Condensation/water in furnace air intake PVC pipe

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Eric H

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Hello all,
Wanted to see if anyone has dealt with resolving condensation forming inside the air intake PVC pipe and dripping down into my furnace and on the components. It only happens when the A/C is running. Unfortunately my HVAC guy hasn’t seen this before. I also noticed a little bit of water coming out of one of the air intake connections. Unsure how to resolve this and a little worried about The furnace wires and components getting wet.
Thanks
 

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WorthFlorida

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Obviously the AC is on usually because the humidity is high. That area is getting too cold and its below the dew point of the air. Maybe not much you can do with outside air being sucked in but you can put in a drip pan. The space looks like a weber grill aluminum pan would fit. Just allow the condensation to accumulate and when the AC is not used it should evaporate. If the amount of condensate overflows the pan, add a condensate pump and fashion a nylon hose to the pan. Bring the hose to the condensate pump, usually it would sit on the floor next to the unit. The condensate pump could pump into the existing AC condensate drain. Just google nylon fittings. Most have a threaded end and the other end a barb.

Screen Shot 2021-07-06 at 4.05.57 PM.jpg
When the AC is on, the fan is causing a negative pressure in the space (I assume the basement) thereby pulling in outside hot humid air.
 

Eric H

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Obviously the AC is on usually because the humidity is high. That area is getting too cold and its below the dew point of the air. Maybe not much you can do with outside air being sucked in but you can put in a drip pan. The space looks like a weber grill aluminum pan would fit. Just allow the condensation to accumulate and when the AC is not used it should evaporate. If the amount of condensate overflows the pan, add a condensate pump and fashion a nylon hose to the pan. Bring the hose to the condensate pump, usually it would sit on the floor next to the unit. The condensate pump could pump into the existing AC condensate drain. Just google nylon fittings. Most have a threaded end and the other end a barb.

View attachment 74991
When the AC is on, the fan is causing a negative pressure in the space (I assume the basement) thereby pulling in outside hot humid air.

Thanks for the recommendation. Just to clarify, the water is going inside the furnace onto the components. Not much space in there to capture the water before it hits the gas line or wires. There are also wires running directly adjacent to the filter at the top where the pvc pipe comes in.
 

Fitter30

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Furnace in your basement? Is air leaking out of the plenum? Duct sweating or just the flue? Wally world sells a temperature/ humidity for under $20 or amazon in hardware to put in basement. With this reading can find out what due point is.
 

Eric H

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Furnace in your basement? Is air leaking out of the plenum? Duct sweating or just the flue? Wally world sells a temperature/ humidity for under $20 or amazon in hardware to put in basement. With this reading can find out what due point is.

furnace is located in the basement. My system isnt sealed completely or great so yes some air leakage is happening and it is a bit colder around the whole HVAC system of course. I see no sweating on the ducts. Only sweating or condensation on the inside of the air intake PVC pipe. Have seen some water leaking at a joint too. Concerned about the same issue in exhaust pvc pipe but obviously can’t see in there.
 

Fitter30

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Do this test turn furnace fan to the on position at thermostat. Does the basement door pull shut barely cracked or with a match see which way the air flows at the crack. Pulls to basement unit is starved for return air and is pulling air down the flue and the plate/ sill board that touches the foundation.
 

Eric H

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Obviously the AC is on usually because the humidity is high. That area is getting too cold and its below the dew point of the air. Maybe not much you can do with outside air being sucked in but you can put in a drip pan. The space looks like a weber grill aluminum pan would fit. Just allow the condensation to accumulate and when the AC is not used it should evaporate. If the amount of condensate overflows the pan, add a condensate pump and fashion a nylon hose to the pan. Bring the hose to the condensate pump, usually it would sit on the floor next to the unit. The condensate pump could pump into the existing AC condensate drain. Just google nylon fittings. Most have a threaded end and the other end a barb.

View attachment 74991
When the AC is on, the fan is causing a negative pressure in the space (I assume the basement) thereby pulling in outside hot humid air.
Also,
What’s your opinion on capping off the air intake pvc opening outside my house for the cooling season and then removing the cap before turning on the furnace? This should present humid air from getting pulled into the pipe right?
 

Eric H

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Do this test turn furnace fan to the on position at thermostat. Does the basement door pull shut barely cracked or with a match see which way the air flows at the crack. Pulls to basement unit is starved for return air and is pulling air down the flue and the plate/ sill board that touches the foundation.
If the system is starving for air, what’s the solution? Could I cap the air Intake PVC pipe on the outside of my house for cooling season and then obviously remove it before turning on furnace?
 

WorthFlorida

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It is sounding like the basement air pressure is being reduced when the fan turns on as Fitter30 suggest. The air gets pulled in from the fresh air supply for the furnace. HVAC cabinets are not the most airtight fixtures so when air is getting pulled through, air will get pulled in from anywhere.

One suggestion is add a register that can be closed off and place it somewhere past the coil to allow conditioned air into the basement. A 4x10" grill may all it be needed. This should help to balance the air pressure in the basement and not pull air in from the fresh air supply. During th ewinter you can close off the register.

whites-everbilt-registers-grilles-e102m-10x06-64_100.jpg
 

Eric H

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Tape off the intake but need to know what temp and humidity is in the basement.
I’ll try and get some readings this week. Are you thinking we might need a dehumidifier in the basement, would that help. I took a piece of paper and held it against the air intake pvc opening outside my house and it does slightly suck into the opening. It’s not a strong suction but present. It’s only there when the AC fan is on. Is it safe to cap off the intake pipe on outside with the system obviously pulling air in from the outside. I don’t want to damage anything. Also theoretically, would the system make up for the lack of air by sucking air into the separate exhaust pipe? I don’t want water condensation building up in the exhauste pipe
 

Eric H

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It is sounding like the basement air pressure is being reduced when the fan turns on as Fitter30 suggest. The air gets pulled in from the fresh air supply for the furnace. HVAC cabinets are not the most airtight fixtures so when air is getting pulled through, air will get pulled in from anywhere.

One suggestion is add a register that can be closed off and place it somewhere past the coil to allow conditioned air into the basement. A 4x10" grill may all it be needed. This should help to balance the air pressure in the basement and not pull air in from the fresh air supply. During th ewinter you can close off the register.

whites-everbilt-registers-grilles-e102m-10x06-64_100.jpg
Thanks for the input. I did place a piece of paper near the opening of the air intake pvc pipe outside and there is slight suction when the AC is on. Should I have someone check how sealed my furnace box is? I read some blogs that stated that the AC fan should not be pulling air as in the winter it’s possible furnace fumes can get out. How close to the coil would you recommend. Now that you mention this, I have a register in the basement that’s about 15-20 feet away from the AC unit thru a door that I tend to close (I close the vent, not the door) in the summer. We have a split level house with 4 levels. Our bedrooms upstairs get hot and the basement stays cool so I tend to close the vent in the basement with the theory that that air will go further along the line. I’ll open that vent up and see if it helps. My HVAC guy told me cap the intake pipe on the outside which I did today but noticed air still being sucked in thru the exhaust pipe. Obviously this will cause condensation in exhaust line. Is this safe?
 
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