflow specifically means what you say, or the placement of the AC coils, but the fact that the blower blows into the HE does seem to mean it won't suck fumes in. Others blow from the fan to the rooms, meaning they are sucking from the HE, right?) .

I'm going to need a new furnace someday, and I would think one that did that could fit where the current one is.

fwiW, about 10 years ago when I got my first CO detector, or when I was starting to wonder if it was still good, I called its 800 number, maybe First Alert, and asked a few questions not covered in the instructions.

One was whether I could put it right by the furnace. (I have no closet. I had in mind about 3 feet away, or for a few minutes 8 inches away) and she said not to. The trouble is she was probably reading from a script. I think I asked if it would overload the detection mechanism and ruin the CO detector, and I doubt she knew the answer to that, but even if she did, her answer didn't cover it.

Hmmm. Maybe your instructions include just outside the closet. If mine had, I would have fogotten by now.

Then comes the question, is that the location of first and greatest CO? If the ducts are leaking, maybe, but otherwise, wouldn't it be the closest air output duct to the furnace.

[Ed Pawlowski]

If you called the gas company, they would tag it out of service immediately. I honestly don't know if you have a few days or not, but I'd call someone first thing in the morning.

One of our tenants in our building at work is a 3 man HVAC company. They have been busy for the past month or so. First couple of days of summer heat or winter cold gets them hopping for a few days, but this is now more normal busy as opposed to emergency.

[Shadow]

Good for you. Any chance you might post the serial number ? I've been trying to register mine for ages. TIA ;) []'s

[trader4]

One thing that's not stated is where it is, how cold it is and how much the furnace really needs to run. If it were me, I'd get it replaced ASAP, but I would still get several quotes. In the mean time, for a few days, I would buy an additional CO detector for the living area and I would only run the furnace under supervision. Meaning fire it up a few times during the day while you are there. And I wouldn't run it at night, when going to sleep, etc.

[trader4]

If what's true? That he has a blower that forces air past the heat exchanger? That it pressurizes it? Even if they are not all like that, everyone I've seen, and that's a lot of them, have the blower forcing air into the heat exchanger, not pulling it out.

It may exist, but I've never seen a furnace like that.

[Big Giant Head]

It's cold enough that it needs to run regularly. But who knows how long it's been this way. Nevertheless, I will not wait on this. I will visit a couple of vendors we have used in the past get some ballpark pricing information about makes and types and invite them out to see and give a formal quote.

I think the possibility that it could suck fumes through the crack is almost nil especially with an A/C coil (and probably a dirty one at that--- more dirt gets past the filters than one would expect) providing resistance and causing the HE to be pressurized on the air side. So if the crack suddenly enlarged massively it would blow fumes out where the flame is going in. At present there is not even a hint of that. The difference in the flame that I noticed is extremely subtle. What I could see looking into the HE (and that's not to say that there's stuff I am not seeing) is putting just a little wisp of flicker in the flame at the bottom of that segment.

With burner off and inducer stopped, while the HE was still hot, the candle test I described was just a slight flicker; enough to show there was a problem. Bet if I powered up the inducer it would suck the candle flame right in.

But a couple more CO detectors might be cheap insurance.

In the meantime I guess I will try to find original paperwork and see if by some chance there was a lifetime HE warranty. Not that it would help without labor. I highly doubt it anyway.

BTW, is there any type of furnace in this category (gas, downflow) that is quieter? This machine replaced a 1957 Rheem with traditional cast iron burners, continuous pilot, which barely made a sigh while running; only the blower made noise when it came on. The new high(er) efficiency (by 1985ish standards) with inducer, blow torch burners is so loud on burners alone that one barely hears the increased noise when the blower kicks in. It lives in a hall closet so it was a revelation how much noisier it was. One gets used to everything but it would sure be nice to get something a few dB less.

snipped-for-privacy@> >> On Sun, 01 Dec 2013 01:04:42 -0600, Big Giant Head

[micky]

Are you going to tell them you need a new furnace, or are you going to call their repair division and see if he says you need a new furnace?

If you tell them you need a new one, that's what they'll sell you, even if some smaller repair will fix it.

How old is your furnace?

IIRC, you say you cleaned that jet, but did you do a good job? Is it possible the hole is too big now?

I don't know anything about furnaces beyond my previous post that relates to your particular problem. Is the test with the candle the industry-approved test, or one of your own? What is the industry test? Maybe a repair guy could do that for you?

[mroberds]

For what it's worth, when I bought the house I live in now in 2009, the furnace that was in it (dating to either 1969 or the early 1980s, I don't remember for sure) had a cracked heat exchanger, per the home inspector. His advice was that if I wanted to run the furnace during the day while I worked on the house, that would be OK, but not to sleep here with the furnace running.

I think the previous owner knew he was living with an old furnace, because the house was generously equipped with smoke and CO detectors.

All of the houses I have lived in have had the furnace out of the living area, so I haven't paid too much attention to how much noise they make. I recall the new gas furnace that my parents got in the mid-90s being louder than the mid-60s original when running, but not so bad I couldn't stand it.

A new high-efficiency furnace will probably have a "sealed" burner box, which IMHO cuts down on the noise from the burner a little bit. It will also probably have the two-3"-PVC-pipes intake and exhaust system, rather than the one-6"-metal-pipe exhaust, so you might be thinking about where you want the pipes to go.

There are some tax credits available for furnaces and air conditioners of a certain minimum efficiency. Right now I think they expire at the end of December 2013. The HVAC companies will know about them and will give you the right paperwork for it. I got the 2009 version of those credits; the installer wrote me a letter that basically said "your model

123 furnace and model 456 air conditioner that we installed at 789 Foo Street on 31 June 2009 meets the requirements", and if I remember right, I included one extra form and a copy of that letter with my tax return. has the current specs.

Matt Roberds

[Big Giant Head]

I think a bit of both. I will inquire about getting a new furnace because the old one is having issues which is true. And then mention my diagnosis and how I came to my conclusion. I certainly welcome having a pro check it out before buying a new one but I don't want them getting into a panic and wanting to set me up with whatever they have sitting there if a more appropriate unit takes one more day. I would explain why I feel safe to operate it a few more days. They can agree or disagree but I tend to think that potential liability issues would have them insist that I turn the thing off immediately.

Quite true. Who knows...maybe they will say this model had a HE that has 4 separate sections bolted together and the bolts need tightening. But I seriously doubt that.

I have a feeling that once I tell them how I tested it they're going to just say, yup, cracked HE...get a new furnace. No need for more tests. And while that *is* probably the right answer, there's no way to know if they aren't giving it because that lets them sell a furnace AND agree with the customer and make the customer feel smart about averting a serious situation.

I was thinking 20+ years but I saw something on it that said 1985 so more like 28. Will know for sure when I find the paper work but close to 30 is probably about right.

Nah...the flame did not change in size. I only prodded it with a wire and then put a canned air tube against it. The business about the flame changing shapes as things warmed up is what caused me to look more closely and see the oddities within the bottom part of the HE, probably where air is getting in and then do the candle test over again while the HE was hot.

I don't know what test pros use but I think with blower on, burner & inducer off, holding a candle in front of the one HE inlet and seeing it get subjected to air movement is indicative of something.

Can a tech tag something out of service to where it would be illegal to then use it?

[trader4]

Good grief! He stated it's a 20 year old furnace with a cracked heat exchanger. What simple repair is gonna fix that?

WTF does it matter? He has a CRACKED HEAT EXCHANGER.

Good grief.

[Big Giant Head]

I think he was just wondering if something I did caused the flame to look different. But that's only what drew my attention. The difference in the flame was so subtle you'd barely notice. Not sure how to describe it since the shape remained the same. Maybe like the flame seemed a bit hollow compared to the others. But what I saw the flame doing in the bottom of the HE is what caused me to pull out the candle for a 2nd test, one while the HE was still hot.

Anyway, it does sound like you're satisfied that my test did indeed confirm a bad heat exhanger. Gracias.

[bob haller]

price a brand new GOODMAN with A/C

very affordable works great:)

[Tony Hwang]

Hi, I thought heat exchanger warranty is very long.

[micky]

Thinking it's a cracked heat exchanger doesn't mean it is a cracked heat exchanger. Duh.

Do you believe everything you think?

He's one guy who likes to show off. Don't take him too seriously.

You can always do that at the end of his visit, after he's told you what he thinks.

First I would want his diagnosis and you can ask him how he reached it. You can always mention your diagnosis and your way of reaching it at the end, too, but if I were you I wouldn't just say how you reached your conclusion but ask him what he thinks of your method. His answer might be revealing.

You're talking about something related, the part about blowing out combustion air rather than sucking it in. Since that is directly related to cracked HE, I wouldn't bring that up until last either. That way YOU won't be causing his panic if there is any. He and his own diagnosis will be causing it. If not his own diagnosis, maybe not a real pani but his desire to get you moving, so he can sell a furnace.

But you're going to let 3 people come out before you buy, so you'll have the chance to hear three opinions, if you don't tell them first what you think it is.

I doubt he would do that. He might give you the choice of going a day or two more without heat versus getting what he might call the less good furnace! If you are without heat, don't try heating the house from a gas stove, CO risk iirc, but you can warm it up substantially by boiling water on the stove. Boil a great big pot until it's almost dry, the humidity will go up**, and the house will feel 5 degrees warmer, or more. Run an all hot shower into a stoppered tub, with the bathroom door open and that will humidify the bedroom area even faster. Remove the soap fromr the soap dish or it will be washed away, and don't let the tub overflow. The overflow hole never seems even nearly fast enough. A couple people here claim that boiling water, etc. does't work, but it does, very well.

An electric blanket will keep you warm sleeping and more clothes will keep you warm when you are awake. My blanket goes up to 9 but I've never had it above 2.

**Houses tend to be dry in the winter, which makes people feel colder (summer or winter). Even if you have a humidifier on your furnace, since your furnace wouldn't be running in this scenario, neither will the humidifier.

Then what makes you think they will agree with you? And much more important, what has this got to do with whether you give them your opinion before they give you theirs?

I rarely have anyone work on my house -- it doesn't need anything or I can do it -- but I've had at least one crooked chimney sweep who low-balled on the cleaning price and then came to my house and claimed I needed 800 dollars of new flue between my furnace and chimney, just about 14 feet or less.

And I have a friend, not a sweep, who has told me how he overcharges people who don't know better. I didn't know what to say and I hope he didn't notice I didn't say anything.

Make them tell you what you need. Don't give them big ideas. It's going to be easy for even a partly honest company to say you need a new furnace based on the age of yours alone. It will be easier yet if you say you think you do too, and easier still if you say that before they've given their opinion.

Maybe it will turn out in this case that you do need a new furnace, but you have to abandon your desire to tell a repairman what you think the problem is**, especially when the solution to that problem is the most expensive fix out there. **It sounds a little bit like you want to show him how smart you are, so that he can confirm it. Whether you're smart or not, now is not the time for that.

Auto repair is another place where people, especially men, including me, have an idea of what they think is wrong and they often tell the repair guy what to replace, instead of waiting for him to tell the customer what he thinks needs replacing.

[hrhofmann]

Micky is right, don't tell the repair guys what you did until AFTER they look at the furnace and tell you what they think and why. You'll learn a lot more by doing it in that sequence!

[trader4]

He provided reasonable evidence that it is.

It's not what I *think*. He provided a deductive process.

I like to show off? As opposed to what? Give stupid answers, like you? You implied that a furnace where the blower forces air through the heat exchanger, applying positive pressure, instead of sucking it through, is an oddity. I've seen a lot of furnaces and have yet to see one designed that way. Not to say that they don't exist, but your incredulity about the fact that he has a furnace where the house air is blown throught the heat exchanger, says you don't know WTF you're talking about.

Maks sure to tell him micky finds it odd that the air handler blower forces air throught the heat exchanger, instead of applying negative pressure. I'm sure that will impress the tech.

He's not talking about blowing combustion air. He's talking about the air handler blowing air. Try reading what he wrote.

Since that is directly

What nonsense. Rest of nonsense deleted.

[trader4]

That's what companies are counting on. Dummies like you. It's a 20 year old furnace. How long is "very long' and even if the part itself is covered, by the time you factor in that labor rarely is included, nor are other charges like miscellaneous parts, the rest of it is still 20 years old, etc. it rarely makes sense to put a new heat exchanger in a 20 year old furnace.

[Stormin Mormon]

you did until AFTER they look at the furnace and tell you what they think and why. You'll learn a lot more by doing it in that sequence!

"It's cold in here. Do you think it might need a new thermostat" is a good way to start with the call.

Went to a couple friends, one time. House was hot. Find out they were on their 4th thermostat, and hadn't got it fixed yet. Yep, fourth, 4th. Wow.

[jamesgang]

They all force the conditioned air past the heat exchanger for just the safety reason you figured out. I'd start shopping now for a new furnace since your's is that old.

Not that I'll take responsibility for what you do about the old one but I have seen heat exchangers in such bad shape that when the circulation fan started up it blew the flame all over the place.