Condensing furnace sharing flue pipe


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Old 01-19-19, 07:17 PM
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Condensing furnace sharing flue pipe

I was at my friends house and found this.

It is a big house with 2 water heaters and 2 furnace.
2 water heaters are natural draft connected to a flue pipe with B-vent and 2 furnaces are condensing furnaces and connected to B-vent flue using PVC pipe. One with 3" and the other one with 2"

From what I know, condensing furnaces are supposed to be vented outside individually and that is all I have seen before.


There were condensation water dripping to the floor from bottom of B-vent flue as well.
 
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Old 01-19-19, 07:25 PM
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I'm not an expert on condensing gas furnace venting but the PVC lines are supposed to go directly outside. As far as I know they cannot dump into a flue like that. There'll be condensate all over the flue. I have seen them go up thru the roof but never in a common flue like that.
 
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Old 01-20-19, 08:43 AM
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That is what I thought.
Guess have to read manufactuer's installation manual for 100% proof.
 
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Old 01-20-19, 09:12 AM
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How often do the carbon monoxide detectors go off?
 
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Old 01-20-19, 09:14 AM
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That’s extremely dangerous and against code.
The condensation within the flue gas rots out the B vent quickly. Leading to flue gas leaking into the space.
Individual PVC venting MUST be run all the way to the vent termination outdoors.
The way they have done it there, the bottom B vent is likely full of acidic condensation up to the PVC.
 
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Old 01-20-19, 03:02 PM
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How often do the carbon monoxide detectors go off?
I don't think they have one.
No one died from carbon monoxide poisoning, so I guess it isn't leaking too bad yet.

The owner is trying to sell this house and he doesn't live in this house. I doubt if he will fix this unless home inspector points out when he sells the house.
 
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Old 01-20-19, 04:44 PM
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Most over the counter CO detectors from big box stores are really worthless and shouldn’t be trusted.
They are purposely set not to go off until ~70 PPM, to avoid nuisance trips. The trouble is brain damage, unconscious or nausea may have already set in by the time they alarm.
Low level CO detectors are what you’d want.
Hopefully the home inspector finds it and flags the furnaces.
 
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Old 01-21-19, 02:36 PM
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Found manual right next to the furnace and it confirms that it needs to be vented directly outside.

Also found additional problem. There were 2" to 3" transition on horizontal section, which I though will collect condensation.
And the manual actually says not to do so.

LOL

On a bright side, the furnace room is right next to outside wall of a half basement.
The problem is it is concrete wall (cause it is in basement) and also has red brick wall outside.
Will need a core drill even if we go through joist header.
 
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