The original post, in it's entirety: "New Grandaire furnace, gas high efficiency 40k btu in 1200 sft house near boston. All new insulated duct work, hooked up and seems to run right, but the air coming out of the supplies is only about 75 degrees. Any ideas why its so cool"
Also: "73 degrees is furthest away 82 for one that is right off the plenum., "
But you are right, he's also complaining about how long it takes to heat up the house: "It was about 60 inside. Took 90 minutes to raise the temp to 68 and thats with an outside temp of 55. I cant imagine this will be any better this February."
Now the fact that the copper pipe was stolen out from the house suggests the house may have been vacant and somewhat derelict as well, which means it COULD well be uninsulated and drafty - basically an old barn - in which case the furnace WOULD be too small, but in which case it would also be much more cost efficient to seal up and insulate the old barn, rather than throw a bigger furnace at it.