HVAC help

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Oct 8, 2011
I have an old Rheem furnace that I need to know the amount of gas pressure it needs to read at the pressure tap "Rheem Imperial Glass Lined" circa 1971 the Model number is 3404-125JD Serial number CN3D2B3 F3674 1632 125,000 BTU input 100,000 BUT output thanks
its blurred in your picture but its in the lower left hand corner of the plate...... "WC that is inches of Water Column. there are conversion tables to turn that into psi
the EXT static pressure is just the air pressure created inside by the blower running I need to know the manifold gas pressure im thinking it should be about 3.5" WC pressure but i cannot find it listed anywhere on the unit
3.5" wc is about right if you're on NG. (Propane would be around 11.5" wc or so). Make sure you're measuring that wc when ALL devices are in operation. Your gas system needs to be sized and regulator set such that is can supply the pressure (3.5" wc) when not only it is running, but also all other gas appliances simultaneously. You may need to make altitude corrections if above 3000 feet (that's a generic answer for all; it won't be an issue in the Windy City). BTW - your homemade manometer is nice. That's exactly how I did it when setting my propane regulator. No one needs an expensive tool when homemade gives you the correct answer!
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A a child of the 1980's (just barely though), they must has had a sale on green/yellow pigments in the 1970's because everything was this colour it seems. LOL
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1971 ?!?!?! I sure hope you have MULTIPLE working CO detectors in this dwelling (and that they're not older than a few years old; they do 'wear out' and old ones (pre 2009) give NO WARNING at all . . .)
I have a couple brand new carbon monoxide detectors all testing well. Where would this supposed Carbon monoxide come from? I have inspected heat exchanger already, no cracks. Also think about this, the air in the actual heat exchanger is under much lower pressure than the air outside the heat exchanger that is being compressed by the blower. With a crack or even a hole, the air is going to be pushed INT0 the heat exchanger which would cause the flame to look different or wavy. If really bad the flame would be pushed out of the front of the furnace where the gas and air enter.
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