Help Needed!! Type L-Vent as a Chimney Liner, but no masonry on roof (just a vent)?

Ramos1445

Hello,
I am the new Homeowner of a two-family house built in 1914. I have no experience in chimneys or venting, so I apologize if my explanation is not good or just bad questions, but I need some help. The house is two stories and split down the middle seperate basements and attic.

1. I am getting a new metal shingle roof installed. Roof is 25+ years old and needs it badly. I also want to do solar on the back side of the house (it's south-facing) and eventually turn the house into all-electric.

2. I have been looking at the chimney since I am doing a new roof. It is a pretty large chimney, about 6 ft tall. You can see it below.



The bad thing about such a big chimney is that it leaves a huge shadow on the roof and i want a clear roof for the solar. Also I would just like to have a consistent roof layer of shingles with minimal penetrations through the roof.


I currently have a 2019 oil Conforto KHM 100 by granby. Here is the manual https://granbyindustries.com/wp-content/uploads/2020/12/KHM-Oil-Manual-E2-Rev-I.pdf

From what I read the " Furnace is approved for factory built chimney type L vents. Breech is certified for 5” vent pipe."



Currently, the furnace is venting to the chimney.



This is a picture looking up from the opening.



When I looked online, I found this manual from Metal Fab. It states

https://mtlfab.com/media/L-Vent_Installation_Instructions-L2147.pdf

""Type L-Vent as a Chimney Liner"

"1. Type L-Vent may be used as a chimney liner in
an unoccupied masonry chimney. It may be used in
conjunction with stainless steel flexible liners or connectors
in chimneys with offsets"


Here are my questions:
1. Am i interpreting this right that I can use the existing chimney and then use L venting up to the top?

2. If so can I remove the chimney to the roofline and install a vent per the metal fab manual (below)? In other words remove the huge chimney and just use proper pipe venting.



The "why" behind this is the vent will have a much smaller impact on the solar, and with the chimney removed, the roof will be as continuous as possible until I turn the house into electric.

The end goals are to get a clean roof for solar, keep existing furnace for now until solar is installed, and then transition to electric.

Thanks

Jamie Hall

Well... I personally doubt that you will gain that much solar from getting rid of the chimney, and I assure you that getting a decent flashing job around the stove pipe will be every bit as difficult as getting one around the existing chimney. So i wouldn't consider it. But that's me.

There is another point, however. That Type L is OK -- so long as it is in the existing chimney. It is NOT ok if it isn't. At some point as you go up, you will have to change from that to double wall. Further, if that transition is within the attic, I'd be very concerned about it. Where you transition from lined masonry to unlined metal pipe is going to be a weak point -- and I for one would want that outside, rather than in the attic where I couldn't keep an eye on it. But again, that's me.

Ironman

L vent, like B vent for gas, can go directly through the roof. Proper clearances from combustible materials must be maintained (see manufacturer’s specs).

You better do a Manual J load calculation before you decide to switch to electric. It may not be sufficient in colder weather and the solar will probably only carry about 30% of it.

EdTheHeaterMan

I believe this is what you may want to do.


Since the L vent is approved for use as a liner in a vacant masonry chimney and you want to remove the masonry above the roof line, you could get the portion that extends thru the roof made out of Class A vent and use an approved connector form the L to the A portion that exits the roof.

Depending on the specifications of your oil fired appliance if the maximum temperature exceeds the L vent rating as a manufactured chimney, you need to use the L vent in the attic as a connector to the A Vent.

If your appliance has a specification of less than the maximum temperature then you can just use the L vent thru the roof with the manufacturer's recommended flashing and cap.

@Bob Harper is the guy who knows what will work and what is not going to work.

And I hate it when I go to the hardware store for something that I am going to use on my Model T Ford and the helpful hardware man tells me that what I'm looking for is not made for that.

Guess what.... Nothing in that store is made for a Model T Ford, but that didn't stop the dead guys that were around in 1908 from doing it anyway. So don't let anyone tell you not to remove your chimney 'cause it won't get you that much more solar. If you want to do it, and there is a safe way to do it, then just do it

EdTheHeaterMan

Further investigation: Your furnace is of a low enough exhaust temperature to use the L vent system thru the roof. You will not need the A vent for the section thru the roof. Just follow the manufacturer's instructions for the type L Vent to be safe. and the part about the stainless steel above the roof line is important... you don't want a huge rust spot on your new metal roof.

LRCCBJ

The photograph of the chimney shows that its total width is about four feet. This implies multiple flues in the chimney. Are there any fireplaces in the house on the same wall as the chimney? You would lose the capability to utilize them if this is the situation and you go forward with the chimney removal.

Ramos1445

Jamie Hall said:

Well... I personally doubt that you will gain that much solar from getting rid of the chimney, and I assure you that getting a decent flashing job around the stove pipe will be every bit as difficult as getting one around the existing chimney. So i wouldn't consider it. But that's me.

There is another point, however. That Type L is OK -- so long as it is in the existing chimney. It is NOT ok if it isn't. At some point as you go up, you will have to change from that to double wall. Further, if that transition is within the attic, I'd be very concerned about it. Where you transition from lined masonry to unlined metal pipe is going to be a weak point -- and I for one would want that outside, rather than in the attic where I couldn't keep an eye on it. But again, that's me.

Thank You! I totally hear you on the flashing, and for sure, I will not get much out of the solar. For me its more about cleaning the area up before the new roof.

One clarifying question. "That Type L is OK -- so long as it is in the existing chimney. It is NOT ok if it isn't. At some point as you go up, you will have to change from that to double wall." So the furnance vent just ends where the enters the chimney and does not run up it. So there is no L vent running up. I would have to install that.

Re: L vent going through the attic and home. Sorry for my ignorance here, but are L vents not double-walled? Sounds like they may be single-walled. So basically, I would have a single wall vent pipe going through the chimney (which would pass through the home attic included).

Not sure if there is double walled L vents pipes, if so could I just run that all the way up?

Ramos1445

Ironman: Re your comments great points sorry for some reason its not letting me reply back to you. Load test is a great idea!

Ramos1445

EdTheHeaterMan said:

I believe this is what you may want to do.


Since the L vent is approved for use as a liner in a vacant masonry chimney and you want to remove the masonry above the roof line, you could get the portion that extends thru the roof made out of Class A vent and use an approved connector form the L to the A portion that exits the roof.

Depending on the specifications of your oil fired appliance if the maximum temperature exceeds the L vent rating as a manufactured chimney, you need to use the L vent in the attic as a connector to the A Vent.

If your appliance has a specification of less than the maximum temperature then you can just use the L vent thru the roof with the manufacturer's recommended flashing and cap.

@Bob Harper is the guy who knows what will work and what is not going to work.

And I hate it when I go to the hardware store for something that I am going to use on my Model T Ford and the helpful hardware man tells me that what I'm looking for is not made for that.

Guess what.... Nothing in that store is made for a Model T Ford, but that didn't stop the dead guys that were around in 1908 from doing it anyway. So don't let anyone tell you not to remove your chimney 'cause it won't get you that much more solar. If you want to do it, and there is a safe way to do it, then just do it

Great find on this picture. Yes, this is exactly what I was thinking!

Ramos1445

EdTheHeaterMan said:

Further investigation: Your furnace is of a low enough exhaust temperature to use the L vent system thru the roof. You will not need the A vent for the section thru the roof. Just follow the manufacturer's instructions for the type L Vent to be safe. and the part about the stainless steel above the roof line is important... you don't want a huge rust spot on your new metal roof.

Yes totally agree! The difference between the shingles and the stainless will have to be flashed properly for sure. One thing to note on our roof. We have planks currently. The roofer is going to install plywood over top then underlayment then shingles so i hope flashing will be like on a new home if that makes sense.

Ramos1445

LRCCBJ said:

The photograph of the chimney shows that its total width is about four feet. This implies multiple flues in the chimney. Are there any fireplaces in the house on the same wall as the chimney? You would lose the capability to utilize them if this is the situation and you go forward with the chimney removal.

Yes! I believe the other side has the same setup. So i am suspecting multiple flues as well. So I will definitely be taking a look. The upstairs bedroom had an old fireplace, but the fireplaces have all been cemented so not in use anymore.

Ironman

L vent IS double wall just like B vent. The difference is that the inner pipe is SS to withstand the corrosive effects of burning fuel oil. The outer pipe can be SS or galvanized. I’d use the double SS above the roof line.

Bob Harper

L vent all the way- done.

Ramos1445

Ironman said:

L vent IS double wall just like B vent. The difference is that the inner pipe is SS to withstand the corrosive effects of burning fuel oil. The outer pipe can be SS or galvanized. I’d use the double SS above the roof line.

makes total sense...now i just have to find a L Vent in long runs and then the manufacturer's recommended flashing and cap like was mentioned above

Ramos1445

Bob Harper said:

L vent all the way- done.

agree if you all have any manufacturers would be great, im likley going to have to do this for both flues, which could be an issue if too close to one another.

Bob Harper

If there are two oil furnaces located within the same Combustion Appliance Zone(CAZ), and there is enough room to run a large enough L vent or just use Class A "all-fuel" chimney up and out manifolding the two together. If you cannot manifold them, you may have to run separate vents/ chimneys. I agree extend the vent high up so the acidic flue gases do not downwash and corrode your metal roof. Anything over 5feet above the roof must have extended roof brackets to support it. Too tall and you kill the draft.
Just so everyone understands that photo: the flue is oversized, the flue tiles are shot, the mortar joints are non-existent, and that galvy. connector would have to cemented flush to the inner wall provided it passes through a thimble or crock that is surrounded by a min. 12" solid masonry units. This is typical of heating flues and why they must be relined.

Ramos1445

**So I am thinking of removing the clay liner all together to be able to fit the L vent pipe.

Ramos1445

Bob Harper said:

If there are two oil furnaces located within the same Combustion Appliance Zone(CAZ), and there is enough room to run a large enough L vent or just use Class A "all-fuel" chimney up and out manifolding the two together. If you cannot manifold them, you may have to run separate vents/ chimneys. I agree extend the vent high up so the acidic flue gases do not downwash and corrode your metal roof. Anything over 5feet above the roof must have extended roof brackets to support it. Too tall and you kill the draft.
Just so everyone understands that photo: the flue is oversized, the flue tiles are shot, the mortar joints are non-existent, and that galvy. connector would have to cemented flush to the inner wall provided it passes through a thimble or crock that is surrounded by a min. 12" solid masonry units. This is typical of heating flues and why they must be relined.

Sorry not sure what happened to my response, but i am hearing 3 things.

1. If I can combine them, then I can run one line. I read in NFPA that they have to attach at different heights and then some shut-offs or something have to be installed.

2. Try to get a happy medium on the vent pipe over the roof high enough so it won't impact the roof but enough to get a draft.

3. **** The picture you referenced was that picture I had up the flue, right? In other words, the clay tiling needs to be replaced and the chimney cleaned out. So, I am thinking of removing the clay liner altogether to be able to fit the L vent pipe. In this case, i think per NFPA 31 would designate this as a "special venting system". So, in my mind, it would be an LVent (special venting system") that happens to be in an old chimney.

6.7 Special Venting Systems.
6.7.1 Type L Venting Systems.
6.7.1.1 Listed Type L venting systems shall be permitted to be used with appliances that are
listed as suitable for installation with Type L venting systems.
6.7.1.2 Type L venting systems shall be installed and used in accordance with their listings
and the manufacturers' instructions.
6.7.1.3 A Type L venting system shall be capable of producing the minimum draft
recommended by the manufacturer of the appliance.
6.7.1.4 The flue gas exit of a Type L venting system shall be at least 2 ft (0.6 m) above the
highest point where it passes through the roof of a building and at least 2 ft (0.6 m) higher
than any portion of a building within 10 ft (3 m) of such Type L venting system.