Atmospheric water heater venting

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Clutchcargo

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Venting has been a chronic problem with my NG water heaters.
This is the second one that displayed the same venting issue.
On startup, you can see by the melted plastic bits that venting spills until draft is established.
This is joining the 6" boiler venting (also atmospheric) before entering the chimney. Chimney goes from basement to the roof (2 story house).
Would upping the water heater venting to 4" solve this problem?
The current water heater is not long for this world, it's a 9 year warranty on year 10 of service.
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John Gayewski

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Have you watched this closely under different conditions? Basically does it spill exhaust without the boiler running?
 

Breplum

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The cost to run 4" double wall two stories begs the question, why not go fan assisted WH or upgrade to tankless condensing WH 96% effecient and use PVC to sidewall vent.
I am not specifically recommending, but it would pay for itself to upgrade completely and use a combi if the home heating load is small enough.
 

Clutchcargo

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The idea was to replace the 3" venting with 4" to the existing T from the boiler, not to the roof, there's not enough room in the flue for two vent pipes to exist.
 

Jeff H Young

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40k btu dosent need a 4 inch vent , I guess some asssumption that bigger is better might be true but Im not going there. its cheap as heck to try though. I have no real experiance with those chiminys dont know if they draw much. your vent is very flat with no verticle rise before first 90 so Im not suprised it has issues. you might check for C.O. in area
 

Clutchcargo

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In pretty sure it's your basement is too small. Is that window open all the time? If so how big is it?
Don't know why I didn't think of this before but I just checked with a stick of insense. The basement must be in negative pressure... it's pulling air out from the vent.

The plumber who installed the original WH 16 years ago installed a 6" damper in one of the windows.
 

Jeff H Young

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How about trying opening a second window 6 inch round damper is too small. I don't think going flat right off the collar helps
I don't think you answered question on whether w/h functions properly when furnace is off. That's a very important one john asked
 

John Gayewski

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Don't know why I didn't think of this before but I just checked with a stick of insense. The basement must be in negative pressure... it's pulling air out from the vent.

The plumber who installed the original WH 16 years ago installed a 6" damper in one of the windows.
Height of the basement ceiling? Like I said I think your area is too small, but I need to know how small. That way I can tell you if your 6" (round or square?) damper is big enough.

Also need to know length of vent connectors, their size, the length and diameter of the common connector manifold. Height of chimney, dimensions if chimney of there's no liner, is there's I liner what's the diameter? All of that will tell me if you have properly size makeup air and venting.
 

John Gayewski

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Height of the basement ceiling? Like I said I think your area is too small, but I need to know how small. That way I can tell you if your 6" (round or square?) damper is big enough.

Also need to know length of vent connectors, their size, the length and diameter of the common connector manifold. Height of chimney, dimensions if chimney of there's no liner, is there's I liner what's the diameter? All of that will tell me if you have properly size makeup air and venting.
I'm pretty sure one of the above perameters is off a bigger vent connectors for the water heater might help, but I can't tell you that unless I have all of the info. Makeup air is first.
 

Clutchcargo

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Sorry for the omission. Basement height is 78 inches. The windows themselves are never opened... just the 6" round damper allows air in.
The water heater conx is 4' before it joins the 6" boiler vent. From there it's a straight shot up the chimney maybe 26-27 feet to the top of the chimney cap. The event is 6" from the boiler all the way up.
 
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Jeff H Young

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Also might be helpful to know if it vents ok on just the water heater?? I'm coming up with a demand for 56 square inches of combustion air. 2, 6 inch round intakes 1 square inch per 3000 btu's from one source 4000 from another. I still think the rise in elevation is not enough but I've put 90s right on top of the w/h before but with far more pitch
Just running water heater I don't see the need for more air or a bigger basement but I suspect there is more to it than just the waterheater not working alone. Maybe your damper doesn't function either
 

John Gayewski

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From what I found your vent connector for your water heater does need to be 4".

Literally every other factor in this setup is right at the minimum. Including the 6" fresh air pipe that your plumber installed.

Your basement is half the size it needs to be without that 6" fresh air pipe. And it's right at the limit
 

John Gayewski

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also might be helpful to know if it vents ok on just the water heater?? Im coming up with a demand for 56 square inches of combustion air. 2, 6 inch round intakes 1 square inch per 3000 btu's from one source 4000 from another . I still think the rise in elevation is not enough but ive put 90s right on top of the w/h before but with far more pitch
just running water heater I dont see the need for more air or a bigger basement but I suspect there is more to it than just the waterheater not working alone. maybe your damper dosent function either
He said it was drafting. Take out your code book and flip to appendix j
 

Jeff H Young

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He said it was drafting. Take out your code book and flip to appendix j
Thanks john recalculated and he needs 27 square inches of additional intake (which he has) and your right that's minimum should work then right? especially if he is just using water heater alone then it should work fine no problem at all . I had only figured on the outside air and not accounted for the space of 4368 cu ft of basement with a need of 8500 . agree 40k heater doesn't need a 4 inch vent that's why they come with 3 inch collar.
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