[TBaker]

I have a 13 year old Carrier gas pack that stopped working last week. The thermostat works and the unit will kick on but no heat (or any air period) comes up in the vents. The unit is working as it is kicking air out its side vent. I had a technician come look at it today and he said he had not yet found the cause but that he did find that my heat exchanger has a severe crack (it does, he showed me with a mirror). Though the crack would not cause it to not work, he said this is very dangerous as it lets carbon monoxide into the house. He shut off the gas and said I could either replace the heat exchanger for approx $1800 or just replace the entire unit because of its age. So I have two questions: 1) is it true that it's so dangerous to use it with the crack? And 2) If I choose to do nothing and keep the heat turned off, can I still run the A/C in the summer time without that crack having any impact? Winter's almost over here in NC and I can survive without heat until next year (when I may actually have $4000 for a new one) but the summers are brutal. Thanks.

Teri

[rickdb1]

Do not use the furnace. It can and will kill you. It would work for AC with no problem...

[letmetellu]

It is very dangerous to use a furnace for heat that has a crack in the heat exchanger. I know that there are a lot out in the country that do have cracked heat exchangers that the people don't even know about. But you can bet that they are suffering from the effects of being in the house all winter with even a small amount of carbon monoxide. Carbon monoxide is an accumulative thing that as you breath it in it stays in your system and each day you add more.
It would be OK for you to use the blower on your furnace to supply the air for you Air Conditioner, just make sure that the gas is turned off and the supply stop.

When you get ready to replace your unit get at least three bid, and make sure one of those bids is from an independent dealer, with a small business.

[labman]

Yes, it is dangerous to use a furnace with a cracked heat exchanger. I would take look at the blower before the heating season is upon you. It the blower isn't working for the furnace, it may not work for air either. Try the on position for the fan. Usually it and the A/C use the same motor winding and relay separate from the heat.

[hvac1000]

DANGER. CO poisoning is a killer. DO NOT USE THE furnace for heat. The heating news is full of deaths caused by conditions like your furnace is in.

[Blakester]

I have a 13 year old Carrier gas pack that stopped working last week. The thermostat works and the unit will kick on but no heat (or any air period) comes up in the vents. The unit is working as it is kicking air out its side vent. I had a technician come look at it today and he said he had not yet found the cause but that he did find that my heat exchanger has a severe crack (it does, he showed me with a mirror). Though the crack would not cause it to not work, he said this is very dangerous as it lets carbon monoxide into the house. He shut off the gas and said I could either replace the heat exchanger for approx $1800 or just replace the entire unit b/c of its age. So I have two questions: 1) is it true that it's so dangerous to use it with the crack? and 2) If I choose to do nothing and keep the heat turned off, can I still run the A/C in the summer time without that crack having any impact? Winter's almost over here in NC and I can survive without heat until next year (when I may actually have $4000 for a new one) but the summers are brutal. Thanks.

Teri

I have the same issue. Look at other vendors. My first quote was 1500, and I have found someone that will do this for 900. I am still looking, and you may be able to locate the part online, and have someone (a friend that knows how to) install the part for you. My systems part alone is about 600. Take care, good luck and don't let them rip you off!
SOME are warranted for the life of the system, so ask the HVAC vendor that specific question. They sometimes will charge you and turn in the part as a warranted item and collect twice... Shady, Huh?
Blake

[letmetellu]

The part about having a friend install a heat exchanger for you I would think long and hard before I let someone that was not trained do one for me. I have been to different schools and I have installed many heat exchangers. After I install one I can't sleep good for several nights thinking over and over all the steps I followed to make sure I did it right.

One person did mention the warranty on the heat exchanger, now this is something that you should explore. A furnace has several heat exchangers, depending on the BTU of the furnace so if you have one cracked then that is all they will replace but the others are the same age as the one replaced so it makes you wonder is it is a good idea to just replace the cracked one. And actually the cost of labor for doing three is not going to be much more than just the one. Just something to think about.

[NorthernHeat]

This one never fails to amaze me. The furnace is 13 years old, so are the limits, motor/s heat exchanger, single wall flue pipes, pressure switches, circuit boards, get the drift? A new furnace costs how much?? 4000 dollars for the top of the line 10 year part and labor warranty. Average life of a furnace is 20 years. Average service call is 320 dollars, regular rates. So you put 800 in it now, 350 in it 2 more times in the next 5 years, get tired of the dependability, or you decide it is time to replace it. Will it still cost 4000 dollars to replace?

Here are a few facts you should consider too. Not all heat exchager designs are good. Good designs fail for 2 reasons, gas pressure was to high or air flow was insufficient. Usually due to ductwork that is to small, furnace is just to big, poor maintenance, dirty restricted filters.

On the rare occasion the whole furnac design was poor and didn't suroud all sides of all the cells with air. These models are easy to find the cracks in, it is always the to outside cells nearest the cabinet.

If you had a '92 Taurus would you put a new engine in it? Yes, I'm venting, but I really think unless your financial situation is very bleak, doing a heat exchanger is never a good pay off.

[T-Top]

This one never fails to amaze me. The furnace is 13 years old, so are the limits, motor/s heat exchanger, single wall flue pipes, pressure switches, circuit boards, get the drift? A new furnace costs how much??? 4000 dollars for the top of the line 10 year part and labor warranty. Average life of a furnace is 20 years. Average service call is 320 dollars, regular rates. So you put 800 in it now, 350 in it 2 more times in the next 5 years, get tired of the dependability, or you decide it is time to replace it. Will it still cost 4000 dollars to replace?

Here are a few facts you should consider too. Not all heat exchager designs are good. Good designs fail for 2 reasons, gas pressure was to high or air flow was insufficient. Usually due to ductwork that is to small, furnace is just to big, poor maintainance, dirty restricted filters.

On the rare occasion the whole furnac design was poor and didn't suroud all sides of all the cells with air. These models are easy to find the cracks in, it is always the the to outside cells nearest the cabinet.

If you had a '92 Taurus would you put a new engine in it? Yes, im venting, but I really think unless your finacial situation is very bleak, doing a heat exchanger is never a good pay off.

I agree with northenheat. What happens next year fan motor, gas valve or compressor? Look at the odds it will happen.

[schnidly]

Heat exchanger cracks is a long standing scam. The furnace box is under negative pressure if the flue in not blocked. So any cracks in the heat exchanger would only increase the amount of heat loss out of the house when the furnace is off and if the furnace was on flue gas intering the house would be as likely as a fish swimming up Niagra Falls.

[NorthernHeat]

You are so wrong it is scary!! Natural draft in only under a tiny fraction of an inch water column of negative pressure. Do you know what a venturi is? How is it so many people get hospitalized due to CO poisoning from their furnace? Why is it a CO detector can detect a cracked furnace? Why is it I have a friend, who with his wife, got poised by a 16 year old 90% furnace and barely made it to the phone for help?

[nol1032]

"Why is it a CO detector can detect a cracked furnace? Why is it I have a friend, who with his wife, got poised by a 16 year old 90% furnace and barely made it to the phone for help?"

Probably because they did not have CO detectors in their home.

[Gusiscrabby]

Schnidly has it right. You guys who don't understand air flow might want to pay attention and quit frightening your customers.

Any furnace with a standard blower, clam-shell or tube heat exchanger and an a-coil on it isn't going to directly put CO into the house air stream. Period. I don't care if you cut the tops off the heat exchanger cells.

The blower positively pressurizes the inside of the furnace cabinet from .5" water column to 2"WC depending on blower capacity, cabinet structure and a-coil resistance.

Even with 1/2" holes drilled in the top, back, or sides of a heat exchanger, AIR ALWAYS flows INTO the heat exchanger from the blower stream. There is NO way air from inside the heat exchanger is getting out and into the blower indoor air stream. Even when the tubes on a round-tube heat exchanger break from their welds at the top of the bulk head, air moves from the furnace INTO those tubes and plays hell with the burners.

Don't take my word for it. Try it yourself.

Someone mentioned venturi effect. Great idea except the venturi effect isn't in play when there is static pressure in the furnace cabinet.

Now, here is a caveat to be aware of. If you do these tests on a furnace but don't put an a-coil on it, you might be able to get CO (or air from inside the heat exchanger) to be pulled into the blower air stream. Since there is no static pressure being created inside the furnace cabinet, the venturi effect might work.

I've not tested high-efficiency secondary heat exchanger coils, but I suspect the situation is the same.

Anytime I've found CO in a structure, it has always been because of a combination of problems. Most of the time the flue is blocked or partially blocked. Sometimes it is due to flue back draft because of other fans or appliances running in the house. Eventually the furnace starts burning its own flue gasses. In every case the CO around the furnace gets sucked into the return air through cracks, open return-air headers and around the air filter and that is how it gets into the house.

My problem with the whole deal is every body jumps on a heat exchanger crack or a little hole, but doesn't adequately check the flue for capacity and draw, doesn't find out about other appliances and fans in the home, and may not be paying attention to free-air space and combustion air available to the furnace. To top it off, you'll reg-tag and shut down someone's furnace over a 3" crack in the middle of winter. And you know that doing this might force them out of their house, risk plumbing freeze ups and push them into a purchase.

[Joe7411]

Everybody is saying that a crack is dangerous; I think I understand your position but need to hear more. Would it be possible to expand your comment?

[Joe7411]

I have the same issue. Look at other vendors. My first quote was 1500, and I have found someone that will do this for 900. I am still looking, and you may be able to locate the part online, and have someone (a friend that knows how to) install the part for you. My systems part alone is about 600. Take care, good luck and don't let them rip you off!
SOME are warranted for the life of the system, so ask the HVAC vendor that specific question. They sometimes will charge you and turn in the part as a warranted item and collect twice....Shady, Huh?
Blake

I was just told that my heat exchanger is under warranty and will be replaced $0 but they want to charge me $1800 labor. Can I get the free part and find another expert to install cheaper?