If the exhaust pipe goes through an unheated space it will have to be insulated. You can cover it with a armaflex insulation or box it in and insulate it.

There are many varying opinions on Goodman equipment. Do a search on "Goodman problems" on this forum and read what people have said.

There are also differences of opinions about Lennox. The cheap stuff made in Mexico should be avoided.

Tell the Lennox contractor he should read the installation manuals before recommending you replace your hot water heater. Is there anything wrong with the current dampers and zoning panel that require them to be replaced? If you are getting a 2-stage furnace then you should get a true 2-stage thermostat.

I suggest you bring in more contractors.

>I've read a lot of stuff about Goodman, not all good - but it does appear that if properly installed, it can be a good unit?

Yes. If any contractor bashes a brand, ask them for a specific technical explanation of why that brand's products are inferior to the rest. If they can't come up with a direct answer to that question, kick them out of your house. I have worked with both, and can't come up with such an explanation for either Goodman or Lennox, so I refrain from saying their products are worse than the competition. They all use the same basic design and for the most part, the same components.

Instead of avoiding a particular brand, I would advise that you avoid the low-end stuff of any brand. The Lennox SLP98V and Goodman's 96% 2 stage are certainly not low end.

Your Rheem 100K is probably oversized, make sure the contractor you select does a Manual J load calculation to figure out the correct size. If they just put in a new 100K furnace, especially a high efficiency one, it will be even more oversized.

You should definitely go with a 2 stage or modulating furnace in that climate. Normally in MA a 2 stage condenser would be overkill, but it might be worth it since you're zoning. If you get the SLP98V I would want the Harmony III zone panel to properly control the modulation and the variable speed fan for zoning.

Sorry, forgot to mention that the Lennox being proposed is 90K BTU while the Goodman is 80K BTU.

If we do end up going with the Goodman 2 stage, what thermostats do you recommend?