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Discussion Starter · #1 ·
Hello: habe a standard atmosphere water heater (gas) venting into this square brick chimney stack going all the way to the roof from basement. Connection: 4” round double wall duct. Had a furnace replaced with HE.

can I vent into this chimney a 4”duct connected to a bathroom exhaust? I see s remote possibility of a potential backdraft if chimney opening on the top getting clogged and to counter it can and will install a backdraft damper (2 of them) at the start and end of the bathroom vent.

I can’t seem to find a good reason why this would not work.Probably codes in US (I am in NJ) will say no and to which i am not surprised
 

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Absolutely not.
And to add to that, if the company put a condensing furnace in and didn’t address the orphaned water heater, you very well may already have draft issues.
Draft issues on orphaned water heaters are so common they have received that term to describe them.
 

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Hello: habe a standard atmosphere water heater (gas) venting into this square brick chimney stack going all the way to the roof from basement. Connection: 4” round double wall duct. Had a furnace replaced with HE.

can I vent into this chimney a 4”duct connected to a bathroom exhaust? I see s remote possibility of a potential backdraft if chimney opening on the top getting clogged and to counter it can and will install a backdraft damper (2 of them) at the start and end of the bathroom vent.

I can’t seem to find a good reason why this would not work.Probably codes in US (I am in NJ) will say no and to which i am not surprised
It's a bad idea, beyond the fact that it's illegal. The fan will create positive pressure in the chimney and blow back the exhaust from the water heater, and cause CO poisoning, etc.
Also humidity from the bathroom fan will degrade the masonry to the point of collapse.
 

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Discussion Starter · #4 ·
The fan will create positive pressure and blow back the exhaust from the water heater. Well when the old 80% furnace was connected wasn't that the case too? Sorry confused.

Its a 12-in by 24-in chimney stack going from basement into 1st, then 2nd, then attic and finally almost 2-ft. A 50 CFM bathroom fan will cause so much damage due to humidity that this chimney will colapse? The hot air from water heater won't evaporate any of the water vapor? Again what am I missing here?

"And to add to that, if the company put a condensing furnace in and didn’t address the orphaned water heater, you very well may already have draft issues.
Draft issues on orphaned water heaters are so common they have received that term to describe them"
Sorry I don't understand. The company came and completely closed the hole which existed servicing the 80% with an end cap, special fire-proof industrial caulking, etc. The inspector actually commented on job well done. Not sure what you mean by orphaned water heater here.
 

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So you had a water heater and furnace vented into the chimney, the furnace was removed and replaced with a condensing furnace vented with PVC, and the water heater was left alone (orphaned) on the chimney.
Is this about right?
The flue is likely too big for the water heater alone. And can cause backdrafting. Usually when a furnace is removed from a still functional chimney, a new smaller liner is put in to accommodate the appliance left alone still using it.
As far as the bath fan, that’s not even a remote option. Backdraft dampers or not. So you will not be doing that. The moisture and products of combustion make a corrosive environment and will destroy what’s left of a masonry chimney.
 

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There's positive pressure venting and negative pressure venting. They don't mix. Your water heater uses negative pressure (natural draft from the chimney), to remove the exhaust, and your bath fan uses positive pressure to push air out of the bathroom.

I assume the 80% furnace was also a natural draft type if it was sharing a flue with the water heater. If the furnace had a draft inducer, then it would make a positive pressure venting, which would cause the same problem as the bath fan. and would therefore not have been a proper installation.

The hot air from the water heater will not eliminate humidity from the bath fan because it is also laden with humidity (water is one of the main products of gas combustion). The difference being that it is hot, so there's less risk of condensation when venting the single appliance. I'm not saying your chimney will collapse tomorrow, but over the course of several years it will cause problems.
 

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Hello: habe a standard atmosphere water heater (gas) venting into this square brick chimney stack going all the way to the roof from basement. Connection: 4” round double wall duct. Had a furnace replaced with HE.

can I vent into this chimney a 4”duct connected to a bathroom exhaust? I see s remote possibility of a potential backdraft if chimney opening on the top getting clogged and to counter it can and will install a backdraft damper (2 of them) at the start and end of the bathroom vent.

I can’t seem to find a good reason why this would not work.Probably codes in US (I am in NJ) will say no and to which i am not surprised
Are you saying that the chimney has a liner duct all the way up or just a duct connecting the WH to the masonry chimney? Mostly curious since I can't add much. I'm not sure a gas anything vented into masonry chimney would be legal around here. And agree that venting a bathroom fan into that is a patently bad idea.
 

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Discussion Starter · #8 ·
Live and learn: Now I know how the water heater's exhaust operates. Thanks. I also realize what the orphan means. I am surprised there aren't anything in the market like a fan which one can insert into the chimney hole (At the bottom of almost all of them there's a clean-out chute) which runs continuously pushing air upwards. Or add a fan to the water heater exhaust converting it to positive pressure venting perhaps?

Adding a chimney liner is a big deal. Here in NJ its anywhere from $1000 to $1800. Calling the HVAC guy to understand

Question though: If I do put a chimney liner then can I put the bathroom vent? I am assuming the liner will protect from corrosion and with double backdraft dampers chances of CO is limited to none.
 

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Live and learn: Now I know how the water heater's exhaust operates. Thanks. I also realize what the orphan means. I am surprised there aren't anything in the market like a fan which one can insert into the chimney hole (At the bottom of almost all of them there's a clean-out chute) which runs continuously pushing air upwards. Or add a fan to the water heater exhaust converting it to positive pressure venting perhaps?

Adding a chimney liner is a big deal. Here in NJ its anywhere from $1000 to $1800. Calling the HVAC guy to understand

Question though: If I do put a chimney liner then can I put the bathroom vent? I am assuming the liner will protect from corrosion and with double backdraft dampers chances of CO is limited to none.
Is there a reason the fan can't just go out the wall or roof like any other house?
 

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Discussion Starter · #12 ·
What is literally 1 feet away will require extensive work as I have a finished basement and outside walls of the basement is concrete / cinder block.
 

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What is literally 1 feet away will require extensive work as I have a finished basement and outside walls of the basement is concrete / cinder block.
Would you not go out the rim joist. most times we lower the ceiling on a basement bath to make this stuff easier.
 

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Why? Mortar + tiles are protected.

Any water goes to the bottom.

Back draft dampers protect me from CO poisoning.
No, they’re not. What protects them?

No, it doesn’t.

No, they don’t.

I understand a liner is expensive, because it’s adding $1k-$2k to my HVAC estimate also (I would have an orphaned water heater feeding into my large brick chimney).

As someone else said, the erosion of the brick and mortar is a long process that you can’t detect immediately, but it’s long term structural damage.

I’m not sure how an inspector allowed an orphaned hot water heater to pass (and I just learned about this myself recently). People on here are telling you it’s dangerous because it is dangerous. You seem set on taking that risk, which nobody here is recommending.
 

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The water heater and bath fan cannot share the same ventilation to the outside. Period. Liner or no liner. Backdraft damper or none.
It’s against code. It’s dangerous. It’s not a very wise idea.
 

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Discussion Starter · #16 ·
@wrbrb : I contacted 3 chimney flue companies. They all said the same thing. The flue is to protect the chimney, i.e. the bricks/tiles and the mortar used to stack them up. Its like this big round pipe pushed into the chimney from the top. So when you are saying its not protected I am not understanding. They also said the flue is designed to be impervious to water or acidic contents of the water.
 

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Discussion Starter · #17 ·
@roughneck thanks for the response but this is what gets me going. I am an electrical/electronics engineer. Around 3 years ago I had something similar and questioned as to why. All electricians always said is either quoted the code or simply said not in code. So I wrote quite a few emails to NEC. Nothing happened. But suddenly in 2019 an addendum was released citing the exact change I requested.

Here also i see a similar situation. Most will say not in code and that’s it. Code is the Bible, I see in US. Can not and should not be questioned. A liner’s job is to protect. A back draft damper’s job is to protect. Then where is the issue?
 

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My understanding is that a flue is a channel inside a chimney through which air rises. If you have some kind of liner (is that what they're referring to as a flue?), maybe your masonry is somewhat or entirely protected, but it still doesn't help your dangerous draft problem with an orphaned hot water heater. Did you ask the 3 chimney flue companies what they thought about a potential danger?
 

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@roughneck thanks for the response but this is what gets me going. I am an electrical/electronics engineer. Around 3 years ago I had something similar and questioned as to why. All electricians always said is either quoted the code or simply said not in code. So I wrote quite a few emails to NEC. Nothing happened. But suddenly in 2019 an addendum was released citing the exact change I requested.

Here also i see a similar situation. Most will say not in code and that’s it. Code is the Bible, I see in US. Can not and should not be questioned. A liner’s job is to protect. A back draft damper’s job is to protect. Then where is the issue?
Because your creating a potentially lethal setup that has no protection or ability to shut down.
Your bath fan MUST have a separate exhaust.
 

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Discussion Starter · #20 ·
@wrbrb Thanks and yes. The standard US based response. Our job is to install the flue. Yes we guarantee it will protect you from the water (acidic) issue. Code says its required if you have only a water heater. Which means it accounts for the draft problem you are referring to. So we don’t understand what additional danger or issue you see?
 
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