High Efficiency PVC Vent Through Modified Furnace Vent?

I don’t see any issues out side of the sealant failing. In the report should I just write in need of monitoring? -For Mock inspections

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Read the manufacturer’s installation instructions. There will be one or more noncompliant issues.

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I would call it out as incorrect flashing. It is just a matter of time before the sealant fails.


I would steer away from “monitoring”. The entire house needs monitoring, it is part of home ownership. If you do go that route, I would be sure to mention what is to be monitored, how often it needs to monitored, what is the condition change that requires action and finally a recommendation if the condition changes.


Morning, Taylor.
You must discribe the material better.

PVC pipes are generally categorised into four: PVC-U unplasticised PVC), C-PVC (chlorinated PVC), PVC-O (molecular oriented PVC) and modified PVC .

PVC Flue in abandoned galvinized steel flue…
Schedual-40 PVC. No cap/scereen to protect from rodent emtery.
Refer review by a licensed HVAC contractor.

The question I have is; If this is a vent (exhaust/intake) from a HE furnace that terminates in a vertical run, why does it not have a “U” fitting or some sort of rain cap on it? Seems water would go down that pipe right into the system. :thinking:

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Typically the manufactures seem to specify a downturn for the intake only. I suppose the rain that gets in the exhaust will go to the condensate drain so shouldn’t be too big of a deal. But definitely important to have any horizontal sections sloped back towards the furnace.


Good point Ryan. I’m guessing the condensate line is sufficient to handle excessive rain water entering the pipe? I don’t know… :thinking:

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The furnace does not care how it terminates the roof or what is used as a chase.

Like others have said, it will be a maintenance item as ever HVAC contractor uses the cheapest Dap caulking, they can find.

I guess it isn’t as much water as one would initially think. You sent me into the deep dive and ChatGPT helped me out. A typical one inch rain event will send less than 1/4 cup of water down a 2" exhaust vent.

How much water will collect in a 2 inch diameter glass with an inch of rain?


To calculate the amount of water that will collect in a 2-inch diameter glass during an inch of rain, we need to consider the volume of water that the glass can hold.

The volume of a cylinder (which is a reasonable approximation for a glass) is given by the formula:

V = πr²h

Where: V = Volume π = Pi (approximately 3.14159) r = Radius of the glass (half the diameter) h = Height of the water column

Let’s calculate the radius of the glass first: Radius (r) = Diameter / 2 = 2 inches / 2 = 1 inch

Next, we need to convert the height of rain from inches to the same unit as the radius (in this case, inches).

Given: Height of rain (h_rain) = 1 inch

Now we can calculate the volume of water that will collect in the glass:

V = πr²h_rain = 3.14159 * (1 inch)² * 1 inch = 3.14159 * 1 square inch * 1 inch ≈ 3.14159 cubic inches

Therefore, approximately 3.14159 cubic inches of water will collect in a 2-inch diameter glass during 1 inch of rain.


Sorry to disagree Ryan, but this AI and ChatGP is going to get a lot of folks in trouble if they decide to rely on this information for their inspections. Go for it and have fun if you wish! :wink:

It’s just math. Basically, how much water (in cubic inches) is in a 2 inch cylinder if the water is 1 inch deep. And then convert the cubic inches to cups so we can easily relate to the measurement. Chat showed its work even, lol.

But does it work with the flow amount that the condensate pump can handle for that HE furnace? :thinking:

Here is the typical condensate pump found at the big box stores. Says it can pump 65 gallons per hour.

There are 4,160 quarter cups in 65 gallons. So as long as it isn’t raining more than 4,160 inches per hour, should be ok. :rofl:


So, it should be that a vertical exhaust through a roof leading back into a HE furnace should have no issues? :thinking: Why not a “U” fitting to solve future questions?

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I’m not 100% certain. I wonder if it would somehow create icing issues in cold weather climates? :man_shrugging:

The top part of a regular rubber boot might fit right over that pvc pipe if they wanted peace of mind about leaking.


Its also not painted as required.

“Monitoring” is a very poor term, in my opinion. As others have said, monitoring is part of home ownership, a task to be expected. HOWEVER, this item is on the roof. You are telling the Client to “monitor” an item normally requiring use of a ladder. CYA!!! Never tell or imply that a Client use a ladder of any type, for any purpose. Most do not know how to safely do so! Picture this comment by their lawyer - “Your honor, the inspector said my Client should monitor this. That requires a ladder. My Client fell and broke his back. We are seeking (many, many dollars) for his pain, suffering, inability to work and enjoy marital relations with his spouse”.