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Lessons Learned from the simple Tee

JUGHNE Member Posts: 11,102
I changed out an old standing pilot furnace for a 95% 2 stage variable speed blower.
Have had numerous nuisance call backs on Pressure switch open code flashing.
Reset power and furnace would fire OK.
Inducer would show -1.1 WC and still fire.
Finally called factory tech support, they said too much restriction in piping.
I am right at the max by length and fittings.
They suggested turning the Tee at the exit of furnace so to flow thru the run rather than into the branch with the bull head effect. I had been told this at training school but never had a problem with other installs run out to max length/fittings.

So after changing I went from -1.01 wc to -1.30 wc. This really surprised me as I did not expect this much gain.
This was the pressure fitting design tee that comes with the furnace. So now have a DWV Tee with DWV street 90.
The only fitting gain was going from a non radius 90 (Tee) to a DWV (long radius) 90.
But I thing a lot was gained by having some approach pipe (about 7") between the fan discharge and the first 90.
Just general info and recommending laying that Tee down if your piping lengths gets stretched out.