90 percent gas furnaces for packaged units

[mt31]

Why is there not a 90% gas fired heating and cooling packaged units. If there is a unit, where do I find it?

 

[boilerdoc]

What the heck does this question want to ask ???

 

[davefitz]

90% of what?

I assume you mean a 90% HHV efficiency. Most smaller units that meet the 90% HHV efficiency use pulsed combustion and partial condensing of the fluegas. 2 issues with this are (a) noise from the pulsed combustion and (b) stack corrosion and required fan head to pressurize the stack to exhaust the fluegas. For smaller units a CPVC stack might meet building codes, but for larger units it might not meet fire code, and a pressurized exhaust is a risk to occupants.