# Flu for the water heater - What are the rules?



## zootjeff (Jul 11, 2007)

I have a 40 gallon water heater.

What are the rules for the flu? I have 6" b vent that goes about 12' to get above the wood chimney.

What are the rules in the garage for the B vent transition to flex duct to connect to the water heater?

How far from the wall does the B vent need to protrude?

Can I use 6" for most of the run if it is 3" coming off the water heater?

How far does the Bvent need to come down into the space before the transition?

Thanks,

Jeff


----------



## plumber Jim (Mar 30, 2008)

That sounds kinda confusing. If i get you right you have a water heater that has a 3" flu and connects to a 6" b vent pipe. and you want to use a flex type pipe. Well.. no can do. you can't use that metal flex they sell for dryers etc. . You really need to have a pro do this. CO is serious and can kill you and your family easy if you do it wrong. Am i trying to scare you? yes i am because this is very serious. people die from this. PLEASE have it done by a licensed person. If you do the other stuff and just leave that venting to a pro you will be MUCH better off and safe.


----------



## zootjeff (Jul 11, 2007)

plumber Jim said:


> That sounds kinda confusing. If i get you right you have a water heater that has a 3" flu and connects to a 6" b vent pipe. and you want to use a flex type pipe. Well.. no can do. you can't use that metal flex they sell for dryers etc. . You really need to have a pro do this. CO is serious and can kill you and your family easy if you do it wrong. Am i trying to scare you? yes i am because this is very serious. people die from this. PLEASE have it done by a licensed person. If you do the other stuff and just leave that venting to a pro you will be MUCH better off and safe.



They make stainless steel single wall flex pipe which is ok to use right above the water heater, but it can't transition to the drywall and there is some min spacing for it to transition to B vent from the celing as I understand it. I'm trying to figure out if I should use a box transition or a wall thimble. 

What I'm unclear on is what is the best transition to use into the drywall of the ceiling. A thimble or a box or is it ok for B vent to go right up against the drywall like the previous "pro" did?

I'm not shopping at Home Depot for this stuff. I'm going to a JohnStone or a Johnson Air.

http://www.johnsonair.com/propertydetails/17 Gas Vent.pdf

I can get any of these parts:

http://www.duravent.com/?page=ts.php


A more specific question is: I have a 5/8 drywall celing above my water heater. There are 2/6 rafters above it and loose fill insulation in the attic. What is the best transistion to use in 3" to get into the attic and then transistion to the 6" Bvent. 

-Jeff


----------



## Michael Thomas (Jan 27, 2008)

A bit of a read, but if you really want to understand how it _should_ be done see http://www.duravent.com/pdf/shbook.pdf .


----------



## zootjeff (Jul 11, 2007)

Michael Thomas said:


> A bit of a read, but if you really want to understand how it _should_ be done see http://www.duravent.com/pdf/shbook.pdf .


Thank you! That's what I needed!


----------



## zootjeff (Jul 11, 2007)

Here is what I wound up doing:


I had this crappy flu that was rusting out, the Y was cracking at the seam:










Never really got a good picture, but here you can see the Bvent right up against the drywall as it comes into the garage from the attic. This was violating the 1" to combustibles. The vent in the attic was mostly good 6" b-vent but there was a single-wall 6" section 24" long that connects between two b-vent 45's that a "pro" let get by and the inspector didn't do a thing about. This single wall was also right against paper insulation backing.











Another view










Made a nice little box to support the firestop and drywall:










Added drywall:











Connected the old B-Vent to the new Simpson Duravent that I got from my local Johnson Air Supply, with temporary flex vent to tide me over..











All finished with transitions and b-vent











And another shot










All the venting in the attic and almost all the way to the water heater is now b-vent. I also made sure I have 1" to everything around the b-vent.

I miss-calculated how much bvent I needed so I still have the single wall for the last 6" section. I currently have 3" transition -> 45 > 45 -> Draft Hood -> singlewall 90

I might get another b-vent 90 or take back a 45 and get a 6" section and a 90... For now this is working though..


----------



## zootjeff (Jul 11, 2007)

plumber Jim said:


> CO is serious and can kill you and your family easy if you do it wrong.


Do you still think I'm at risk here? If so I'll hire a pro to check it out.


----------



## Gary_602z (Nov 15, 2008)

I would be looking at the pipe for your T&P valve, I don't think what you have would meet code.

Gary


----------



## zootjeff (Jul 11, 2007)

Gary_602z said:


> I would be looking at the pipe for your T&P valve, I don't think what you have would meet code.
> 
> Gary


Does it need to go all the way to the floor?


----------



## Gary_602z (Nov 15, 2008)

Someone else will know for sure but I think it is like a foot or six inches from the floor.

Gary


----------



## plumber Jim (Mar 30, 2008)

zootjeff said:


> Do you still think I'm at risk here? If so I'll hire a pro to check it out.


Well, I can't see it all but i am glad to see you didn't use that flex stuff and used b-vent and got the clearances. If you are only going to have that water heater on that vent then 6" is too large. if I am looking at the old pictures right they had 6" because it was for the furnace and the water heater.


----------



## zootjeff (Jul 11, 2007)

plumber Jim said:


> Well, I can't see it all but i am glad to see you didn't use that flex stuff and used b-vent and got the clearances. If you are only going to have that water heater on that vent then 6" is too large. if I am looking at the old pictures right they had 6" because it was for the furnace and the water heater.













Total run length is about 16 feet from top of water heater to top of vent cap. I'm using the existing 6" vent that was installed when the house was built when the furnace was not high eff. When I had the furnace done in 2002 the installer doing the furnace just put that cap on the y and left the water heater hooked up to the existing 6" vent. I just made it all B-vent and re-did the transition into the garage. Am I going to have a problem with a 6" vent or is it just "overkill." According to the sizing tables it doesn't seem like there is a min btu rating on 6" with the "natural" draft venting. People may turn off their furnace and the water heater will still run on a shared vent system. How would this be different? Also, would they make a 3" to 6" B-vent transition piece if the code does not allow it to ever be used? What I have is commonly called an "orphaned water heater".

I think the problem is if your flu has too much inner surface area to maintain enough heat to maintain a draft and you'll have the gasses going up but cooling off too much and possibly back-drafting back down, thus creating a CO problem. Not to mention the water condensing on the cold surface and creating a water/rust problem. My water heater is pretty in-efficient, on the energy guide sticker, mine is the lowest efficiency in it's class.. That means plenty of heat going up the stack to keep the 6" toasty, right? 




One source (http://www.askthebuilder.com/B205_Hot_Water_Heater_Venting.shtml) suggests: 

"The inside cross sectional area of the flue should be no greater than seven times the cross sectional area of the flue pipe that leaves the heater."

But this is for brick, not b-vent, but lots of sources site the 7x rule

With a 3" source I have 7 square inches
With a 6" vent flu I have 28 square inches
28/7 is 4 times as large. That suggests I could have vented my 3" water heater with as large as 8" vent.

http://www.hartandcooley.com/vent/sizing%20guides/Gas%20vent,%20chimney%20sizing%20&%20application%20guide.pdf

These guys also mention the 7x rule on PDF page 11 (doc page 9).



-Jeff


----------



## 130 plumber (Oct 24, 2009)

Gary_602z said:


> Someone else will know for sure but I think it is like a foot or six inches from the floor.
> 
> Gary


 
6'' :thumbsup:


----------



## zootjeff (Jul 11, 2007)

Ok,

I'll sweat some extra pipe to the pressure valve pipe and route it back away from the front. Sounds like the code is there so that if you have an explosive discharge from the valve, you want the spray as far away from people as possible. With the pipe 12" below the base of the heater, I need to make sure I have a way to remove the pipe if I ever take the water heater out to play with it. It seems like the valve can twist in place to give me a service path to twist into the valve.


----------



## Gary in WA (Mar 11, 2009)

I'm not HVAC or plumber, but don't the elbows, short straight pipe and appliance vent collar require 3 screws in each joint? Put insulation on both water lines. Install earthquake straps tied to wall studs.If you want really safe, install a bollard in front of tank. And as mentioned, run the TPRV discharge away. If it went off now, it could splash off the support floor and put out the flame under the shield letting the gas fill your garage for a surprise when you came home. Page #6: http://www.codecheck.com/cc/images/CC5thEdSample.pdf

Be safe, Gary


----------



## zootjeff (Jul 11, 2007)

GBR in WA said:


> I'm not HVAC or plumber, but don't the elbows, short straight pipe and appliance vent collar require 3 screws in each joint? Put insulation on both water lines. Install earthquake straps tied to wall studs.If you want really safe, install a bollard in front of tank. And as mentioned, run the TPRV discharge away. If it went off now, it could splash off the support floor and put out the flame under the shield letting the gas fill your garage for a surprise when you came home. Page #6: http://www.codecheck.com/cc/images/CC5thEdSample.pdf
> 
> Be safe, Gary


Thanks, I'll fix it ASAP. My water heater is actually sealed in the front under the front guard. There is a pilot window you can look through, there is a screen mesh under the water heater where the combustible air comes in, so this is less likely to blow my house up in the event of a discharge, but there is still the risk, I will not take it lightly in any case. I don't want to scald anyone if they walk past either.

Regarding the venting, I'm going to get another section of b-vent to replace the single wall, then the appliance collar will go right to the vent hood and I'll put in the 3 screws..

-Jeff


----------



## zootjeff (Jul 11, 2007)

OK,

I added the Thermal Valve pipe so it routes to within 6" of the ground.

Also got the furnace connected back together.


----------

