That particular Goodman furnace vents with 2" pvc, but it is still not allowed to be in the chimney space with another vent.
Aside from the venting, the GMV furnace is a great little furnace. Variable speed blower capable of fantastic dehumidification during cooling and thermostatically controlled two stage furnace make it great on features. The lifetime heat exchanger warranty with 10 year unit replacement ain't bad either. I am not familiar with the Coleman, so cannot state which is best.
I'll take your word for it, but like everyone says, equipment is only as good as the installer, and even though people say Goodman has gotten better, they still have installers who aren't that bright.
Silly me, I know nothing about venting water heaters or furnaces and I had no idea that they would vent a water heater through a chimney.
I have good references for both companies but I'm leaning towards the one selling the Goodman because I don't really want a bunch of steam coming out the side of my house. I will get a little more information from them on exactly how they will be venting the furnace before I accept their bid.
I have 2 furnaces in my house.The main structure has a Carrier that was installed about 20 yrs. ago.The addition has a Coleman that I installed 10-12 yrs. ago.Since then the Carrier has had the ifc replaced, and the Coleman has had the hot surface igniter replaced.Other than a dirty flame sensor that is all that I had go wrong with the either one.I live where a lot of mobile and modular homes are mfg. so there are a lot of coleman furnaces around here.As has been stated, I would get some other estimates anyway
I am not bashing either brand, both brands will work fine, there is the warranty difference and the most important issues is the installation. Ask both Companies for pictures and or maybe you can visit sites that show their work. I would go with the best installer's, shoddy workmanship would not get my work. Even as a one man shop, I have before and after pictures of my work and some pic's of the "other guy's" work, most of the time the pic's are all I need to get the job.