I am no expert in this area.
A builder is offering me to either go for the standard "Double Vented 92% efficiency furnace sealed combustion with 2 speed blower fan" or upgrade to a "High Efficiency 2 stage furnace with ECM motor".
Can anyone help explain this terminology. The sales person was not very clear about the differences or benfits of upgrading.

Double vented - combustion air from outside and exhaust from cumbustion to the outside

Two speed - just that. Usually a higher speed for cooling and a lower one for heating. Typical

92% - It's 92% efficient of converting the BTU's in gas to usuable heat

2 stage - Usually means two burners and may also mean different fan speeds for heating. Much quieter. The smaller burner is usually a little more efficient. Especially good if climate is moderate. The high burner kicks in for a number of reasons.

ECM - Buzzword for Electronically Commutated Motor. Allows variable speeds. A little more complex. It's basically a 3 phase motor driven by an electronic circuit from a single phase supply.

Going to a two-stage system depends a lot on climate.

Dual fuel or Hybrid heat is yet another system where a heat pump is combined with gas heat. The heat pump is used when the outside temp is above a certain value.

Also do a search on ERV/HRV

Electronic Air cleaners from Honeywell or Aprilaire can also be considered. The Aprilair 5000 isn't bad, but Honeywell supposedly is a bit better. Allergies/pets/odor/bacteria The 5000 filters are about $30 and last about 6 months. They are huge. Guess about 10" wide and have large pleats.

UV lamps to kill bacteria is another option. Expensive to maintain. Good when humidifiers are used.

The operating costs between these two system are not that much different, but the two stage/VS blow could provide greater comfort as it will run more frequently (at a lower cost). Ask for some operating cost differences, and what if any changes must be made to the duct work.