Question? Minimum burner gas pressure on a Dukane 70K 92% gas furnace

[billroy]

I have a 2 year old Dukane 70,000BTU 92% gas furnace at home, it is slightly oversized, 63Deg Temp rise with 3.5" Hg gas pressure to manifold which is OK, it works great but my question is how can I de-rate this furnace a little to keep it running longer. My thought was maybe drop to say 3" HG gas pressure to manifold or lower but would that alone cause any other problems? I've been in the business long enough (but not residential) to accept if its working properly Leave it be!

[hvacrmedic]

The gas input rate is fairly critical for normal operation. Multi-stage furnaces are designed to compensate both the combustion airflow and indoor airflow in low fire to maintain normal heat exchanger temperatures and efficient combustion. Single stage furnaces don't have that capability.

[heaterman]

You run the risk of poor combustion, lower efficiency and reduced equipment life expectancy. If you are capable of doing proper combustion analysis, fine. If not, leave well enough alone. You could work toward reducing temp rise by increasing duct efficiency.