Furnace vents into chimney

[Matt Fellman]

When did it become dis-allowed to vent a furance and/or water heater directly into a chimney - Or, is it ever totally dis-allowed?

I ran across a permitted 2003 installation today of an 80% furance/water heater venting into a clay lined masonry chimney. I've never seen one that recent not being lined up to the top so it got me thinking. I thought anything after the mid 1990's or so was required to be lined.

Any thoughts?

[Darren Miller]

Matt;

It depends on several conditions.

If the chimney is an 'exterior' chimney, it has to be re-lined.
If it's an interior chimeny, it may have to be re-lined.

Here's some interesting reading:

Column - Plumbing and Mechanical (http://www.pmmag.com/Articles/Column/22094097850d7010VgnVCM100000f932a8c0____)


Column - Plumbing and Mechanical (http://www.pmmag.com/Articles/Column/e1434097850d7010VgnVCM100000f932a8c0____)

[Matt Fellman]

Good articles... thanks!

[Michael Thomas]

As I understand it, per my notes from various sources:

1) Currently, venting gas appliances to an unlined masonry chimney is prohibited.

2) Currently, venting gas appliances to a tile-lined masonry chimney is allowed if ALL these conditions as regards the chimney, are met:

- Allowed by local code

- All four walls of the chimney are within the building structure OR all requirements in chapter 10 and table 10 of the NFPA 54 are met.

- The liner is properly sized

- The chimney is constructed in accordance with the NFPA 211.

At least around here, the chances of all four of these being the case - especially in an older house - is about nil.

(Of course, the venting TO the chimney needs to be correct as well.)

Hopefully, Bob Harper or someone else will be along to flesh that out and/or correct me if I'm in error.

[H.G. Watson, Sr.]

Chapter numbering in NFPA 54 has taken a lot of changes with the last few editions, more helpful to metion the edition when it comes to NFPA 54.

You may view several recent additions on line at no cost. You have to register/sigh-up on the web site to view. You can register as an "other" type member for free, just activate the email generated from the sign-up process, then sign in.

Here is the link:

NFPA 54: National Fuel Gas Code (http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=54)

Scroll down below the description and see the portion titled in red "Addtional Information About This Document", see the links in blue referencing "View the XXXX edition of this document" and select one of the links. Pop-ups and java must be enabled to do so. Be patient first time viewing for the reader to load which will inturn generate a third window which will be the code document, a navigation tool (linkable table of contents) will be at the bottom right of the document and generates a fourth overlay window.

Here is a link to 211 also:

NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances (http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=211)

Most natural gas fired heating appliances reference NFPA 54 a/k/a National Fuel Gas Code in their instructions. NFPA 54 addresses connection to chimney.

Hope that helps.

H.G.

EDIT TO ADD:

P.S. It is most important to determine if the chimney is serving anything else.

If the appliances are oil-fired different rules apply. Oil-fired and gas-fired appliances should not share venting or chimney.

[Bob Harper]

H.G., the IRC has largely replaced NFPA 54 in most of the country. Since whatever code is the law, that and not some national std. is what would be enforceable. Nationally recognized stds. would be recognized by a court in the absence of an enforceable code (law).More and more mfrs. will begin to correct their manuals as they make other changes in them, which, btw, must be approved by the listing agency.

I recommend everyone get a current copy of the applicable codes in their area. Documents like NFPA 211, 54, and 58 still hold value but more for general reference and enforcement.
HTH,

[H.G. Watson, Sr.]

The aforementioned NFPA "codes" have been accepted as "Standards". Unlike the I-codes. This is why the manufacturers mention them in their instructions.

If the Standard is referenced and incorporated into the instructions......

[H.G. Watson, Sr.]

.....the most restrictive condition/circumstance/specification/limitation (s) apply/applies. ;)

[Jerry Peck]

... as well as ALL LOCAL CODES as all manufacturer's installation instructions will have wording similar to " ... and all local codes", with some even saying " ... and all local codes and ordinances" or wording to that affect.

Thus, the manufacturer's installation instructions *are code* by reference, and, being as NFPA 54 and other standards are referenced in the manufacturer's installation instructions, all such referenced standards *are code* too, with both code and manufacturer's installation instructions saying to install/use/whatever in accordance with ... the manufacturer's installation instructions and the codes.

The code states that where there is a conflict between a general requirement and a specific requirement the specific requirement shall take precedence (whether or not it is more restrictive), and when there is a conflict between requirements the most restrictive shall apply, meaning such as a conflict between two general requirements, two specific requirements, etc., as the code has specifically deferred from general requirements to specific requirements.

Additionally, some code sections state that if there is a conflict between the manufacturer's installation instructions and the code, the code shall govern *provided that* the code does not violate the listing, labeling, and installation instructions, i.e, if the code is more stringent, the code shall govern even though the code had deferred to the manufacturer's installation instructions.

[John Dirks Jr]

Is it sharing the chimney with a fireplace? Did I miss that somewhere? If it's not sharing the flue, what's the big deal?

[Michael Thomas]

Flue used by a 105K BTU CAT I furnace and a 40K BTU gas water heater, interior chimney.

Sizing issues aside, is this degree of tile misalignment likely a significant tissue?

[Bob Harper]

Michael, of course nobody can perform a full Level II based upon photos on the web. However, a few simple points:
The chimney must be suitable for the class of service. Is it?
Can this flue maintain its integrity the full length? Any missing mortar or gaps?
Sizing would probably require a 5 or 5.5" listed liner.


Sorry HG but you are allowed to common vent gas an oil as long as there is suffiicient vent capacity and both appliances have primary safety controls.
Bob