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Connecting furnace/water heater single B vent flue


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Please see attached picture. A furnace (on left) and water heater (on right) are connected to a single single wall pipe which feeds directly into B vent pipe at a distance of about a foot from the single wall pipe. The B vent pipe cannot be seen in the picture but runs behind the furnace for about 6 feet to a newly installed B vent chimney flue (run inside an old clay lined chimney). Is it okay to connect both the furnace and water heater to a single pipe as shown in the picture? When both appliances are running will a backdraft be created through the water heater? Is this safe? Thanks for your help

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You can combine 2 vent connectors into a common vent connector, provided it is sized and installed correctly.

What's shown in the picture, with the WH vent connector shoved into a hole cut in the side of a wye, is just really wrong. The slope of the 2 vent connectors doesn't look right from this angle. I'd like to see the rest of the vent system to see what else was done.

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I had a chimney company run a new stainless steel liner down my chimney and this is how they connected the furnace and water heater to connect to the liner in the chimney. At the time, I suspected there may be something wrong with this setup but not being an expert, did not question. Further research, on sites such as this, made me suspect potential problems. Previously, the water heater and furnace had 2 separate vent pipes running to a clay lined chimney with the water heater vent pipe above the furnace vent pipe. I believe this was a good venting situation. Now, there is only one connection into the stainless steel chimney liner and the picture posted is how the chimney lining company solved the venting of 2 units (furnace and water heater) into 1 liner opening. I have no intention of going back to the chimney liner company for a solution to this issue. I suppose my path forward is to call my HVAC company and have them examine and correct the issue. Do you have ideas as to how I will be able to successfully vent both water heater and furnace into one chimney liner opening? Any help would be appreciated. I just want to be able to speak intelligently with whomever I hire to resolve this issue. Thanks.

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Run them both into a (new) wye and increase the size of the "exhaust" side the next size up.

An HVAC tech may determine that they need to resize both flue connectors, and I hate to say it, but possibly even the liner. Anyone that would mangle together an assembly like that might not know they have to size everything based on the output of the appliances.

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I know that you say get an electric hot water heater with a smile. But, is this a viable option as the gas hot water heater I currently have is 20 years old. Does this potentially solve my problem? Is it a bad idea to replace a gas hot water heater with an electric hot water heater? Thanks.

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I wouldn't jump to on tankless without knowing more. They're a pain in the ass on some houses.

Electric is a viable option. I own both types in different buildings and I've not ever been able to determine if electric costs more to operate than my gas water heaters.

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There's nothing fundamentally wrong with venting them together into the chimney. It's just that this guy did everything wrong.

From what I can see in the pictures, it looks like the biggest problem will be height. The two vent connectors should join high in the room. Also, the water heater vent connector needs to go up about 12 inches vertically before it turns to run horizontally.

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Also, the water heater vent connector needs to go up about 12 inches vertically before it turns to run horizontally.

I have read about a 12" minimum rise for priming but can't find the coded reference. Is this something you would find in the tables?

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Also, the water heater vent connector needs to go up about 12 inches vertically before it turns to run horizontally.

I have read about a 12" minimum rise for priming but can't find the coded reference. Is this something you would find in the tables?

Yes but, as I recall, it only applies when venting the water heater with another appliance.

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