# Guessing wrong sized vent



## AKdaplumba (Jan 12, 2010)

In the mech room is a boiler and HWT totaling 100BTU. The C vent where the 2 connect is covered in rust and a white chalk. the B vent is 5'' while the C that connects to the B is with a 5x4x4 tee. The length is about 30 ft. I think the B vent should be 4'' all the way to the top. Since I don't have a code book on hand does that sound about right?


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## BC73RS (Jan 25, 2014)

I just checked my BC code book and for two or more appliances at 30' the common vent can be 4".


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## Catlin987987 (Nov 12, 2010)

AKdaplumba said:


> In the mech room is a boiler and HWT totaling 100BTU. The C vent where the 2 connect is covered in rust and a white chalk. the B vent is 5'' while the C that connects to the B is with a 5x4x4 tee. The length is about 30 ft. I think the B vent should be 4'' all the way to the top. Since I don't have a code book on hand does that sound about right?


When you see bad venting when connected to a boiler, I always check to see what temp the boiler is running. If its too low condensing, it always rots out the venting. Atmospheric boiler should always be set so min 130F return temperature.


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## Otobeme (Jul 9, 2015)

Post a picture. Heat will not cause rust. Chemical reaction of combustion onto zink. If the flue is cold (winter) and hit with heat it will cause condensation. Check the cap on the roof has not been blown off and what Cat said. Make sure CO detectors are in place and functional. 

How much horizontal venting? fresh air for combustion is good?


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## plumbdrum (Nov 30, 2013)

Otobeme said:


> Post a picture. Heat will not cause rust. Chemical reaction of combustion onto zink. If the flue is cold (winter) and hit with heat it will cause condensation. Check the cap on the roof has not been blown off and what Cat said. Make sure CO detectors are in place and functional. How much horizontal venting? fresh air for combustion is good?


Bingo


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## AKdaplumba (Jan 12, 2010)

It looks like a straight vertical shot to the roof. It's a duplex, the other unit of the duplex doesn't have the problem and I am assuming it's done the same way.


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