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12-16-2011, 09:09 AM #1
hvaceric doing training on combustion analysis. We took a Heil 80 that we removed from a home. The competition said it had cracks but the HX was sound as can be. We hooked it up to our gas line and vented in 5" single wall to the 4" b-vent for our tube heater.
Picture 2 shows the 5" flue about 80% blocked. Did it bother the pressure switch?
Picture 3 says no. Pressure switch opens at .65" WC while the manometer says .81 so despite the horribly blocked flue, furnace kept purring along.
Picture 4 shows the draft gauge after the block. Very strong draft. Between the inducer and the block, the flue went positive meaning exhaust could come out any joints in the pipe. CO production went up with this blockage too.
Picture 5 shows a hole Eric drilled in the HX. It affected nothing. CA readings stayed the same as did draft. We had the burner door on top of the outlet providing some static pressure.
12-16-2011, 11:56 AM #2
That is education at its funnest. I would have liked to been there. I wonder what the tolerance of those switches is new? We also see many of these pressure switches that are out of spec in the field. Is it cheap manufacturing, or self-limiting caused by the application?
Thank you for sharing.
12-16-2011, 01:29 PM #3
The PS in the furnace tended to drop out at .7" so slightly quicker than the .65 rating.
12-16-2011, 09:52 PM #4
very good info! hopefully the vent switch works.just goes to show why CA is so important
12-16-2011, 09:53 PM #5
i used to breeze thru gas furnace PM's. Now that i am more educated and have more tools to do the job correctly it takes me about 45-60 mins on a PM
12-16-2011, 10:01 PM #6
Great hands on training!
12-17-2011, 01:25 PM #7
Just common vent this 80%'er to a natural draft water heater with a draft hood. That way, when the flue is blocked it can vent out of the draft hood and not shutdown the furnace.
I hope ya'll realize I'm being facetious here but it makes a point:
when you common vent an 80% furnace with a water heater, you bypass three primary safety controls on the furnace to a water heater that has NONE-pressure switch, flame rollout and high limit.
Great training by The Bald One! I hope ya'll see the value of in-house training in addition to formal outside training by agencies. Now, keeping Loonie's point in mind, do YOU test safety controls and compare to spec?
Now, if you have a WH common vented, how do you propose to protect the occupants?
12-17-2011, 04:50 PM #8
Gotta give this credit to hvaceric. He's got all the tools and taken lots of training.
12-17-2011, 11:56 PM #9
What was the rating printed on the pressure switch? Sounds to me the pressure switch was bad.
The rating on the pressure switch is the pressure at which the switch makes. It should break .15 above that rating. So if the rating was .65 than .8 is where it should have opened.
12-18-2011, 07:20 AM #10
Lot of guys will condemn a HX after they put on a new PS and or inducer and it still doesn't work.Contractor locator map
How many times must one fix something before it is fixed?