Chimney Liner Question

thesouth18

Hello, I'm putting in a wood stove with a 6" (cross sectional area 28.28") pipe connector and a max heat output of 47,000 btu/hr. My chimney liner is an oval that is 4x7" (cross sectional area of 21.9"). my chimney height is about 30 feet and the horizontal run to the stove is about 16". Is this going to be ok? The chimney guys are wanting to put a new, larger liner in. Thanks!

LS123

hello @thesouth18 wood stoves exhaust gas can be up in 700 - 800 F, depend on the stove. I would hire a licensed contractor who installs wood stoves and get a free estimate, including cost of parts, labor etc... depending on where you live, there are some strict building codes, inspections by town or city before you can use the stove. it might be worthwhile exploring more depending on capacity of your wood stove. sometimes some stoves require double insulated steel pipes 8 inch, some 6 inch... other than that I am not qualified to give any feedback.

EdTheHeaterMan

There are 2 possibilities.
#1 is that the Chimney Pro is correct with requiring a larger size. Remember, this is the guy that must come back if the system fails to operate properly. (like insufficient draft which results in smoking up your building) They must stand behind their workmanship and provide follow-up service, so they want to do it right the first time.
#2 is that they just want to make a sale on a new liner that is slightly larger without regard to the fact that your existing liner is adequate for such a small stove.

To determine if you have #1 or #2, I would get at least 2 more professional estimates for the job. especially if they are free estimates. Is the pro that is "waiting" for the larger liner also the same pro that is providing the price for the new liner?

My expertise is with Gas-fired and oil-fired automatic heating appliances. we have specific flue sizing charts for each type of fuel (different for gas v. oil) and I believe that solid fuel appliances have another sizing table based on the different fuels used therein. NFPA publishes these tables for most of those applications. NFPA 54 is for Gas NFPA 31 is for Oil but I do not know which number is for Solid Fuel appliances. perhaps NFPA 211 may be the proper reference.

You will need to do more research. I hope this info helps a little.

EdTheHeaterMan

After further research, the NFPA 211 (https://www.cityofmtcarmel.com/sites/default/files/fileattachments/planning/page/7867/211-19-pdf.pdf) reads as follows:

4.1.1.2 The venting system shall satisfy the draft requirements
of the connected appliance(s) in accordance with the manufac‐
turers' instructions or approved methods.

7.1.11.1 Masonry chimneys serving appliances shall be sized
and configured in accordance with the appliance manufactur‐
er’s instructions, 13.4.4, or approved methods

This appears to be the only sizing criteria. SO...... What do the appliance instructions recommend for the liner size?

OR you can go to the ASHRAE design guidelines. That is where the manufacturers get their information when designing appliances.

thesouth18

Thanks guys.  So the company doesn’t just want to put a new liner in they want to rebuild the entire chimney because the current liner is stuck in there and to top it off, I just had it rebuilt back in October from the roof up.  Second that liner supported a huge wood stove for about 30 years (1970s-2000) that burns much hotter than the one I’m putting in so I feel good about that.  The current stove manufacturer states 6” pipe and the oval one would be the equivalent to 5.5”.  

I have had all sorts of issues with chimney pros here.  When had 6 different ones come out and we were told 5 different things.  One said there was no liner and it needed one, one that it had a clay liner and needed a stainless one, one that it had a stainless one but it wasn’t in good shape, and that’s just liner; I haven’t even talked about the masonry opinions...so I decided to look into myself.  

pecmsg

Manufacturer says 6” and you have 5 1/2. So it’s No Go!

Bob Harper

Some mfrs. will approve of a 5.5" liner if over a certain height (approx 30 ft.). We do it all the time without problems. The problem with a 4"x7" liner is insulation. Is this liner wrapped with 1/2" foil-backed ceramic fiber insulation for a zero clearance to combustibles 2,100F rating per the UL 1777 listing? If this is going into a nominal 9"x13" terra cotta tile liner, it might have room for the blanket if the tiles aren't staggered. That's one reason you must perform an NFPA 211 level II inspection prior to relining. Is this an interior or exterior chimney? What is the make and model of the stove?

thesouth18

https://www.woodstove.com/index.php/fireview  Here is a link to the stove.  The chimney is at least 30 feet high.  The liner is not insulated, it’s solid stainless steel.  It was built in 1886 so no taracotta tiles, just brick. It is an interior chimney up to the roof and extends 6 feet above the roof line.

Bob Harper

Chimney Flue Sizing:
The Model 205 Fireview Wood Stove has a 6” flue collar and a 6” chimney is considered
ideal. If upsizing needs to occur due to an existing chimney the following general rules
apply:
1. Interior Chimney (no walls of the chimney exposed to the outside below the roofline):
the inside cross-sectional area of your chimney should be no more than 3x the crosssectional area of the woodstove flue collar.
2. Exterior Chimney (if there are one or more walls exposed to the outside below the
roofline) - The flue should be no more than 2x the cross-sectional area of the flue collar.
Recommendation: Woodstock Soapstone recommends, for the Fireview wood stoves, a
maximum of 8 inch x 10 inch rectangular or 10 inch round flue tile for an inside chimney.
For an outside chimney, an 8 inch x 8 inch square or 8 inch round would be the largest
recommended. The smallest size we recommend is 6 inches round. DO NOT VENT THE
FIREVIEW INTO A CHIMNEY OF LESS THAN 6 INCHES IN DIAMETER.
Note: For flues that exceed the recommended area, a stainless steel chimney liner is recommended.
Height Requirements:
The chimney must extend 3 ft. above the point where it passes through the roof and
must also be 2 ft. higher than any roof surface or obstruction within 10 feet (measured
horizontally) of the chimney. You should check your local building codes for any other
requirements.
The recommended minimum chimney height is 15 feet from the flue collar of the stove to the top of the chimney. This
includes connector pipe and chimney pipe. There may be other factors to conform to code for clearances on the roof,
high wind, high altitude, etc., that may make the minimum height undesirable or a violation of building codes.
They provide their tech services number if you have questions about the venting. You must insulate the liner because you will not have the requisite 2" clearance to combustibles all the way through the house. It just doesn't exist in the wild. If you call tech svcs. and they tell you it's ok to use a 5.5" liner at that height, request they state it in an email.
Soapstone stoves are awesome because they have such a high specific heat meaning they can absorb and store lots of energy then release it slowly over time.

Coaly

Reducing vent diameter is no longer legal for a new install in most of the US and Canada for many reasons.

NFPA 211 allows 1 inch diameter reduction in size. However, most states have now adopted the International Family of Codes. This adopts NFPA 211 and adds NO reduction in vent size smaller than stove outlet is permitted. This is found in the International Mechanical Code for venting of solid fuel appliances. (NFPA 211 also has a section for installing unlisted appliances, but the International Code requires all appliances being installed to be UL Approved).

Any chimney not complying 100% with the current building code requires an insulated liner. Some requirements are a lined flue, including 2 inches clearance to framing for interior chimneys and 1 inch clearance for exterior chimneys requires an insulated liner. Most existing chimneys do not comply with this clearance.

And finally, all appliances must be installed as per installation instructions, most specifying a minimum and maximum diameter flue.

This is not always safety related or due to a physical necessity. An example is since most test with a 15 foot chimney, that is the minimum height required to be "installed as tested".

A good source for chimney pros is the Hearth.com Forum where you'll find me as coaly as well.