Armstrong SX90 Venting Question

[djlandkpl]

Need some help. The exhaust vent for my SX90 was relocated and extended due to a remodel. The HVAC contractor used 2" PVC for the entire run and now the pressure switch is kicking off the burners. I'm pretty sure it is due to condensation build up at the end of the exhaust run. After the inducer shuts off and about 20 seconds, there's a rush of condensate at the furnace drain.
The current piping is this:

Furnace >
3.5 feet vertical >
90 degree >
2 feet horizontal >
90 degree >
6 feet horizontal > this piece extends from the basement to an unheated garage
90 degree >
6 feet vertical >
90 degree >
11 feet horizontal to a 90 degree termination

Everything is pitched back towards the furnace. My hunch is condensate is building up at the end of the 11 foot run and can't fight the inducer blower pressure.

Does anyone have the exhaust specs for this furnace? I don't have the installation manual and the HVAC contractor does not handle Armstrong.

[hvaclover]

The venting pipe size is not sufficent for length.

Got way too many elbows. Venting going thru unconditioned spaces, i.e. your garage, must be insulated.

I won't get anymore specific than that. You must get a pro who handles Armstrong to advise you further.

Just curious, who extended the exhaust for you?

Are one or two pipes coming off your furnace?

[djlandkpl]

The exhaust was extended by the HVAC contractor the General contractor that built my addition uses. He's trying to make it right but just doesn't have access to the specifications for my furnace. He's going to try insulating the exhaust vent today.

There's one pipe coming off the furnace. It gets combustion air from the basement. There's a open grate on top of the burner area.

[hvaclover]

If this contractor does not have access to specs than why are you letting him insulate the pipe?

Have him contact Armstrong to get the right info to correct your problem. If he can't or won't then dump him and call somebody who will.

A knowledgeable contractor knows where, or how, to find the info he needs.

I am not joshin' when I say you have a potentially dangerous situation on your hands.

[djlandkpl]

I haven't been able to find a telephone number for Armstrong anywhere and I suppose they don't want homeowners calling for help.

Should my HVAC contractor have a method for getting the phone number for Armstrong? He's a York dealer. I don't want to throw him out yet as he is willing to correct the problem. He wants to insulate the pipe to see if it reduces the volume of condensation. In the absence of specs, he's changing parts.

[t527ed]

go to http://www.armstrongair.com use dealer locator to find dealer in your area.

[hvaclover]

I'm sorry, but I have given what you need to get on track.

I don't sell Armstrong either, but I knew where to look. In this information age I find it difficult to believe someone in our industry can't locate info with all the resources available to them.

[BaldLoonie]

Hello Brucie, need the venting tables for the old SX90s. Thanks.

Fax machine rings, here they are!

Of course without knowing what furnace, makes it hard to help out here

for the 50K furnace, with 4 ells you can have up to 20' of pipe

for the 75K furnace, same

for the 100K furnace, 5' of pipe

for the 125K furnace, no 2" allowed

So undersized vent, should be redone in 2.5" or 3"

[djlandkpl]

BaldLoonie, thanks for the help.

I have a 100,000 BTU furnace. Are you saying there can be no more than 5 feet of 2" pipe?

[BaldLoonie]

That's what the chart said! Less elbows would allow a few more feet but not many. You were likely at the max before it was changed.

[hvaclover]

Sounded like he was fishing to me.

[4l530]

[djlandkpl]

The saga continues...
The exhaust piping was changed out today to 3 inch. The portion that is in the garage is also insulated. When the tech fired up the furnace after changing the pipe, the burners ran for about 5 minutes and then shut down. After about 30 seconds, the ignition sequence started over again and the burners continued to run. The tech jumped the pressure switch and the burners shut down again. On the next shut down he checked the voltage coming from the MV and PV jacks on the module and both read 0. The module is a Honeywell S8660K. Tonight the furnace ran through 3 cycles without the burners shutting down. The tech is pretty sure it needs to be replaced but his boss has to get me pricing. Since the problem is intermittent, could it be a bad module? Will modules slowly fail or do they completely stop working when they go bad?