I have been told that my heat exchanger on my GMP125-4 furnace has 4 or more cracks by a certified technician.

This furnace is 11 years old, so I am trying to determine if I should pay to have this replaced or buy a new furnace.

How much effort would it take to replace this myself? Where might I find instructions for doing so? Where can I buy a heat exchanger on-line?

Thank you.

Get some price quotes on both,, for the repair,, and for replacement
Its no easy job,, and it depends on if you have a/c coil on furnace or not, will make a difference in labor cost,, if it was me, I`d get real serious about a new furnace

I have replaced quite a few of these myself, so that should tell you something. Even out-of-warranty, the replacement H/X isn't too expensive, but definitely not a D.I.Y. project. Factor in the overall condition of the rest of the unit, and compare unit repair cost to unit replacement cost. This job in my local market would cost between $400-$450.

It is possible you might still have a warranty from Goodman. If not buy a new unit.

To be safe you do not want to do it yourself.

It is possible you might still have a warrenty from Goodman. If not buy a new unit.
If I'm not mistaken, the GMP has a 10 year H/X warranty, the GMPN has 20.

There you have it.. If heat exchanger is under warranty, I would have it replaced by a tech. You will most likely have to pay for labor, but parts would be free. If not under warranty, I would agree that you should look seriously at furnace replacement. Hope these answers help. Let us know what the outcome is please.