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ee2009 10-30-2009 08:07 PM

Furnace 1st stage won't run
My old 80% Single stage furnace in the attic failed. Had a new American standard 95% TWO stage furnace installed. Runs on Propane. The 1st stage just pops and sputters like a train. The 2nd stage burner runs ok. Installer replaced the whole unit and we still have the same trouble. They even cut the vent stack totally off and no change. After a min on the 1st stage there is water in the vent piping. HVAC guy says it might be a problem with the Propane mixture (too much Hydrogen)??? I have other things on the same propane tank with no problems (older basement furnace, water heater, etc) although they are all single stage units. Are they on the right track??? thanks

beenthere 10-30-2009 10:01 PM

Ask them if they set up the proper CFM for first stage. Or are they just using factory settings.
If too much air is being moved. It will cause condensate in the primary heat exchanger also. And harm the furnace.
It can cause moisture to build up in the pressure switch hoses also.

You should get moisture in the vent pipe.

ee2009 10-31-2009 08:12 AM

Thanks for the reply. Do you mean CFM at the gas port like you would adjust with a jet on a carburator for a car? Sorry, I don't know anything about furnaces. They did have a 2inch intake and exhaust stack hooked up originally and thought that was the problem because the install recommends 3" pipe.

yuri 10-31-2009 09:02 AM

The unit needs to have the proper venting size, number of elbows/equivalent feet of pipe/slope as per manufacturers specs and all that info is in the install manual.Some furnaces are very specific and finicky about the venting and need to be real close to the manufacturers specs and venting diagram. Did they check the firing rate (manifold gas pressure) on low and high fire?

beenthere 10-31-2009 11:04 AM

I was talking about the air blowing through the furnace that goes to the house.
Some furnaces, can move twice as much air as what they should for heating.

ee2009 10-31-2009 12:09 PM

Thanks for the reply, I will discuss with the installers... :thumbup:

thehvacguy 10-31-2009 02:40 PM

It is to my understanding that High efficiency furnaces would naturally condensate due to the lack of heat in the venting. That's why they are manufactured with a drain hose inside the unit. Am i missing something here?

ee2009 11-02-2009 05:27 AM

thehvacguy: I believe you are correct from what I was told by my installers. The problem they think is the propane mix not being right. Asked me to call Amerigas. Too much (more then would be normal) water condensation for the 1st stage to run correctly. 2nd stage apparently works ok.

beenthere 11-02-2009 05:51 AM

Have they ever checked the manifold pressure in first stage.
Have they checked the temp rise in first stage.
Have they checked if its pulling too much combustion air(yes, its possible on a sealed unit).

Have seen the water in the fuel excuse used many times when techs don't know how to check out a furnace properly.

ee2009 11-02-2009 09:07 AM

Thanks beenthere: I'm told they checked all that and more. They have an "Expert" coming in from American Standard to check the situation. Not sure when but hopefully this week.

beenthere 11-02-2009 09:30 AM

Lets say your furnace is an 80,000 BTU 2 stage.
So in first stage, it would be firing at 52,000 BTUs.

So they are saying that a single stage 50,000 BTU furnace wouldn't work because of the moisture in the LP.

Hopefully the "expert" they're bring. Will really check everything.

SKIP4661 11-02-2009 01:07 PM

I am not sure about your furnace but most furnaces come from the factory set up for natural gas. Most have an LP conversion kit that must be installed before operating the furnace on LP. I believe 2 stage furnaces require different burner orifices and a manifold pressure adjustment. May be other things that need to be set up as well.:thumbsup:

Marty S. 11-02-2009 04:55 PM

Post up when you get the answer ee. I've seen furnaces not work right if the intallation instructions were not followed but never had water in the propane yet.

ee2009 11-02-2009 05:10 PM

Talked to my plumbing company sales rep who talked to the American Standard expert/trainer. Supposedly this is a brand new type of system they are introducing and haven't fully trained all of the installers yet. The 1st and 2nd stages apparently need to be adjusted differently from the normal way of doing gas pressure checks. I was incorrect, this is a three stage system, not two stage.

They are coming tomorrow to try again, will let you all know. Thanks for all the support...

mrairflow 11-03-2009 06:24 AM

on the 3 stage 95 furnace you adjust 1st and 3rd stage and 2nd stage is self adjusting also it is best to use the stainless steel burners with propane so they dont rust

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