chimthik.txt -> aschim02.txt ---------------------------------------------------------------------------------------------------------- NOTICE: (C) Inspectapedia.com, readers interessted in this text should see UNLINED FLUE INSPECTIONS at https://InspectAPedia.com/chimneys/Un-Lined_Chimney_Flues.php Also see our chimney home page at CHIMNEY INSPECTION DIAGNOSIS REPAIR URL: https://InspectAPedia.com/chimneys/Chimney_Inspection_Repair.php --------------------------------------------------------------------------------------------------------- Chimneys Unlined Flues Thickness of masonry required Summary: In Canada, single wythe brick flues are accepted In many US locales single wythe brick flues are in use; however several standards require or recommend either re-lining (and other safety measures) or the confirmation that 8" of solid masonry exists - ie a double wythe or greater flue. Details: TO: Al Carson re MASONRY CHIMNEY - single wythe vs 8" masonry unlined flues I've sent to you by mail today hard cc of HR Book changes with a *few* annotations - most will follow later. Chimney refs from Doug Hansen are included. The "requirement" for 8" of solid masonry OR for use of a flue liner was listed in the One and Two Family Dwelling Code for New York, in 1979, in Chapter 9, Chimneys and Fireplaces, New York 1979 Code: Para R-906 - Flue Lining (Material) Masonry chimneys shall be lined with fireclay flue liners not less than 5/8 of an inch in thickness or with other approved liner material that will resist, without cracking or softening, a temperature of 1800 deg. [F] Exception: Masonry chimneys may be constructed without flue liners when walls are at least 8" in thickness. This requirement was dropped when New York changed from an explicit specification code to a [stupid] "performance" code in January 1984. - New York 1984 Uniform Fire Prevention and Building Code, Article 10, Heating, Ventilating, and Air Conditioning Requirements 1000.2h-1 Equipment for burning solids or liquid fuel shall be connected to suitable chimneys or flues, or vented as set forth in 1000.2h-4 and shall not be connected to gas vents. .2h4 addresses direct-venting equipment 1005 Chimneys and Gasvents 1005.1a Masonry and factory-built. Chimneys, gasvents and their supports shall be designed and constructed so as to be structurally safe, durable, smoketight, noncombustible, and capable of withstanding the action of flue gases without softening, cracking, corroding or spalling. .../ 1005.1d Flue linings shall be capable of withstanding the action of flue gas without softening, cracking, corroding or spalling at the temperature to which they shall be subjected. Other paragraphs bring up the requirement that no adjacent materials can be heated (by the chim/vent) higher than 175 degF. [Surely in concern for pyrolysis.) Al since the state backed off of quantitative code, many inspectors continue to require something explicit, particularly when examining older building to which older codes pertained - and I am probably not the only one who keeps two older generations of code manuals around as "interpretation" aides for the current more vague writing. Uniform Mechanical Code - UMC 1991 Sec 913 (a.) Masonry Chimneys - refers to Chapters 23, 29, and 37 of the Building Code. - Gas venting into existing masonry chimneys. Existing lined masonry chimneys and unlined chimneys with not more than one side exposed to the outside may be used to vent gas appliances provided: 1. An approved liner shall be installed in an existing unlined masonry chimney when deemed necessary by the building official considering local problems of vent gas condensate 2. The effective cross sectional area is not more than four times the cross sectional area of the vent and chimney connectors entering the chimney 3. The effective area of the chimney when connected to more than one appliance shall be not less than the area of the largest vent or chimney connector plus 50% of the area of the additional vent or chimney connectors [This is identical to my detailed flyer and sketches I obtained from Beckett Corp on this issue.] There are other restrictions, getting a bit afield here, except for requiring checkout for blockage, cleaning old creosote, providing cleanout or capped tee, etc. Unlined chimneys with more than one exposed side (outside) have to be lined per this paragraph. The UMC has nice details and tables on what devices can be vented through what types of chimneys, clearances, shared flues, etc. They don't address (far as I can see) masonry thickness questions, except as follows Table No. 9-D--Chimney Connector Systems and clearances from room wall combustibles for residential heating appliances System A, 12" clearance - A 3 1/2" brick wall shall be framed into the combustible wall. A 5/8" thick fire clay liner shall be firmly cemented in the center of the brick wall maintaining a 12" clearance to combustibles. The clay liner shall run from the outer surface of the bricks to the inner surface of the chimney liner, but it shall not protrude into the chimney liner. The above was not changed by amendments as of 1993. This, of course, is discussing thimbles, not flues. We need to take a look at Building Code 23 29 and 37 - which I don't have - Douglas might, or perhaps you do. In addition, Doug Hansen refers us to NFPA 211: Chimneys, fireplaces, vents, & Solid fuel burning appliances - I don't have but am ordering this reference from NFPA 800-344-3555 Item LT-211-92 $18.75. Doug also refers to "Residential Masonry Fireplaces and Chimney Handbook" which I've seen (borrowed cc) and which is on our exam reading list. This in turn references ASTM C-315 in the section on flue construction. [Thanks to Douglas for these references.] Summarizing our discussion of risks to clients, I agree that oil and solid fuels are probably more risky of fire than gas - for the obvious reasons of operating flue temperatures and combustible flue deposits. Gas in turn seems to do more damage to old soft bricks - precisely what were used in single-wythe old unlined flues. OTOH, if there's an opening in the old flue the risk of venting CO into the house (excepting blocked flues) is probably less than the risk of reduced draft due to infiltration *in* to t he leaky chimney. In my now infamous Port Jervis case, the entire flue was totally blocked in the basement, and the gas-fired boiler was venting all into the basement area, sending water streaming down masonry walls - the owner thought there was a water entry problem from wet soils. Single wythe flue, bricks fell down from in the attic near the top of the chimney; roof deck in the attic had been charred, probably by prior appliances, but was no longer in danger as the chimney now vented directly into the basement! Where states such as NY have gone to a performance code we are probably jeopardizing our clients if we are not aware of what some reasonable benchmarks are for acceptable chimneys, and if we don't make people aware of telltale signs and conditions in which further investigation is warranted. I'm placing this note in our upcoming Reference Lib under HEATING - and so will add/correct/update it as suggested by reviewers. Dan Friedman 10/29/93 03:38 PM cc: Doug Hansen References added per note from Bob Klewitz 11:46PM 10/30/93 Wood Heat Safety, Jay W. Shelton, Garden Way Publishing, Charlotte VT "Chimneys, Fireplaces, Vents, and Solid Fuel Burning Appliances," NFPA "Solid Fuel Encyclopedia," Wood Heating Alliance, 1101 Connecticut Ave N.W., Suite 700, Washington DC 20036 202-857-1181 Bob K's note included no citations regarding basis for requiring 8" solid masonry where lined flues not installed. CHIMTHIK.TXT 11:50PM 10/30/93