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Short  metal chimney (C) Daniel Friedman Installation & Inspection of Type L Chimneys
& Type E Vents for Oil Fired Appliances

L-vent chimney specifications:

This article describes the installation and inspection of L-Vent chimneys used to vent oil-fired heating systems. We illustrate both safe and unsafe L-vent metal chimney installations, including chimneys that are too short, too close to other structures, are damaged, or are missing components.

Our page top photo shows an L-vent chimney that is too short above the roof, and too short in total rise - the oil fired boiler it vents never worked properly and always had marginal draft until this chimney was replaced with a taller unit.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Type L Vents - Double Wall Metal Vents

Type L Vent (C) Carson Dunlop AssociatesWe use Type L-Vents, double-walled metal chimneys for venting heating appliances not only for fire safety but also because the insulation provided by the doubled walls improves draft - an important safety requirement when venting oil or gas fired appliances.

A Type-L vent is used for oil-fired appliances but can also be used for venting natural gas fired appliances.

But as we explain at TYPE B VENT vs L VENT DIFFERENCES, the reverse is not true - that is, you can substitute an L-vent chimney for a B-type vent, but you cannot go the other way: a B-type vent chimney cannot be used in high temperature applications where an L-vent chimney is required.

As Carson Dunlop Associates' [reference] sketch indicates, Type-L vents are tested to 1000 degF.

Some products list lower listing temperatures, as we explain here.

Some manufacturers such as Metal-Fab, Inc. provide installation manuals for L-Vents indicating that their L-Vent systems are listed for gas and oil furnaces that do not exceed 570 degF at the outlet temperature [of the furnace or boiler], and for 1700 degF. for a 10-minute "safety overfire" situation."

In the U.S. in the 1940s - 1960s, Type E vents, such as Condensing Engineering's Vitroliner were UL listed for use with multiple fuels such as gas and oil, and are in our opinon a predecessor of modern L-vent chimneys. See details at

TYPE E VITROLINER CHIMNEYS

L vent and B vent height requirements (C) Carson Dunlop Associates

Chimney Height Requirements for Type L Vents

Short  metal chimney (C) Daniel FriedmanHeights for both L-Vent and B-Vent metal chimney vents are shown in Carson Dunlop Associates [at REVIEWERS] sketch. You will see that the L-Vent needs to be at least two feet above anything within ten feet of the chimney, and it should be at least two feet above the roof surface.

The sketch notes add that a metal chimney venting a wood burning appliance like a woodstove must be at least three feet above the roof surface.

Here is a metal chimney which is obviously too-short, violating both of the height specifications cited just above. The chimney is less than two feet above the ridge and less than three feet above the roof surface.

You may also notice that it was improperly installed - the roof flashing sides are open to leaks.

More complete details about chimney height requirements on buildings is

at CHIMNEY HEIGHT & CLEARANCE CODE

L-Vent Chimney Fire Clearance Details

More complete Details about L-Vent chimney fire clearances indoors can be read

at FIRE CLEARANCES, METAL CHIMNEYS.

L-Vent Type Chimney Defects, Goofs, and SNAFUs

In addition to the "too short" L-vent type chimneys already describe above, here are some other troubles to look for.

How about that rusty L-type chimney at below left?

Type L chimney defects and hazards (C) Daniel Friedman Type L chimney defects and hazards (C) Daniel Friedman

At above right the metal cap has rusted and blown off of this Type L vent serving an oil fired heating system. Rain down the flue invites corrosion, chimney damage, and unsafe flue, and a damaged heating appliance.

In my photo below we can see stains showing that water has been running down inside this chimney, leaking out inside the building. In some installations, depending on how the flue vent connector joins the chimney, water runs on into the heater itself.

Type L chimney defects and hazards (C) Daniel Friedman

This article series on chimneys, chimney construction, and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects.

Type E Vents: the Vitroliner Insulated Chimney

Vitroliner Type E insluated chimney in a 1948 brochure from the manufacturer, Condensing Engineering, cited and discussed at InspectApedia.com

A predecessor to modern L-vent chimneys were E-vents, [shown above] an insulated metal (and other materials) chimney flue listed in the U.S. by Underwriters Laboratories as suitable for multiple fuels, such as the venting of natural gas and oil in the same chimney.

Watch out: nevertheless there are fue venting and fire hazards if you combining a wood burning appliance or some other solid fuel burning appliances with gas and/or oil fuel combustion gases into the same flue.

Photso below of a Vitroliner Type E chimney top and of a Vitroliner's UL label, provided courtesy of home inspector Lawrence Transue who found this Virtoliner type E chinney in a Pennsylvania home constructed in 1957.

Metal chiney top over a Vitroliner Type E insulated chimney on a 1960's Pennsylvania home (C) InspectApedia.com Transue

Watch out: in our OPINION, considering that the chimney is now 60 years old, even though it was a listed (approved) product at the time of original manufacture and installation, it would make sense to inspect the flue interior for signs of damage or corrosion.
That rust at the chimney top is typical and doesn't address the flue itself. Hidden from us are the condition of the chimney's interior surface, its insulation, and also the condition of the chimney's aluminum liner layer that in our OPINION is not necessarily very-long-term durable if exposed to corrosives from a combination of flue product deposits and condensation or leaks.

Really? An abundance of caution is appropriate where fire and life-safety questions pertain, but old doesn't necessarily mean "no-good" (the InspectApedia.com editor is ... old.)

In follow-up Mr. Transue reports:

The home buyer hired a chimney inspector who found that this chimney was is in nice shape. Just had a new furnace in 2016.

 

Vitroliner Type E chimney UL label on a 1960s home (C) InspectApedia.com Transue

Type E Vent Chimneys and Vitroliner Type E Research

Special thank you to:

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question:

(Nov 26, 2012) Ric said:
I have changed from an old Anthes furnace from 1970s to mid efficiency 60K BTU gas furnace. The furnace guy says that because it is less than 80K BTU therefore it needs a Type B venting. This does not make sense, as Type B has lower resistance to temperature than Type L.

Thus having Type L is more safe just in case there is overfiring etc. I suspect this guy is trying to make money in addition.

Also, the old furnace has a gas connection where the gas pipe coming down vertically has slight bent like 5 degrees max. This has been since I bought the house.

He says this bent is not right and needs a modified gas connection. Pls. advise what should I do regarding these issues. Also, previous gas connection had a street elbow instead of a regular one and he says street elbows are not allowed.

Reply:

Ric I think you're right that as long as the size dimensions & clearances are correct you can use a safer, better-insulated type chimney. Did you ask your local building department what they'll approve?

I'm not sure what to make of the bend in your gas piping, but I do warn that any gas leak is of course very dangerous, risking an explosion, fire or other hazards. Ask your licensed plumber to take a look.


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