Gas Boiler Vent Questions

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Old 01-14-18, 11:14 AM
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Gas Boiler Vent Questions

Hi everyone was wondering if people could offer up some suggestions regarding my hot water and boiler vents. I believe the hot water needs to be above the boiler or Tee'd into the boiler. I'm not to keen in breaking another hole into the chimney to move the HWT up.

So looking for options and opinions. Pics are attached.
 
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Old 01-14-18, 12:20 PM
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I was told many, many years ago that proper venting was the boiler, the largest appliance, was on the bottom and the water heater was always on the top. I can not tell you if this is a code requirement but it was what I was taught.
 
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Old 01-14-18, 12:30 PM
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My home was built in 1959 and the gas furnace is just below the water heater vent. I've spent some time looking thru the gas codes and haven't found any mention of which one should be above the other.
 
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Old 01-14-18, 01:12 PM
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I'm thinking I can tee or wye into the 6"boilers duct work...but not sure
 
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Old 01-14-18, 02:54 PM
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Based on what I've been reading... I would agree with a tee.
Are you having problems with the way it's setup now ?
 
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Old 01-14-18, 04:20 PM
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I think there may be some backdrafting problems. Either way just wanted it fixed the right way
 
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Old 01-15-18, 04:07 AM
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You can not "T" into the boiler's flue pipe without increasing the size of that pipe before that "T". Also,I was taught that the largest pipe was always on the bottom and the smallest on top so that if the chimney were to plug from falling debris the larger pipe would not plug as quickly as the smaller pipe and that the problem could be caught during the normal yearly service call. AS I said in my first post I never knew if there was a "code" for this. The old guy that stated this said that it was just done that way and was the only "common sense" way to do it.
 
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Old 01-15-18, 01:52 PM
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Typically the issue you're trying to avoid is the smaller device having trouble getting a good draft because the chimney is sized for the larger device. So, DHW above might be a little better, because the boiler would tend to warm up the entire length of chimney for the DHW, and your metal flue for the DHW will have more pitch. But, I don't think it would matter much.

More important is that I would make sure you're getting a good draft for the DHW when running alone on a cold chimney. If you are, then probably not much to worry about. If you have poor draft, and especially if you see condensate and corrosion on the DHW heater and its flue, then that's a flag that you're not drafting the DHW well. And probably changing the metal flue position isn't going to fix that issue.

*Although I've managed a lot of HVAC projects, I'm not an HVAC tech, so others may have a better answer. If you're relying on me, change your CO detector batteries.
 
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Old 01-15-18, 01:57 PM
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Good points.

Actually looking again at the first picture..... there doesn't appear to be any pitch in the water heater flue line. I'm wondering if the short piece of vent directly over the water heater should be shortened to increase the pitch.
 
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Old 01-15-18, 05:47 PM
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....there doesn't appear to be any pitch in the water heater flue line. I'm wondering if the short piece of vent directly over the water heater should be shortened to increase the pitch.
This is what I would do before trying anything else.
 
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