I have a small shop and I have a chance to purchase a used furnace (Goodman model GMPNO 80-4) I would like to know if this would be good > The shop is a woodworking shop of about 900sq.ft. and I want to know if this can be installed in a horizional position in the overhead craw space and also if it is compatible for future addition of an AC coil. I am a master electrician not an hvac tech but I am going to try to install the unit myself . Advice please . Thank you ,cowtowndude

Check the primary heat exchanger for leaks, as these units have a very high failure rate. Look over the primary cells for missing/broken stamp rivet ring heads. Remove the draft inducer and examine the plastic (yes, plastic) flue collector for cracks. I hope you are getting a good (free) deal on this unit, as you may spend in repair dollars what you saved going with a used Goodman.

As KC said, unless you are getting it for free, it may not be worth it. Look around online for new equipment that will come with a warranty.