Vent Pipe For Boiler: How Far Into Masonry Chimney?

PGB1

I apologize if this is elementary, but information online conflicts.

The chimney of concern is brick with a clay liner that I think is 9 x 13". (I can't climb anymore, so I can't measure on roof.)

Our boiler vents using 5 inch diameter 26 gauge vent pipe. (100,000 btu input, cast iron sectional, not power vented, not condensing. From about 1945.)

The existing vent pipe was 30 gauge and rusted through where it enters the masonry chimney. Also in the chimney is the vent for a water heater. It is 26 gauge 3" diameter and enters the masonry separately, a few inches above the chimney vent.

Of concern is how far the new 26 gauge pipe extends inside the liner. I've read "flush to the inside of the liner", "an inch into the liner", "to the center of the liner", "shorter than the water heater pipe" and "past the end of the water heater pipe".

Thanks For Advising,

Paul

PS: A metal liner is not possilbe at this time, but hopefully in the future.

Jamie Hall

Two appliances into the same flue is very bad practice. It may not even be permitted in your area.

OK. Having said that, the stove pipe or other appliance vent should project slightly into the flue, but not excessively. A good chimney sweep person will get it right.

PGB1

Thanks Jamie Hall for your advice. I appreciate it.

Going with what you advised about 2 appliances into one flue, when it is time for a liner should I specify separate liners for each appliance? They would both still go into the same masonry chimney. (Assuming they fit)

In our city, for existing installations allowed are two into one flue if neither is power vented. They also allow one to size a vent pipe large enough for both into the masonry and then put each appliance into the larger pipe. I haven't the distance from chimney for that.

Thanks Again,

Paul

EdTheHeaterMan

As far as @Jamie Hall 's insight is very valuable and he has many more years of experience in all types of systems. There are many occasions that a water heater with a 3" or 4" vent connector is allowed to enter the same masonry chimney as an oil or gas space heating appliance that is vented just below it. The common knowledge is that the Oil Fired appliance must enter the chimney below the Gas fired appliance. It is done all the time. When venting multiple gas appliances into a common vent, the manufacturer of the appliances offer guidelines that will specify the common pipe size that all the vent connectors will be connected to.

As for how far to insert the vent connector (26 Gauge galvanized pipe is called the connector) the end of  the connector must be flush with the inner wall of the liner. And it should be sealed on the inside where it connects to the liner.

Jamie Hall

@EdTheHeaterMan , who is a much better tradesman than I ever was or will be, is right. Sort of. I know something about chimneys and venting, but don't have his level of experience or knowledge! Go with what he says.

Bob Harper

NFPA 211 calls for the vent connector to be flush with the inner face of the flue. The junction with the flue tile must be chinked with furnace cement for a tight seal.

The connector must be removable meaning you cannot permanently cement a galvanized steel pipe into a masonry wall. You can insert one into a thimble or crock that is permanently sealed to the face of the flue then make a removeable seal btw the pipe and the thimble flush with the inner face. Better yet, reline the chimney bringing the ss liner into the room a few inches and make your connection there.

A 9"x13" TC lined flue is probably grossly oversized. When the WH alone is firing it will probably backdraft. There is a 100% chance that TC lined flue would fail a Level II inspection, which it should undergo. That would bring you back to the liner. If you sweep a liner into the room, you can manifold the WH in with the boiler connector if properly sized and the vent rise off the appliance maximized while maintaining clearances to combustibles. Putting the WH above the boiler breaching is so it has the maximum vent rise. There is a lot of argument about interference from the bigger appliance blocking the little guy. I don't see that problem because I insist on a liner with manifold or I walk. I've never done the 3" WH connector above the boiler. I always test my installations including combustion analysis and a worst case depressurization test so I know it has the best chance of working under adverse venting conditions like summer time.

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1815247#Comment_1815247

And I defer to @Bob Harper on venting issues. So get your chimney inspected and perhaps have a stainless steel liner dropped into the clay liner, have it curve into the basement where you can attach to the appliance connector(s) with a properlu sized manifold. The liner will be sized to the connected appliances and may be as small as 5" diameter, so it will fit nicely in the clay tile liner.

Bottom line is that you do not want a down draft to force carbon monoxide (colorless/odorless) creeeping into your home when you are asleep. You don't want to wake up dead tomorrow!

PGB1

Thank You All for helping and explaining.

After reading what each of you wrote, having a liner(s) installed will move up on our "money eaters" list.

For the immediate, temporary repair I will follow the advice that you all shared as well as possible. Sealing the 3" to the inside face of the masonry is going to be interesting, but other than that I can follow the drawing that EdTheHeaterMan was kind enough to supply. There are sleeves for the connector pipes into the masonry, as Bob Harper mentioned.

At liner time, I will insist that the contractor have a Level II inspection done, as mentioned by Bob Harper.

Thanks EdTheHeaterMan for the corbon monoxide reminder. We've always been over-minimum on CO detectors. (And smoke/fire) I worked in a big city as a police officer before detectors were common. I found too many dead people from CO poisioning. (Usually gas space heaters in the house) It scared me wise.

There are two CO detectors in the basement- one adjacent to the boiler, water heater and clothes dryer. We have two on the first floor and one on the small second floor in the sleeping area.

And, it's very important to respect the expiration date on carbon monoxide, smoke and/or fire detectors regardless if the "test" button still works.

Paul

PGB1

Thanks Again everyone for helping and educating.

The new pipe will be temporary until we can get a liner and manifold professionally installed with permit. But, it may have to last through winter, depending on other $$ situations.

Out of curiosity, does the snap-lok seam on the horizontal (<1/4"/ft rise) go on top, on the side, on the bottom- or is it unimportant?

Thanks Again,

Paul

Bob Harper

There is no standard specifying where the seam must go. For practical reasons I teach keeping the seam out of 5-7 O'clock positions on horizontal runs (less than 45 degrees from level). You must have a minimum of 3 screws per joint equidistantly spaced. Again, keep the screws out of the 5-7 positions because the acidic flue gas condensate will eat up crummy electroplated screws. Even if you use ss screws the acid will attach the thin wall of the pipe at the hole where there is no zinc plating eating the hole larger and larger until the screw falls out. I've found many screws on the floor. Even though NFPA 31 calls for the male end up, this is one time I overtly defy a standard. EVERY listed venting system uses a male-down orientation to contain the condensate. It you have to hand crimp a joint and you're worried about flow disturbance just butter the joint with furnace cement for a smooth transition into the next section.

Listed CO alarms are death alarms only. They do not protect against low level CO. Get unlisted low level CO monitors.

HVACNUT

My chimney is interior. 9x9 terra cotta at the breach. My boiler flue is 7". I took a 26 ga. 9x7 squat reducer and crimped the 9 into the breach. Some steel wool at the corners, and retort cement.