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FROM single-wall TO Type B double-wall?


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I am replacing an existing run of 3" single-wall vent from my old gas water heater with 4" required by the new gas water heater. The old run passes thru a sheet rock wall, but somehow does not have the 10" of clearance required by code. Now that I'm replacing it, I need it to conform to code.

I would like to use Type B where it runs thru the 6" deep sheet rock wall, since it only requires 1" of clearance.

I should mention that the hot water heater's output joins up in a Y connection with the house heater's (gas/hot water) 6" single-wall vent about a foot before the whole thing enters the chimney.

I don't want to do any major construction on the wall to create the desired clearance. I don't want to blow $200 on Type B for the whole run, including a really pricey 6"x4"x6" joint. I also would like to avoid having to pull out the existing mortared chimney joint, and the subsequent widening of the opening using double-wall would require, and then re-mortaring the joint.

I only want to use the B vent where it passes thru the sheet rock. Trouble is, while it's OK to go FROM single-wall TO double-wall, it's not OK to go BACK INTO single-wall FROM B vent pipe.

WHY? It makes no sense to me.

I understand it's code. I understand it's easier to inspect. I understand that for some reason no one makes a transitional adapter FROM double-wall TO single-wall. I just don't understand the logic of it - the physics of it - the thermodynamics of it. What's the underlying reason for the code?

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The single-walled portion of the vent is called a "connector" and is only allowed from the appliance to the B-vent. From there to terminus the B-vent needs to be used because it not only provides reduced heat radiation It keeps the exhaust gases hot enough to retain their buoyancy, without which those acidic exhaust gases stall, cool to dew point, condense inside the vent and then eat through the vent or damage that masonry chimney you're venting into (Which is also a pretty bad idea).

I've seen homeowners try to readapt to single-walled pipe from B-vent material many times. Aside from the fact that the results look jackleg and the vents leaked, the result was loss of gas buoyancy and damage to the vent system. It's a lame-brained thing to do - DON'T DO IT!

Do it right or don't do it at all. Stop complaining about the cost of a product designed to make that system safe and purchase the right components. If it's technically too much for you, loosen the purse strings and hire a tech to do it for you.

ONE TEAM - ONE FIGHT!!!

Mike

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First off, thank you for taking the time to read and respond to this post.

I really do appreciate your input!

Having said that:

DAMN! [:-bigeyes That was harsh!

NO MORE COFFEE FOR YOU - ONE YEAR!!! [;)]

I'm not complaining about the cost, I'm just not made of money. If buying the B vent is pricey, then (with all due respect to the profession) hiring a skilled plumber to connect some Tinker-Toy snap-together B vent system at $100/hr, plus markup on the parts, is pricey-ER. Maybe to an HVAC pro making that $100/hr it's no big deal, but it's a small fortune for me. I'm only pulling down $17/hr, so it would cost me about two weeks' pay to get a pro to do it. It's not that it's beyond my abilities to do it - far from it. I'm just trying to understand the how and why of the situation so I don't screw it up - so to that end, I offer my whole-hearted thanks!

Why is venting into a masonry chimney a bad idea? It's the way the home was built - professionally.

Just for the record, it was a professional plumber and a professional city construction inspector who installed and passed the current run of 3" single-wall that only has about 4" of clearance on one side and 8" on the other side. Until I cut out the sheet rock all around it, it was passing through a hole in the sheet rock that only had about a half inch of clearance. So much for THOSE pros doing a better job.

But the current run (that's been in place for thirty years) is single-wall all the way from both the house heater and the hot water heater. The gasses have never lost buoyancy in all that time - that is to say, there's been no condensation, corrosion, nor CO backing up into the house. I'm just trying to understand how adding a single 1' section of double-wall would screw up the buoyancy of the entire run?

If Type B double-wall is a bad idea the way I was suggesting it be used, then what kind of solution (staying with single-wall vent all the way) would there be to protect the wood studs and sheet rock wall?

I'm asking for a little insight, that's all. (Please be gentle)

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First off, thank you for taking the time to read and respond to this post.

I really do appreciate your input!

Having said that:

DAMN! [:-bigeyes That was harsh!

NO MORE COFFEE FOR YOU - ONE YEAR!!! [;)]

I'm not complaining about the cost, I'm just not made of money. If buying the B vent is pricey, then (with all due respect to the profession) hiring a skilled plumber to connect some Tinker-Toy snap-together B vent system at $100/hr, plus markup on the parts, is pricey-ER. Maybe to an HVAC pro making that $100/hr it's no big deal, but it's a small fortune for me. I'm only pulling down $17/hr, so it would cost me about two weeks' pay to get a pro to do it. It's not that it's beyond my abilities to do it - far from it. I'm just trying to understand the how and why of the situation so I don't screw it up - so to that end, I offer my whole-hearted thanks!

Why is venting into a masonry chimney a bad idea? It's the way the home was built - professionally.

Just for the record, it was a professional plumber and a professional city construction inspector who installed and passed the current run of 3" single-wall that only has about 4" of clearance on one side and 8" on the other side. Until I cut out the sheet rock all around it, it was passing through a hole in the sheet rock that only had about a half inch of clearance. So much for THOSE pros doing a better job.

But the current run (that's been in place for thirty years) is single-wall all the way from both the house heater and the hot water heater. The gasses have never lost buoyancy in all that time - that is to say, there's been no condensation, corrosion, nor CO backing up into the house. I'm just trying to understand how adding a single 1' section of double-wall would screw up the buoyancy of the entire run?

If Type B double-wall is a bad idea the way I was suggesting it be used, then what kind of solution (staying with single-wall vent all the way) would there be to protect the wood studs and sheet rock wall?

I'm asking for a little insight, that's all. (Please be gentle)

If you think he was too harsh, it might surprise you that this guy can advise like few others can on this forum.

You're lucky to get his advice. He's precisely on spot with your issue, as usual.

Stick around, you'll see what I mean.

Marc

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Yup, you're right.

I've actually "lurked" around this site and read some of Mike's posts. I was both amazed and very happy that it was hausdok who answered my post first.

That's why I opened my reply with "thank you," and said that I appreciate the input and again offered my whole-hearted thanks.

But in answering someone who's seeking advice, maybe not so much of the "stop complaining" and the "lame-brained." The student is already in a subordinate position; no need to rap him on the knuckles for being inquisitive.

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Without apologizing, 'cuz I don't think I said anything that I need to apologize for,

The simple answer is just run B-vent all the way from the collar to the outside. It will retain the heat you need to maintain buoyancy it will allow you to reduce the clearance around it to combustibles.

A water heater venting into a big chimney is condensing water all over the place whether you realize it or not. Why is a straw you use to drink out of very small in diameter? Why not two inches in diameter? Answer-try sucking liquid up through that two-inch wide straw and see how hard it is compared to sucking it through a narrow straw.

Now imagine the air passing over that chimney causing, if the stack is properly positioned, low pressure above the vent that helps the water heater to draft. It pulls a whole lot better when it's passing over a 3 - 4 - 5 inch B vent than it does when it passes over the gaping maw of a masonry chimney flue. Most of that water heater exhaust probably cools to dew point about a foot or two from where the B vent ends and it enters the flue; and then it just clings to the sides of the flue, eats it up and eventually turns it to masonry mush. If the chimney passes up through the center of the house where it's not as cold as a stack exposed on the outside wall of the house, it might not be as bad as it would be on the outside wall of the house 'if' the flue isn't way oversized. For the typical 40,000 Btu water heater - just about every masonry flue is oversized.

As far as I can tell from what you've posted, YOU have not entered the realm of lame-brainededness. I was saying that sticking a single-walled vent into the middle of a vent system after a B-vent is installed is lame brained. I was urging you not to become one in my own inimitable fashion.

It might surprise you to learn that just about every furnace I see from the 70's and 80's and well into the 90's and up to about 2006 is installed wrong because around here most are in unheated garages and the code had said for many years that "connectors" in "cold" areas were supposed to be double-walled material. The HVAC industry has rigging the books for years by ignoring that little rule around here because they made sure they'd increase the frequency of their repeat repair business. The number of condensate-damaged furnaces, connectors and vents I've seen is mind-boggling.

Then some numb nuts decided to eliminate that rule altogether and the number of Cat 1 furnaces installed with single-walled connectors increased around here - and so did the number of damaged appliances.

If you have the skills do the work yourself; but use the correct components. If you're smart, you'll extend that vent through and up that chimney and cap the old flue around the liner in order to turn that masonry flue into warmed space that will keep the flue liner warm instead of it being a condenser.

ONE TEAM - ONE FIGHT!!!

Mike

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There's nothing wrong with venting your gas-fired water heater into a masonry chimney - as long as it has a properly installed and correctly sized terra cotta liner and it is shared with a gas-fired heating system.

There's nothing wrong with single-walled vent connectors used in a conditioned space (I'm guessing this is in a basement - maybe finished) between natural draft, gas-fired equipment and the chimney.

Single walled vent connectors from natural draft, gas-fired equipment do not need 10" of clearance to combustibles. Only 6", unless the appliance is one that has a gas conversion burner.

There are "wall thimbles" that can be used to pass single-walled vent connectors through a combustible wall assembly.

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First of all, you really should get a Level II inspection of the chimney before attaching the new appliance. Also, the common vent (chimney) will need to be confirmed as the proper size for the two appliances. Between these two items, you will need a listed liner. Next, if the breaching where the connectors attach to the chimney are in unconditioned space then those connectors must be all B-vent. If you are penetrating a combustible wall then you must use B-vent as prescribed in the listing which is only continuous--not just a short length. Hausdok has given you some pretty good answers. Oh, yeah, what is the total lateral offset and vertical height of the chimney? Can you maintain 1/4" per foot slope up to the chimney?

Instead of trying to common vent the WH with a furnace, which can be very dangerous, you always have the option of installing a power vented water heater and venting out the sidewall with polymeric pipe. If you must use the chimney, it might be cheaper but will definitely give better venting if you relocate the WH into the CAZ with the furnace and eliminate that long cold lateral offset. BTW, for a long lateral offset, you may have to increase your vent connector larger than the draft hood collar--you WILL have to increase it if your vertical vent rise is less than 3 feet. You will probably also have to increase the manifold (your 'Y) so refer to the sizing charts in the code. Once it is all connected, have a certified pro perform combustion analysis to ensure proper venting. Or you can just breathe deeply. No offense but legally installed water heaters perform poorly enough but going out of your way on the cheap is the Kervorkian option. A draft hood equipped gas water heater is the most dangerous appliance in most homes. So called 'pros' are bad enough installing them but this is one DIY you should defer to a pro. BTW, the clearance on a 4" single walled pipe would be 16"> 6" each side plus the pipe diameter.

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Bill, Hearthman, Marc, and Mike, THANK YOU! THANK YOU! THANK YOU!

I'm very grateful for your valuable insights into this issue. I've been all over the web with these questions and all the answers have been bumbling and useless. It's refreshing to listen to folks who have accurate information and solid training. You guys are the best! You've given me a lot to digest.

So, just to clear up a couple of issues, the entire run of both the house heater and the hot water heater are inside the envelope. The chimney is in the middle of the house. Just as Bill guessed, it's all in our conditioned downstairs (not a basement, as my late Father-in-Law always insisted). It's finished, with drop ceilings and flooring, heat and air con, etc.

The system has been in place with both house heater and hot water heater sharing the masonry chimney for just shy of fifty years (my wife corrected me). Again, in all that time, there has been no corrosion of any of the single-wall vent.

The house heater was just replaced two years ago by a company that's been in business since 1947, and they inspected the chimney and installed the new 6" single-wall from the heater and a new Y joint, as well as the mortared seal to the masonry chimney.

I apologize for troubling all of you since I was told by no less than three "pros" (as well as the folks that sold me an assortment of type B) that the requirement was 10" beyond the walls of single-wall vent, which would be a total of 24". It makes much more sense that 6" all around, plus the 4" vent is correct, since it adds up to 16" spacing of the studs (though they're 16" on center so there's ostensibly 7/8" of pine stud on either side impinging on that space ... just thinking out loud).

Thank you all again. I really wish there was some way I could repay you all. I guess the best way I can repay you is to make sure the job's done right and to code.

You guys really are the best. Thanks!

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A couple of thoughts to consider:

. . . it's all in our conditioned downstairs (not a basement, as my late Father-in-Law always insisted). It's finished, with drop ceilings and flooring, heat and air con, etc.

That's good, but it's still a basement. The fact that it's finished doesn't change that. If it's partially or completely below grade, it's a basement, albiet a finished one. The fact that it's a conditioned space makes a big difference in what is and isn't appropriate for venting.

The system has been in place with both house heater and hot water heater sharing the masonry chimney for just shy of fifty years (my wife corrected me). Again, in all that time, there has been no corrosion of any of the single-wall vent.

Don't let that make you too complacent. The gas appliances of fifty years ago - and even those of 20 years ago - were less efficient than those of today. They allowed a lot more heat to enter the venting system. This kept things dry and allowed for a large margin of error. Modern appliances send less heat up the vent (in this case, a chimney) and allow a lot more condenstion to form. Just because a chimney performed well in the past doesn't mean that it will in the future.

Since it's a conditioned space, a single wall vent connector is considered acceptable, but a B-vent would be better all around, especially if you ran it all the way up through the chimney. There would be less risk of back drafting, and less risk of condensation damage.

As for the clearance at the wall, as far as I know, single wall vent connectors are not supposed to pass through partition wall at all. The provisions for 6" clearnace, thimbles, etc, are intended for when a single-wall vent passes through an exterior wall or roof. If the vent connector is inside a building, it's supposed to go from the appliance to the main vent (or chimney, in this case) without passing through a wall, floor, or ceiling. The IRC reference for this is G2427.10.14.

By the way, if I had responded to you first, instead of Mike, I would have been a lot harsher. This venting stuff might seem like an expensive and unnecessary pain in the neck to you, but improper venting can be deadly. It's serious stuff and, if you don't understand it, as you proudly proclaim in your original post, you really, really should not be messing with it. (That's two "reallys.")

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Well, I really didn't come here to talk about demeanor, but, since it keeps coming up . . .

I'm here because I'm taking it seriously. I'm in the process of making decisions. Y'all can't have known this, but, I've spent LITERALLY months trying to understand what forces are in play. I think it's almost as bad to throw money at something and blindly trust an unknown quantity with a truck and some tools as it is to DIY uninformed. So, whichever road I choose, I have no intention of traveling that path in ignorance.

As far as my "proud" proclamation of ignorance, I remember a sensei once telling a student he knew "less than nothing;" he could not be taught because he didn't know that he didn't know. You have to recognize your ignorance before you can seek the tutelage of a master - it comes from a place of humility and respect, not pride. Someone asking for help is putting themselves in a vulnerable position, so there's no need to smack them down.

As Mike's signature says "One Team, One Fight," we're (hopefully) all on the same side here. I have no interest in being cheap or cutting corners at the expense of ruining my home, or worse, killing my family. On the other hand, I'm also putting a child through college, so I'm not going to blindly write checks for unnecessary expenses. And IF I can DIY some portion of the job and save some portion of that $100/hr, I most certainly will. At the same time, I understand that, like a doctor, you often are not paying for what he does, but what he knows.

And just for the record, Mike, I never asked for an apology, and none was ever necessary. My comments where simply meant as a little friendly chiding, as I hoped the use of the silly emoticons would demonstrate.

WHEW! Now to the actual issue at hand.

I'm psyched that appliances are more efficient now. Our house heater is just two years old, and professionally installed. The heater we're replacing is only six years old. In fact, our original replacement choice was a 50gal tall, but, it was too tall to give us the necessary run:rise ratio. So we had to settle for a much less efficient, more old-school 40gal short. So the replacement is almost identical to the model it's replacing.

By my reading of G2427.10.14, G2427.7.4, and G2427.10.15 this thing never should have been where it is. It's funny, but my original instinct was to put it in the same room as the house heater. The chimney is in that room, so it would be an extremely short run. Space is kinda tight, though.

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Was your old furnace draft hood equipped and the new one fan assisted? If so, you'll need a liner. BTW, you can no longer cement a single walled galvanized steel connector into a chimney. It must be stainless steel or in a sleeve that makes it easily removed for inspection. The fact you had single walled connector last 50 yrs tells me how inefficient your old equipment was! BTW, if your chimney should become blocked, the furnace will continue to fire venting out the water heater draft hood bypassing three safety controls on the furnace. You still need that Level II inspection. The HVAC contractor "looking" at it is nowhere close to a level II. Also, get low level unlisted CO monitors for your home.

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Neither of the water heaters are fan-assisted. That's what I had originally wanted because of it's high efficiency and the fact that it would vent right out the side wall, so no duct work at all.

That Rheem sounds great! How do they do that; how can it recover so fast and still have lower operating cost than a 50gal? Or are they just comparing it with a really outdated 50gal? Reading the specs though, it's 9" taller than the 40gal we're going with now, so it might be a tad too tall. The 17" diameter would be great for using in the same spot as the house heater, though. But if it's a shorter horizontal run, I mean, it would practically be going right into the chimney if we put it in the same room with the house heater, we might be able to get away with that height. I'll have to take some measurements. Still think it may be just a bit too tall.

Plummen, I haven't forgotten you. I'm having a technical issue with a photo, but I'm workin' on it.

I can't thank all of you enough for your time & input.

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The house heater was just replaced two years ago by a company that's been in business since 1947, and they inspected the chimney and installed the new 6" single-wall from the heater and a new Y joint, as well as the mortared seal to the masonry chimney.

I have contractors tell me how long they've been in business, after calling out defects, quite often. It doesn't impress me with, you know, that imperfect practice.

Plus, I'd guess you just had a minimally trained guy working for the company do the install. It's not the company, it's the employee that does the installation. If you prove it was done wrong, contact/ complain to the owner of the company.

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That Rheem sounds great! How do they do that

High BTU output burner. Most 40 and 50 gal. water heaters only have a burner rated at around 40k btu's, while the Rheem has a much higher rated burner, so there's a much quicker recovery rate.

There's less standby loss with a water heater that has a smaller tank, and newer water heaters of course have better insulation levels (not that any gas unit is great, due to the large flue up the center).

This water heater is at the top of my list for when I need to replace mine.

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The new house heater was installed by a relatively large, local, family company that's been in business since 1947 and one of the two brothers (in his late 50s, so a seasoned vet) who currently own/operate the company, and three other guys came in and took the old behemoth out and installed it in one day.

Yeah, the Rheem won't fit where it's got to go.

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