With AC Running, Humid Outside Air Drawn Into Combustion Chamber Is Condensing

[Mark Lyons]

I have a gas furnace in my house that was installed in December of 2014. Several days ago the circuit breaker for this unit tripped. In resetting the breaker the unit failed to respond. I decided to investigate by removing the combustion chamber panel only to find a puddle of water on the floor of the chamber. And sitting right in this puddle is a safety interlock switch (normally open) which shuts down the system if the panel on the blower compartment is removed.

I removed the blower panel then manually worked the switch's spring loaded plunger several times. There was a sizzling sound inside the switch and a wisp of smoke arose from it. This was obviously the cause of the breaker tripping but the more disturbing issue was the water that was emanating from the 2" PVC intake air pipe that enter the combustion chamber from above. This is the same pipe that brings outside air into the furnace when the unit is set for heating.

Every metal component directly below the entry of this PVC intake pipe is corroded; parts of the burners, the burner valve, and the steel gas pipe feeding the valve. There is water on the same components as well as electrical connectors on the wiring harness. Then there is that interlock switch mentioned earlier.

Since the unit is still under warranty, I called and left a voicemail message with the local HVAC contractor who installed the unit. I described the exact condition outlined above and asked why some sort of condensate trap had not been installed on the intake air pipe.

Later that afternoon the owner called me and told me that this has become a common problem with my type of unit. He went on to explain that it only occurs during hot humid weather in this part of the county (we are in Southern New Jersey). Then went onto say that the manufacturer (York) is reluctant to recognize this problem and thus has not offered a solution. He will be calling to schedule an appointment to try and remedy my problem this week. He said that he can install some sort of "gutter" device on the intake pipe to intercept the condensate collecting along inside wall of the pipe.

Has anyone else out there experienced this problem? IMO this is a disgrace that a big name manufacturer like York has overlooked the eventuality of this happening. I payed $4500 for this unit to have this happen. My last furnace was a Trane and I got 18 years out of it until the heat exchanger ended up with a possible breach in it. I hope that someone initiates a class action lawsuit against York. If I could get my money back on this piece of garbage, I'd have it removed and a Trane furnace installed.

 

[Stuff]

To get condensation you would need a lot of air being sucked through the pipe as well as the pipe being cooled down (in front of an a/c register). This normally can't happen as long as both intake and exhaust are routed to the same location outside.

What does the outside look like? Normally issue is with pipe pointed up or horizontal that gets rainwater coming in.

What is the model # of the furnace? That grey hose doesn't look normal but might be depending on model.

 

[Sponsor]

 

[Dana]

In NJ in summer the outdoor dew points are higher than basement temperatures, but it still takes quite a bit of air flow for this to be a true condensation issue.

Normally with condensing furnaces and boilers the exhaust plumbing and air intake plumbing terminations are at roughly the same elevation,which prevents convection through the unit when it's not running. How much elevation difference is there between the intake and exhaust terminations outside the house?

There is usually a condensate trap on the exhaust piping to manage exhaust condensation, and a similar trap COULD be installed on the intake side, but without a better understanding of what the real problem is that might not really take care of it.

I've never seen this movie- can't tell you for sure how it ends.

 

[Mark Lyons]

To get condensation you would need a lot of air being sucked through the pipe as well as the pipe being cooled down (in front of an a/c register). This normally can't happen as long as both intake and exhaust are routed to the same location outside.

What does the outside look like? Normally issue is with pipe pointed up or horizontal that gets rainwater coming in.

What is the model # of the furnace? That grey hose doesn't look normal but might be depending on model.

.

Both the intake and the exhaust are routed to the same location outside.
The pipe terminations outside are as follows:
Intake come out horizontal then takes one 90 degree turn down.
Exhaust comes out takes a 90 degree turn up then another 90 degree out.
The furnace is a York model TM9E
I agree, I have no idea what the function of that grey hose is.

 

[Mark Lyons]

In NJ in summer the outdoor dew points are higher than basement temperatures, but it still takes quite a bit of air flow for this to be a true condensation issue.

Normally with condensing furnaces and boilers the exhaust plumbing and air intake plumbing terminations are at roughly the same elevation,which prevents convection through the unit when it's not running. How much elevation difference is there between the intake and exhaust terminations outside the house?

There is usually a condensate trap on the exhaust piping to manage exhaust condensation, and a similar trap COULD be installed on the intake side, but without a better understanding of what the real problem is that might not really take care of it.

I've never seen this movie- can't tell you for sure how it ends.

The two plumbing terminations are at the same elevation where they penetrate the building wall. Then the intake take a turn down 90 degrees and the exhaust takes a 90 degree turn up then another 90 degrees out. The vertical distance between the two openings is about a foot.

 

[Mark Lyons]

Here's an update on my situation. Last night I removed and left the cover off of the combustion compartment and there has been no further condensation trickling down out of the intake pipe. While this appears to have fixed the problem I realize that come winter when I turn the heat back on I need to replace that cover. Next I am also going to do an experiment by covering the intake pipe outside of the building with the combustion compartment cover back on and see what happens. I will update the results.

 

[Stuff]

So pipes sound normal. I wonder if the inducer is cycling when it shouldn't? Maybe that is the issue York needs to address. So could also try disconnecting wires feeding inducer motor.

 

[Mark Lyons]

So pipes sound normal. I wonder if the inducer is cycling when it shouldn't? Maybe that is the issue York needs to address. So could also try disconnecting wires feeding inducer motor.

Update on the condensation problem!
While I view this as a temporary fix, I have since come up with a remedy. On the outside of my house, I capped off the 2" PVC pipes (intake and exhaust) at their terminations. The caps can be easily removed in late fall when I switch to heat. Since installing these two caps, this there has been no further ingress of moisture in the combustion compartment. I've replaced the furnace access panel and its as dry as a bone inside. I still need to have the installing contractor come in and replace the water damaged combustion components, More on this in the furture. It's pretty maddening when a non-professional (HVAC) homeowner (me) has to waste what precious little free time I have outside of work putting band-aids on the latest HVAC technology that should have been designed correctly.