I have a Goodman 92,000 Btu 4 speed single stage high efficiency furnace. It's aparently too big for this house. My house natural gas pressure is 4 inches of water ( a little low). The manifold output is supposed to be no higher than 3.5 according to the nameplate. The trouble is that, even with the CFMs set to max, at 3.5 or even 3.2 inches of water on the manifold, the temperature rise goes to about 75 degrees which is 10 degrees over max. Can I reduce the manifold pressure with the set screw on the valve with this type of furnace (it's not a draft furnace)to cut the flames back a bit?. I would like to set it at 2.25 inches w.c. which gives a temp rise of 60-65 degrees. Even at 1 inch, there is a very strong flame with no delay in lighting although I wouldn't be comfortable with this much of change. No, there are no closed vents or blockages. The CFM table says the vents are big enough to support the CFMs. There are lots of (22) registers.