Furnace venting

Just read the venting literature for the American Standard sealed combustion, haven't read it lately so I thought I better see if there is anything new.
They are now saying you can come off the top of the furnace and go to the bottom and vent out the crawl space, that is if you slope it correctly and put a trap in the lower part of the vent. Hmmmm, we already knew this, but thanks A.S, been doing it for years.
You can now get the fresh air from the attic, Hmmm, Done it but don't like to. There is a possibility of a leaking gas valve, and if the attic is hotter than outside the make up air pipe in the attic could act like a chimney and cause the gas to go into the attic. Realistically however, that would have to be a BIG leak!
You DO NOT have to get the fresh air from the same side of the house. I wonder if that only applies to the variable speed vent furnace or all of them?
On the subject of venting, we installed a new power vented H2O tank which had a few nuisance calls. Of course the factory was of no help. Mark found that our venting was too short and the flame was lifting off the sensor due to the air rushing into the chamber because of suck a great suction from the ventilator. He put an orifice in the exhaust and adjusted the inch's of water over fire. Works perfect now.
For those who don't know it, an 80 and 90% furnace is orificed in some manner to control the negative pressure over fire, not much different than an old 60% with a barometric really. If you installed a condensing coil in a 70% furnace and you can make it close to a 90% with consistent control of pressure over the fire box. Had a lot of problems with YORK back in the late 70's/ early 80's. Tore the things apart and under the combustion vent motor was a plate, you would use the proper plate according to your fuel. Had problems with flame roll out, since I couldn't increase the secondary air I increase the negative pressure over fire by increasing the orifice size on the plate between the vent blower and exchanger. There was some efficiency loss but never had the problem again. Two buildings over a YORK truck was working on a unit and we spoke with him, he was having the same problem. Mark and I kept our mouths shut........ they make the big bucks, let them figure it out!
Just thought I'd pass on this info, I'm kind of laid back tonight wondering which customer will cut my jewels off this week because we can't get to them immediately. :-) Rich
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The biggest issue I see here is pulling in dirty air. Especially, if someone has been up there with blown-in insulation. Or for heaven forbid, add addition blown-in insulation!!!!!

ICP still requires it to be in the same atmospheric area.
"This furnace uses outside air for combustion ONLY, it MUST be taken from the
same atmospheric pressure zone as the vent pipe."

Bradford White? If so, they discuss this in there installation manual.

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That answers my question if this was just for the Variable speed vent blower furnace that Trane/American Standard makes.
Thanks
Rich

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