# Repair or Replace 13 yr old Furnace with Cracked Heat Exchanger



## Thor73 (Oct 23, 2011)

I have a 13 yr old Lennox G26Q3 high efficiency gas furnace that has a cracked heat exchanger. The heat exchanger is under material warranty still and I have a labor cost to repair of $1500. Would you recommend repair this furnace or buy a new one? 

Thank you for your feedback!


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## Doc Holliday (Mar 12, 2011)

I wouldn't even do it for $500.

new. for only a few hundred dollars more you can get a very decent new furnace installed and a new warranty which covers all parts for a few years and 20 or lifetime on the heat exchanger.


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## Thor73 (Oct 23, 2011)

Thanks for the feedback Doc. I forgot to mention I've had three quotes from different vendors for a new furnace:
Trane XV95 = $4000
Bryant Plus 90i 355 = $3900
Lennox - G61MPV = $5000

Thanks again for feedback.


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## Doc Holliday (Mar 12, 2011)

Thor73 said:


> Thanks for the feedback Doc. I forgot to mention I've had three quotes from different vendors for a new furnace:
> Trane XV95 = $4000
> Bryant Plus 90i 355 = $3900
> Lennox - G61MPV = $5000
> ...


 
Those are some high dollar, high efficiency variable speed condensing furnaces. I was thinking something like a simple, 80% single stage furnace. I've personallly installed those for under $1900.

You will get much more return on your invesment with a high efficieny furnace though, a lower electrical bill, better comfort, etc. etc...

It's all up to you but you have to ask yourself how long do you want to continue to patch up yesterday's failing product?

My pick of those three would be the Trane.


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## Doc Holliday (Mar 12, 2011)

One thing on condensing furances, you have a coil in the furnace. You need to absolutely make certain you replace air filters religously as well as make sure you have no air leaks anywhere, return air especially. You do not want to get that coil on the inside plugged as you pretty much have to un-install the furnace to get to it.

That and you will be needing a fresh air intake and an exhaust, both run in pvc and out of a side wall of your home.


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## REP (Jul 24, 2011)

Your problem could of course be a natural defect in materials or of manufactuer,but ususlly it is a problem of bad duct size or design or an improper size furnace.
Unless you enjoy spending big dollars on an often basis you should pay someone to do a manuel "J" ,AND a manuel"D"
If you just decide to repair what you have,you will just be at this point again in half the time you would normally have to,plus you will be paying too high a monthly fuel bill until you get the proper size and correct ductwork installed.


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## beenthere (Oct 11, 2008)

REP said:


> Your problem could of course be a natural defect in materials or of manufactuer,but ususlly it is a problem of bad duct size or design or an improper size furnace.
> Unless you enjoy spending big dollars on an often basis you should pay someone to do a manuel "J" ,AND a manuel"D"
> If you just decide to repair what you have,you will just be at this point again in half the time you would normally have to,plus you will be paying too high a monthly fuel bill until you get the proper size and correct ductwork installed.


Yep, most likely caused by a combination under sized duct and an over sized furnace.
Have a load calc done to find out what size furnace you really need. A static pressure test can be done to determine if your duct work is large enough.

What size is your house, and what is the full model number of your furnace. What size furnaces are they quoting.


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## Marty S. (Oct 31, 2009)

It's a 92% or better AFUE furnace with a lifetime heat exchanger warranty so you won't get much better buying new. The reason many cracked was of a slight burner misalignment. Lennox includes new burners,burner box and all gaskets with the exchanger so it doesn't happen again. Takes me right at 2.5 hours to replace a heat exchanger in one plus shipping cost. I'd suggest calling around and finding a company with less overhead who doesn't need to charge $500 an hour to make a profit. Same guy with a freaking $5000 G61 I'm guessing?


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## COLDIRON (Mar 15, 2009)

Replace after heat calcs are complete. Do not repair.


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## Tator1076 (Dec 22, 2009)

I just did a furnace heat exchanger on a 17 year old furnace Friday and found out the company who ever up it in. Put in 150 btu and it should be 80 btu furnace. Said part it is was 17old furnace is still under warranty but a new heat exchanger will be crack in a year. He going to have to go after other company or we put in the right size.


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## ben's plumbing (Oct 6, 2011)

I would like to know who charges 1500.00 to install heat exchanger ..by the book this spects out at 3.0 hrs .....any decent company would like to have this job at 300.00 to 400.00 including travel..keep looking around...good luck


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## gregzoll (Dec 25, 2006)

Thor73, here you go for some pricing comparisons http://www.alpinehomeair.com/viewcategory.cfm?categoryID=470 As for the heat exchanger, that is a long job for just a homeowner, and not even worth the time.


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## gregzoll (Dec 25, 2006)

Tator1076 said:


> I just did a furnace heat exchanger on a 17 year old furnace Friday and found out the company who ever up it in. Put in 150 btu and it should be 80 btu furnace. Said part it is was 17old furnace is still under warranty but a new heat exchanger will be crack in a year. He going to have to go after other company or we put in the right size.


Only way that it would crack in a year, is if there is another underlying problem causing it in the first place.


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## beenthere (Oct 11, 2008)

ben's plumbing said:


> I would like to know who charges 1500.00 to install heat exchanger ..by the book this spects out at 3.0 hrs .....any decent company would like to have this job at 300.00 to 400.00 including travel..keep looking around...good luck


400? Including travel. Heck no, thats a cheap company. Not paying their employees much.


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## Thor73 (Oct 23, 2011)

Thank you all for the feedback! To follow up on a few of the threads, no company provided a written load calc but after talking to all three, it sounds like it is oversized. My current unit is 75k BTU. The Lennox dealer did not provide any load calc information when asked and specified a 70k BTU unit. The Trane dealer talked through his hand written calculations and specified a 60k BTU unit. The Bryant dealer said his experience tells him that the unit may be oversized but he specified a 75k BTU unit. The only dealer to do a static pressure test was the Trane dealer and he indicated that the test indicated that there is a pressure differential indicating the A-coil may be dirty. 

Based on the differing feedback, I am discouraged by the quality of each company except the Trane dealer who seems better than the rest. However, I'm not sure that is a good thing.

Sounds like the most important thing to do is get the sizing right. Couple questions about sizing it correctly: 

1) Should a manual J be more official than "experience" and/or hand calcs?
2) Is there an easy "Do it yourself" J calc or free on-line calculator?
3) Does a manual D make sense to do on an existing house where I have no exposed ductwork except the 6x8 furnace room?

Thanks for the continued feedback!


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## Doc Holliday (Mar 12, 2011)

I don't know of any free programs nor do I have a link but I know these other guys know of some and have links. You can try a site search to find it as it's been posted a few times.

You have to buy the brogram and input all data.

If you really want to study up on it you can Youtube search "Heat Load Analysis" and find some excellent lectures. 

Some of are very lengthy as in an hour each and in four parts but well worth it.

These guys will be here tomorrow to post some links.


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## REP (Jul 24, 2011)

There is a $50 load calc provided on another site.Someone should have that site handy for you.
I guess I'm miss reading your answer.Are you saying that as long as you can't see bad duct sizing,you want to live with it???
A maqnuel "J" is either a hand written exersize or a computer program using paradiems set forth by HVAC engineers.It is accepted in every state requiring load calculations for almost all homes.Anything else is wild eye guess


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## Thor73 (Oct 23, 2011)

I don't necessarily want to live with poorly sized duct work but am wondering how one goes about performing a Manual D. I'm not familar with how that is done and curious if it would make any difference if the ducts cannot be seen (e.g. is a manual D only used for designing?). Is it typical practice to request a Manual D during a furnace replacement?

For the manual J, it sounds like it should be standard practice for reputable companies to provide a handwritten or computer print out of the calculations. I'll check for one of those on-line programs you mention and also call the furnace dealers to see if they can provide something in writing.

Thanks again for all the helpful feedback.


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## Doc Holliday (Mar 12, 2011)

With different sized systems, producing different cfm, you'll be NEEDING new duct work. A Manual D is related to the Manual J by way of the J sizing the sytsem for a home which produces said certain cfm and the D allotting the full capacity of cfm as a total in a breakdown to each room via the duct.

Make sense? I think I lost myself on that one! 

http://www.ahrinet.org/App_Content/ahri/files/Homeowners/manual%20D%20calculation.pdf


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## beenthere (Oct 11, 2008)

Thor73 said:


> Thank you all for the feedback! To follow up on a few of the threads, no company provided a written load calc but after talking to all three, it sounds like it is oversized. My current unit is 75k BTU. The Lennox dealer did not provide any load calc information when asked and specified a 70k BTU unit. The Trane dealer talked through his hand written calculations and specified a 60k BTU unit. The Bryant dealer said his experience tells him that the unit may be oversized but he specified a 75k BTU unit. The only dealer to do a static pressure test was the Trane dealer and he indicated that the test indicated that there is a pressure differential indicating the A-coil may be dirty.
> 
> Based on the differing feedback, I am discouraged by the quality of each company except the Trane dealer who seems better than the rest. However, I'm not sure that is a good thing.
> 
> ...


If the install manual is there for your old furnace. proper static pressure check used in conjunction with the fan data in the manual will tell you/them if your duct work is sized adequately for a new smaller furnace. Or if it is still under sized for a new smaller furnace9and how under sized it is for the current furnace.

Depending on how under sized it is, it may only need a minor alteration. Or none at all for a smaller furnace.


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## Patrick Eubanks (Oct 6, 2011)

*Hvac*

If your not changing the ductwork or the AC coil there is no need to do a manual J. You started this thread asking about a heat exchanger or a new furnace. If you want a new configuration then ask the service techs about a new system and not the cost of a new furnace vs. a heat exchanger. I would start by asking the rep. what he suggest for correcting this problem and then weigh my options from there.


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## beenthere (Oct 11, 2008)

Patrick Eubanks said:


> If your not changing the ductwork or the AC coil there is no need to do a manual J.


Sure there is. Why put a 60, or 70,000 BTU furnace in when a 40,000 may still be over sized. but the duct work is better suited to a 40,000 then a 70,000.

A 70,000 95% should have 1231 CFM to have a 50°F temp rise, while a 40,000 95% only needs 703 CFM for a 50°F temp rise.


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## Patrick Eubanks (Oct 6, 2011)

*agreed*

Agree with this except my point is that correcting the sizing of a system needs to start with the AC. Sizing a system for heat is a moot point when you are handcuffed by a certain AC coil. 740 cfm is not going to be enough for a 3-ton AC coil. The furnace should be selected for its blower capability with the minimal gas that is available. A 3-Ton blower may only have 72,000 or 90,000 BTU available. I am a strong supporter of load calcs. but also believe that if your not going to adjust the entire system to the findings, your wasting your time.
I dont disagree with your point and on a heating olny system this is absolutely true. Maybee Im assuming too much in assuming AC is installed as well. Sometimes I have a tendacy to assume too much.


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## beenthere (Oct 11, 2008)

Patrick Eubanks said:


> Agree with this except my point is that correcting the sizing of a system needs to start with the AC. Sizing a system for heat is a moot point when you are handcuffed by a certain AC coil. 740 cfm is not going to be enough for a 3-ton AC coil. The furnace should be selected for its blower capability with the minimal gas that is available. A 3-Ton blower may only have 72,000 or 90,000 BTU available. I am a strong supporter of load calcs. but also believe that if your not going to adjust the entire system to the findings, your wasting your time.
> I dont disagree with your point and on a heating olny system this is absolutely true. Maybee Im assuming too much in assuming AC is installed as well. Sometimes I have a tendacy to assume too much.


Most 40,000 BTU furnaces have a 3 ton drive. So as long as the OP's A/C, if they have it, isn't more then 3 tons, it makes no difference weather they have A/C or not.

In some areas of Texas and some other western states, its common to have a 100, or 120,000 BTU furnace in a home that only needs 60,000 BTUs of heat, but needs 5 tons of A/C. I don't believe that is the case with the OP though.


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## Patrick Eubanks (Oct 6, 2011)

*ok*

I dont think we are disagreeing on anything except the necessity of a load calc. I would select the minimal BTU available on 3-Ton blower if its a 3-ton ac. In my case, the minimum BTU available is 54,000. In severe cold climates 54,000 BTU might not get it done but Im betting the contractor instlling the unit has looked into this.


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## beenthere (Oct 11, 2008)

I find that most contractors will just put in a furnace that they are sure won't give them a call that it can't maintain set point. Even if it means its 50% larger then needed.

It will be interesting to see if the OP does a load calc and comes back and post the results. Along with weather or not they have A/C and what size it is.


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## Thor73 (Oct 23, 2011)

Some more information and and update:

- My home is in MN and I have a 3 ton AC. 

- I contacted all three companies about getting the load calcs and only one refused. Unfortunately, it is the Trane rep who had been the most helpful so far. He said he will share it if I wind up going his way. Not sure why he is holding this tight to the vest when it could lose him a job.

- Once everything comes in, I will share for comment.

Thank you for the continued feedback!


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## beenthere (Oct 11, 2008)

So contractors don't want their work(load calc) being used by other companies, so that those companies can charge less because he did all the load calc work.


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## Thor73 (Oct 23, 2011)

*Update*

Hi all -

I have some more information to run by the group for feedback.

A) I received two load calculations that are very similar and indicate a requirement of 45,739 BTU. This was then multiplied by a safety factor of 1.1 in each case to around 50,313 BTU. Both conpanies indicated that their 96% 60k BTU furnace would be the correct size.

They both checked the duct work and were satisfied with the size and quantity of delivery and return air vents. Neither said that they would do a manaul D calculation.

B) I did ask about the size of the furnace seeing that the blower compartment is 16" and my existing unit is 20" and what their plan was during installation to ensure the air flow was adequate. They responded differently:
1) build the unit up on a box so that it has a 20" opening that matches my current filter size and return air duct.
2) fit a reducer on the air filter to funnel the air into the smaller opening. They would also adjust the return air duct leading into the filter to ensure the air flow was appropriate and the static pressure was appropriate.
Any one way better than the other?

C) They offered two different thermostats. One a Braeburn 5000 and the other a Honeywell 800. Any thoughts?

D) Last but not least, the labor warranty was different. One was 2 years and the other was 5 years.

Thanks for the feedback!


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## beenthere (Oct 11, 2008)

I prefer Honeywell thermostats.

Either way for the return will work. Its which one you feel more comfortable with.


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## yuri (Nov 29, 2008)

Is there more than 1 Lennox dealer in your area? My co charges $600 -$800 to change a heat ex. If you can find someone for under $800 then it is worth repairing. Prices vary a LOT all over the country(s) depending on your local cost of living. You can also get a modulating furnace from all the major manufacturers so pinpoint sizing is not always paramount. For ex. one brand has a mod unit that fires 35 and 70 and 100%. Takes 17 mins B4 it goes to 100% so it goes there less than 10% of the season. At 70,000 BTU you do the maths for the lower 2 inputs and it is really what you need. Lot more comfortable too.


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## ben's plumbing (Oct 6, 2011)

beenthere said:


> 400? Including travel. Heck no, thats a cheap company. Not paying their employees much.


 you really can't assume anything about a company if you don't know them. only impute bad motives...... ben


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## beenthere (Oct 11, 2008)

ben's plumbing said:


> you really can't assume anything about a company if you don't know them. only impute bad motives...... ben


Guess it depends what you call getting paid much.


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## HvacWiz (Nov 24, 2006)

ben's plumbing said:


> I would like to know who charges 1500.00 to install heat exchanger ..by the book this spects out at 3.0 hrs .....any decent company would like to have this job at 300.00 to 400.00 including travel..keep looking around...good luck


 
*I agree:thumbsup:*


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