if ; Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

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* on October 9, 2015.

NATIONAL BUREAU OF STANDARDS REPORT

75ao

LITERATURE AND INFORMATION SURVEY

ON

CHIMNEYS AND FIREPLACES

By

H. Shoub

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent

with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials, devices, and structures; advisory services to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications. The work includes basic

and applied research, development, engineering, instrumentation, testing, evaluation, calibration services,

and various consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau's

unique competence is required. The scope of activities is suggested by the listing of divisions and sections on the inside of the back cover.

Publications

The results of the Bureau’s research are published either in the Bureau’s own series of publications or

in the journals of professional and scientific societies. The Bureau itself publishes three periodicals avail- able from the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary and pre- liminary reports on work in progress; and Basic Radio Propagation Predictions provides data for determining

the best frequencies to use for radio communications throughout the world. There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks, Miscellaneous Publications,

and Technical Notes. A complete listing of the Bureau’s publications can be found in National Bureau of Standards Circular

460, Publications of the National Bureau of Standards, 1901 to June 1947 (SI. 25), and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957 ($1.50), and Miscellaneous Publication 240,

July 1957 to June 1960 (Includes Titles of Papers Published in Outside Journals 1950 to 1959) ($2.25); avail- able from the Superintendent of Documents, Government Printing Office, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1002-30-10627 May 31 , 1962 7520

Literature and Information Survey

on

Chimneys and Fireplaces

by

H. Shoub

for

Federal Housing Administration

IMPORTANT NOTICE

NATIONAL BUREAU OF STANDARDS REPORTS are usually preliminary or progress accounting documents

Intended for use within the Government. Before material in the reports is formally published it is subjected

to additional evaluation and review. For this reason, the publication, reprinting, reproduction, or open-literature

listing of this Report, either in whole or In part, Is not authorized unless permission is obtained in writing from

the Office of the Director, National Bureau of Standards, Washington 25, D. C. Such permission is not needed,

however, by the Government agency for which the Report has been specifically prepared if that agency wishes

to reproduce additional copies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Literature and Information Survey

on

Chimneys and Fireplaces

by

H. Shoub

ABSTRACT

To secure information relevant to questions

that have been raised concerning the adequacy or

correctness of the requirements for the construction of chimneys and fire places in the Federal

Housing Administration Minimum Property Standards,

a search was made of pertinent literature available

at the National Bureau of Standards.. In addition

to a review of this material, a further bibliography

of papers of interest was prepared. To the extent

possible, answers with cited references were supplied

for the points raised. It was suggested that while

research data were not in every case available,

practical experience could be a source of supplemental

knowledge

.

1. Introduction

The Federal Housing Administration Minimum Property

Standards for One and Two Living Units (FHA No. 300) were

considered to have inconsistencies and omissions in the require

ments for fireplaces and chimneys, arising from a basic lack of

knowledge of the factors affecting their fire safety.

FHA Proposal 1.26 (Appendix A) was formulated to identify

some 18 areas in which more specific information on the design

and construction of fireplaces and chimneys was needed. As a preliminary to possible further work or technical investigation

it was decided that a literature survey of published and unpublished data available at the National Bureau of Standards

might prove fruitful in providing answers to at least some of

the questions posed in the FHA proposal.
2

In addition to examining the material in the Bureau's

Fire Research Section, a bibliographic study was undertaken..

Reference was found to several very early works on fireplaces

and chimneys. Three of these were of considerable significance,

the earliest being that of M. Gauger, "La Mecanique du Feu,"

published in France in 1709 (an English translation was ma.de

by J. T. Desaguliers in 1715)* Benjamin Franklin's contribution

to the science of domestic heating appeared in 1745 with the

publication of his "Papers on Philosophical Subjects." A

remarkable work was Count Rumford's "Chimney Fireplaces"'( 1796) . The result of scientific investigation, it contains rules for

the construction of fireplaces that are valid and in use today.

Indeed, it may be the basis of some of the "conclusions based

on long experience" often found in papers relating to heating

problems

.

The bibliography of works on chimneys and fireplaces' is

presented in two sections, the first containing those papers

available for review, for which a brief summary or indication

of the contents is given, the other listing works which, while

possibly having some information of interest, were not obtainTM

able within the scope of the program outlined to FHA. Being

closely associated, papers on both chimneys and fireplaces are

presented together.

2. Bibliography of Papers Available for Review at NBS

1. Chimney Design and Theory, by Wm. Wallace Christie,

Van Nostrand 1902: One chapter on residential chimneys;

formulas for area of chimney flue as a function of size

of grate in coal-burning stoves.

2. Thermal Insulation and Fire Protection of Small Chimneys,

by Paul Becher, Ingeni^ren(Copenhagen) Vol. 64, No. 42,

1955, pp. 827-31 : Chimneys of various masonry constructions, times of curing, flue diameters, outer protections;

fuels anthracite, coke, lignite, peat, wood, oil, city

gas; examples of good and bad practice in chimney design,

heat transmission data.

3 . Tests on Types of Chimneys with Regard to Fire Resistance,

by Gerhard Hansen, Ingeni^ren( Copenhagen) Vol. 64, No. 42,

1955, pp. 832 -33 : Light-weight concretes (pumice, cinder,

etc.) tested to 1000°C; small heating stove source;

describes development of dangerous cracks; brick chimney

reference.
- 3

-

4- The Construction of Central Heating Flues, by M. Bergstrom,

Teknisk Tidskrift (Stockholm), 80 ( 13 ), 1950, pp. 288-94:

Temperatures in soot fires to 1300°C; tests of chimneys

having inner and outer shells of brickwork with intermediate

layer of mineral wool; also outer layer of concrete approximately 4-in. thick; states that inner lining should be able

to move freely when expanded by heat; minor cracking of

inner shell not important if outer shell remains intact.

5. The Problem of the Flue from the Fireman’s Point of View,

by I. Stromdahl, Teknisk Tidskrift, 80 (

1

3 ) , 1950,

pp. 283 - 6 : Temperature rise in flue fires may be very

rapid (in one test 900°C in 3 min, 1300°C in 15 min) ; wood

supplanted coke as fuel.

6. Fires in Flues from the Point of View of Insurance Companies,

by A. Sylven, Teknisk Tidskrift 8Q ( 13 ), 1950, pp. 286-8:

Quick fires of short duration seldom cause damage to a wellconstructed brick chimney, even at very high temperatures;

inner brickwork of double-shelled brick chimney with mineral

wool between withstood 10 soot fires to as high as l400°C

before destruction.

7. Recommended Minimum Requirements for Small Dwelling Construction, Bureau of Standards Building and Housing

Publication No. 18, 1932, pp. 19-22 and 79-89 : Designs of

chimneys and fireplaces, and ^methods of framing combustible

members around them (mostly from NBFU) ; recommends round

flues as providing better draft; ceramic flue lining, not

parged brickwork; states that various studies indicate that

the minimum height of chimneys for dwellings should be 30 to

35 - f t

'

’ chimneys less than 30 ft are apt to be erratic in

behavior; for fireplaces, good draft design requires

an effective area of flue of 1/12 of the area of the fireplace opening.

8. The Problem of the Open Fire, by W. F„ B. Shaw, J. Institute

of Heating and Ventilating Engineers, Vol. 23 , Sept. 1955,

pp. 205-28: Review of open fire (coal or coke) heating;

problem of excess air flow - recommends 4-in. wide chimney

throat (based on work of Rumford, 1796)

.
9 .

- 4 -

Temperature of the Wall Behind a Back-Boiler Fire, by

L. L. Fox and D. Whittaker, J. Institute of Heating and

Ventilating Engineers, Vol. 26, 195^8 , pp. 80-5 : Model

byelaws state that thickness of the rear wall of the

fireplace recess shall be not less than 4 in. for external

walls or 8-1/2 in. for internal. On a bare 9-in. brick

back wall, the highest temperature on outside surface was

130°F with coke fuel and 150°F with coal. Burning house coal

at the greatest possible rate for 12 hours, a boiler fire

produced a temperature of 175°F on a bare outside wall

9 inches thick, and 305°F on a 4-1/2 thick wall. With a 1-in. board cemented to the brick, temperatures of 265°

and 570°F were attained on the brick for the two wall

thicknesses

.

10. Influence of Air Flow on Intermittent Heating with the Open

Fire, by L. L. Fox and D. Whittaker, J. Institute of Heatijig

and Ventilating Engineers, Vol. 26, 1958, pp. 221-31*

Open fire performance related to chimney air flow and the

heat capacity of a massive chimney-breast . Improvement

of efficiency results from a reduction in chimney air flow.

11. Some. Measurement of Temperatures of Metal Flues of Domestic

Heating Appliances, by L. L. Fox and D. Whittaker, J. Institute of Heating and Ventilating Engineers, Vol. 23, 1955,

pp. 183-92: Three types of small solid-fuel appliances in

normal operation; gives temperatures of flue gas and surface of sheet metal flue pipe; coal and coke fuels-coal

gave higher flue gas temperatures; states that in a closed

fire with solid fuel, considerable and rapid changes in

temperature are possible; some mention of fire hazard to

adjacent timber (no data)

.

12. An Analysis of Survey Information on Chimney Fires, Join,t

Fire Research Organization (UK), May 1957: Ho evidence

that use of fuels other than coal contributed substantially

to the incidence of chimney fires (except for some coke,

fuels other than coal are little used in Britain) ; suggests

that frequent cleaning of lower part of the chimney may be

an important factor in preventing fires.

13. Chimney Flues of Concrete Block, Centre Scientifique et

Technique du Batiment (France), No. 44, Cahier 3^8, June

I960: Lightweight concrete chimney block units, some with

coverings of 1 or 2 cm of plaster; temperatures on interior

and exterior faces of flue for various flue gas temperatures;

fuels were coal, wood, oil; effect of heat on various concretes.
- 5 -

14. Station for Tests^of Chimney Flues, Centre Scientifique

et Technique du Batiment (France), No. 47, Cahier 379,

December I960, p. 14* Tests for the effect of thermal

shock (flue gases at 9-00° and 500°C) on concrete block

chimney flues; gas permeability (before and after

thermal shock) of the blocks.

15. Contribution to the Study of the Behavior Under Heat of

Concretes for Chimney Flues, by M. L. Boy, Centre

Scientifique et Technique du Batiment (France), No. 51,

Cahier 408, August 1961: Description of concretes

offering resistance to heat effects and thermal shocks,

for use in chimney flues; concludes that concrete flue

liners should not be subjected to thermal shock until

several months after fabrication; currently used cements

(in France) behave much the same under heat, but it is

necessary to choose an aggregate with a low coefficient

of expansion; temperature gradients in chimney walls are

great enough to engender high thermal stresses.

16. Flues (Approval of New Materials and Non-traditional

Methods of Construction), Cahiers du C.S.T.B. (France)

No. 49, F. 4 1961, 392: Approval tests on various proprietary 'concrete chimney flue blocks, mainly with pozzualanic

aggregate; description of cracking from thermal shock,

and transmission of flue gases through block.

17. Testing of a Chimney, by Gote Larsson, Statens Provningsanstalt, Stockholm, Meddelande 125, 1959 : Many fires

originate in chimneys; tests with brick chimneys indicate

that with a wall thickness of about 12 cm (4-3/4 in.),

combustible materials will be ignited if maintained in long

continued contact with the chimney having flue gas temperatures of 400°C; while ignition of combustibles near

chimneys has been attributed to lack of tightness of the

chimney walls, it appears that ignition occurs because

of unsatisfactory insulation; if the expansion of a chimney is obstructed or restrained during a chimney fire,

cracks can be formed through the entire brickwork of the

chimney-thus , chimney brickwork should not support flooring

unless the chimney has an internal, independent flue, not

joined to the brickwork supporting the floor.
- 6 -

18. Residential Chimneys of Non-traditional Design,

Institute TNO voor Bouwmaterialen en Bouwconstructies

1961-1: Optimal chimney cross-section for furnace

output of 39*600 Btu/hr is round with diameter of

12 cm (4-3/4 in.); with this chimney in concrete of

6 cm. minimum thickness, the heat transmission

coefficient of the concrete in room-dry condition

not higher than 0.4 kcal/m.ho °C, and a constant

flue gas temperature of 600 degrees C above the

ambient, the temperature difference of the outer wall

surface with the ambient depends on the wall thickness,

and amounts to:

Wall thickness 6.0 6.5 7.0 7.5 8.0

Temp. Difference

on exterior 146 126 114 104 95

Advantages of concrete chimney with ceramic flue liner

over traditional brick chimney:

a. better draft and insulation

b. lower temperatures on outer covering

c. fewer cracks

d. no attack on mortar joints by flue gases or high

temperatures

.

Unlined concrete chimneys have lesser advantages over brick.

Disadvantages of concrete chimneys:

a. The resistance of concrete against attack by flue gas

is significantly lower than that of brick.

b. The heat resistance of concrete is less than that of

brick.

The report recommends:

a. Limiting cracks in an unlined chimney by use of

horizontal reinforcing.

b. Providing a ceramic pipe flue lining to limit effects

of gas attack and high temperatures, and to reduce

temperature- rise on the outer cover of the chimney.
- 7

-

c. Careful alignment of flue pipes, avoiding bulging

mortar joints.

d. A nonquartz-bearing porous aggretate, low watercement ratio in the concrete, density suitable for

vibrating.

19. Flow of Heat in a Room with Fire and Chimney, by

T. Ferguson, Engineering (London), Vol. 186, No. 4830,

Oct. 3? 1958, pp. 454-6: Heat loss from fireplaces

reduced by addition of an adjustable chimney throat

restrictor; data for airflow resistance of chimney

circuits

.

20. ACI Standard Specification for the Desigh and Construction of Reinforced Concrete Chimneys (ACI 505-54)

,

American Concrete Institute Journal 26 (1), 1954-55?

pp. 1-48: Formulas for determing temperature gradients

through concrete chimney shells.

21. Chimney Stacks Made of Precast Concrete Units, by

G. Heinicke, Betonsteinzeitung (Wiesbaden), Vol. 22, No. 12,

Dec. 1956, pp. 718-26: Describes requirements for chimney

construction of concrete block, and the technical and

economic advantages of the use of this material; Illustrates methods of framing roof members around chimney.

22. Observed Performance of Some Experimental Chimneys, by

R. S. Dill, P. R. Achenbach, J. T. Duck, Heating, Piping

and Air Conditioning, Vol. l4, April 1942, pp. 252-6:

Tests on two experimental, residential type chimneys

operating at various stack heights, gas flows and inlet

temperatures. Data for temperature gradients at different

levels in chimneys; also draft data; brick masonry

chimneys 38 ft high and 4 in. thick around a tile flue

liner (inside dimensions 7-1/4 by 7-1/4 and 6-1/2 by 11 in.)

Tests made at NBS.

23 . Fire Hazard Tests with Masonry Chimneys, by Nolan D.

Mitchell, NFPA Quarterly, Vol. 43, No. 2 Oct. 1949 (Reprint)

Tests of 21' different masonry chimneys (brick, tile, concrete block and chimney units), unlined and with ceramic

or vitreous enemeled steel liners; coal, wood, gas fuels;

tests indicate that unlined masonry chimneys present

greater fire hazards than do lined ones; liners should not

be rigidly fixed to chimney wall; round liners appear to

have some advantage over rectangular ones; concrete chimney
- 8 -

units having integrally cast liners developed cracks

through both the liner and masonry wall; the required

space between chimney wall and wood framing should

be left unfilled except that noncombustible fire

stopping may be used at the bottom (fills of mineral

wool between joists and chimney resulted in some" eases

of ignition of the wood) ; wood piaster grounds should

be removed; staying at floor or roof level should be

limited to contact with floor or sheathing up to 1-1/2 in.

from corners of chimney®

2b, Fire Hazard of Domestic Heating Installations , by

G. Q. Voigt, Bureau of Standards Research Paper RP 596,

Sept, 1933 : Tests with domestic stoves, furnaces and

their pipes; temperature rise on partitions, ceilings

and floors; effect of some protective materials; wood

ignition from short-time exposure at temperatures of

250 to 300°C; long-term exposure may cause ignition at

150°C; temperatures frequently exceeding 125°C (25?°F)

should be avoided, but temperatures of 150°C (302°F may

be occasionally tolerated; smoke pipes, uninsulated,

passing through combustible partitions require b-in.

vented airspace, or may be insulated with 2-in® mineral

wool; stoves having the fire box or ash pit directly on

the floor can transmit temperatures capable of igniting

wood through a b-in. thick brick base; if a 5-in, air

space is left between stove and floor, the floor should

be further protected with 1/b-in. asbestos or similar

material under sheet metal; the results indicate the

possibility of igniting wood forms left under brick or

concrete arches supporting fireplaces®

25- Residential Fireplace Design, Structural Clay Products

Institute, Technical Notes on Brick and Tile Construction,

Vol. 6, No. 10, Oct. 1955 : Description of parts;

National Building Codes recommendations; table of flue

sizes for different sizes and types (single face, two

face, etc.) of fireplaces.

26. Residential Chimney Design and Construction, Structural

Clay Products Institute, Technical Notes on Brick and

Tile Construction, Vol.® 3? No. 1, Jan 1952 1 Brick chimneys

b-in. thick with standard 8- x 8-in, flue liners; one

chimney, flue lining sections not cemented, space left

between lining and brick; another, flue linings bonded

and space between liner and brick filled solidly with

cement mortar; in tests, airspace had no effect on the

operation, and no appreciable insulating value; grouted

liner considered preferable on the grounds of greater
- 9

-

strength and ability to stay in place when cracked;

recommends standard construction and clearances from

combustibles (NBFU Standard Ordinance for Chimney

Construction)

.

27. Temperatures Developed in Chimneys for Low Cost Houses,

NBS Technical News Bulletin No. 328 , August 19^-, p. 62;

To establish performance requirements for tests of lightweight, prefabricated chimneys, tests were conducted

with lined and unlined brick chimneys having R-in. thick

clay-brick walls; floor joists framed 2 in. away from

chimney surface, but edges of floor boards and nailing

strips for base trim in contact; after approximately

13 hr for the lined chimneys and slightly less time for

the unlined, and with flue gas temperatures of 1100°F

and 900°F, respectively, hazardous temperature conditions

were created on surrounding wood.

28. The Heating of Panels by Flue Pipes, by D . I. Lawson,

L. L. Fox, C. T. Webster, DSIR, Fire Offices Committee,

Fire Research Special Report No. 1, London, HMSO, 1952 : Temperature rise of a vertical panel near a cylindrical

radiating surface may be computed; an asbestos shield

is effective in reducing the temperature of the panel;

advantageous to separate the shield and the panel, but

little additional temperature reduction in separations

greater than 1/2 in. ; metal shield probably even more

effective; theoretical and experimental derivation for

flue pipes not covered or enclosed; tests with solid

fuels

.

29. Clearances and Insulation of Heating Appliances, by

John A. Neele, Underwriters* Laboratories, Inc.,

Bulletin of Research No. 27, June 19*+5 : Heating of

adjacent woodwork by stoves and smokepipes; safe maximum

temperature for long-continued exposure of wood taken

as 90°F above room temperature ; thoroughly dried and

slightly scorched wood panels were found to develop

higher temperatures on the surface than they did when first

used; in order not to exceed the maximum 90°F rise, a clearance of 7 in. would have to be provided between a wood panel and a smokepipe at 450°F.
- 10

30. Performance of Type B Gas Vents for Gas-Fired Appliances,

by L. M. Kline and H. Witte, Underwriters' Laboratories,

Inc. Bulletin of Research No. 51, May 195^9 • Tests to

determine the temperatures of flue gas through different

vent systems; heat sources were a central furnace, a floor furnace, water heater, unit heater and room heater;

four styles of vent pipes (double-wall with 1/2- and

lAf—in. airspace, single-wall and asbestos-cejnent )

,

mostly 3-and 5-in. diameter; temperature rises of flue

gases at inlet of draft hoods and of vents, of vent

pipe walls, and on walls of vent pipe enclosures; least

heat transmission with double-wall metal pipe with

1/2-in. airspace; also included in the report was a survey of the ignition of wood exposed at high temperatures

for long periods of time, from which it was concluded that

such exposure should be limited to 90°F above room temperature.

Underwriters' Laboratories, Inc. Standards for Safety,

Gas Vents UL 44l, Factory-Built Fireplaces UL 127 and Chimneys,

Factory Built UL 103 have requirements for maximum temperatures

on enclosures for the parts, or on the vents, fireplaces or

chimneys at points of zero clearance from combustible members of

a structure that generally reflect a 90°F rise limitation.

Under certain circumstances of abnormal conditions of firing

or operation wherein excessive temperatures, usually of short

duration, may arise in a flue or fireplace, a greater temperature rise on surrounding structures is permitted. In no

case, however, is the specified limiting rise greater than

175°F.

A study of NBS informal reports to several Government

agencies, and the considerable body of correspondence on

fireplaces and chimneys reveals some information, although

in at least a few instances, it appears to be based on the

results of other works, including those reviewed herein.

In tests of prefabricated enameled metal chimneys for

solid or liquid fuel furnaces in war emergency housing, a limiting rise of 3 75 degrees F on the outer surface of the

chimney covering was established for a flue gas temperature

of 1000°F. This condition was considered to offer protection

to the combustible framing and woodwork spaced a minimum of

2 in. from the chimney. It was concluded that satisfactory

insulation could be achieved with asbestos paper plies totalling about I-3A in. in thickness and having a low combustible

content, 5 pen cent or preferably less. Some asbestos-cement

pipe coverings were also found to be capable of reducing

heat transmission to the required extent.
- 11 -

The following points are made in letter correspondence

of the Bureau:

In venting an oil burning floor furnace below combustible floor construction, the possible existence of

a flue gas temperature of 1000°F must be considered.

If this temperature prevails on the outer surface of

the flue, unprotected combustible floors must be

spaced 12 in. from the chimney, and columns or walls

9 in. away. Spacings can be reduced by one half if

protection such as 1/8-in. asbestos millboard is placed

in the air space between the flue and the wood.

Bonnet temperature above a coal-fired forced warm air

furnace was 48l°F when the flue temperature was 1360°F.

At a point in a branch duct 4-1/2 ft from the top of

the combustion chamber, the temperature was 400°F.

Solid foundations were not recommended for use under

domestic heating plants where the foundation is in

contact with combustibles; preferably there should be an

open air space between combustion chamber and cement

floor. States that a solid foundation has transmitted

enough heat from the firebox to ignite combustible

material beneath it.

Cement-asbestos flue pipe suitable for gas-fired stoves

only.

No record of fires traceable to heat conduction through

a properly built brick chimney.

Blanket-type Insulation of mineral wool bound to flue

with asbestos paper and woven wire fabric was satisfactory, but not premolded insulations of mineral wool or

fiber glass (combustible binder).
12

3 • Recent Works Not Included in Review

31. Chimney Fires, Fire, 1958, 51 (639) 197, 200.

32. Chimneys and Fire Protection (Swed.), A. H. Bergquist,

Byggmastaren 1958, 134, 77-80.

33* Modern Flue and Chimney Construction, Bldg. Mat. 1958,

18(2), 69-70.

3k. Structural Fire Protection, Fortschritte u. Forschungen

im Bauwesen, Reihe D, Heft 27, Franckh'sche

Verlagshandlung , Stuttgart 1957 (Fire resistance of flues

of standard masonry and of lightweight concrete castings)

.

35. Experimental Observations Concerning Cracks in Flues,

Claudon and Tirel, Ann. Inst. B&tim. 1958, 11(121), bCr-^2,

36. Thermal Stresses in Flues, J. Tirel, Ann. Inst. Batim.

1958, 11 (121), 28 - 39 .

37. Domestic Flues, P. Becher, Industries Thermiques, 1957,

( 11 ), 655- 65 .

38 . Theory of the Construction of Chimney Flues, R. Cadiergues,

Industries Thermiques, 1957, (11), 689-701.

39. Gas Flues, Archit. (Build.) J. 1958, 127 (3295), 624-34.

40. The Cracking of Flues, CSTB (France), Cahier 238, 1957.

41. Materials for Flues, A. Claudon, Industries Thermiques,

1957, (ID, 666-88.

42. The Design of Domestic Open Fires, D. K. Darby, Plumber,

1958, 80 (1949) 45-50; (950) 43-4.

43 . Space Heating and Associated Fire Hazards, Booklet No. 33,

Fire Protection Assn. , London, 1957.

44. Lighweight Concrete Shaped Blocks of up to 700 cm Section,

Standard DIN 18150, Deutscher Normenausschuss , Berlin, 1956.

45. Oil Fired Domestic Boilers and Air Heaters for Hot Water

Supply* and Space Heating: Safety Recommendations^ Bookrle!

No. 31, Fire Protection Association, London, 1957.
- 13 -

46. Fire Hazards of Chimneys and Flues, Technical Information

Sheet 1001, Fire Protection Association, London.

47. Maximum Temperatures Attained in Chimney Flues, A-. Claucton,

Industries Thermiques, 1957, 3 (1), 21-40.

48. Fire Tests on Domestic Chimneys, by H. Seekamp and K. Mohler,

Verl. von Wilm. Ernst u, Sohn, Berlin, 1956.

49. Aluminium-Sheet Chimneys, Light Metals Bui., 1956, 18 (8),

316.

50. Flue Pipes and Combustible Materials, Fire Prot. Assn.

Journal, 1956 ( 33)9 207.

51. Flue Piping Causes Fire, Fire Protection (Rev.), 1956, 19

(185), 178.

52. Temperatures on a Wood Ceiling about a Furnace Plenum,

R. Ditsworth, Heat. Air Condit. Contract. , 1955, 27 (2)

( Issue 715) , 31-7.

53* Chimney Fires, Prot. Civile (France), 1956, ( 23 ), 46-7.

54. The Fireproof Chimney, Bayerischen Versicherungskammer

,

1959.

55* The Protection of Floors under Fireplaces, F. Mayer,

Osterr. Feuerwehr, 1955? 9 (1), 8 - 9 .

56. Tentative Code of Minimum Obligatory Conditions for the

Fixing of Fire-Grates and Associated Conduits, Ann. Inst.

Bsitiment, 1955? 8 (94), Supp.

57* Design of Heating and Ventilating Systems, F. W. Hutchinson,

N. Y., The Industrial Press, 19554

58. A Guide to Current Practice, Inst, of Heat. Vent. Engrs,

London 1955*

59* Asbestos-Cement Flue Pipes and Fittings, Light Quality,

BS 567: 1954, British Standards Institution, London.

60. Domestic Fireplaces and Chimneys, Commonwealth Experimental

Bldg. Sta. Dept, of Works and Housing, Australia, Notes on

the Science of Building, No. SB3 I? Chatswood, N.S.W.,

Sept. 1954.
61

62,

63.

64.

65 *

66 .

67.

68 .

69.

70,

71.

7 2.

73.

74 .

14

Prefabrication in Traditional House Building I, N, .3 , Pippard and W. G. Buckle, Prefabrication, 1954, 1 (7),

15-8 (Brit, prefab, brick chimney stack).

Fire Incidents with Fireplaces, Flue Pipes and

Chimneys, R. Quester, Osterr, Feuerwehr, 1953 ^ 7 (3)

47-7, 49.

The Hazard of Domestic Fire, J. F. Fry, J. Roy. Inst,

Brit. Archito, 1953? 61 (1), 18-20

Fire Tests on Chimneys, S. Ausobsky, Osterr. Feuerwehr,

1952, 6 (12), 234-6.

Structural Timber under the Hearth, Fire Prot. Assn. J.,

1952 (19), 307-8.

Flue Pipes and Hearths, Norsk Brannvern Forening, Oslo,

Sept. 1952.

New Documents on Flue Construction, Ribaud, Puteaux,

Fournol and Gouffe, CSTB (France), Cahier 111, 1951-

Regulations and Instructions on the Venting of Domestic

Gas Heating Appliances, 0. Rosier, Gas, Wasser, Warme,

1951, 7 (1), 6-16.

Domestic Chimneys, P. Becher, Statens Byggef orskningslns ti tut

,

Studie No. 6, Copenhagen, 1951.

Fire Resistance Tests on Chimney Blocks and Glass Panels,

K. Walz and J. Strey, T.I.Z., 1951? 75 (13/14), 203-8.

Flues for Domestic Appliances Burning Solid Fuel, Brit.

Stds. Instn .

, Council of Codes of Practice for Bldgs.,

CP 131.101 (1951), London.

Domestic Hearths. Fires Due to Defects, Fire Prot. Assn.

J. , 1951 (12) , Jan. 9-11.

Three Hazards that Need Watching, Doors, Flues, Water

Heaters, Fire Protection, 1951? l4- (130), 317-8.

Smoky Chimneys, Bldg. Research Sta., B.R.S. Digest No. 18,

May 1950. (Principles of correct design of fireplaces and

flues). ••
- 15 -

75* Chimney Constructions and Dimensions of Bricks, Virtala

and Koskela, Valton Teknillinen Tutkimuslaitos , Tiedoitus

40 and 43, Helsinki, 1947.

76. Drawings of the Principles of Construction of the Swedish

Fire Prevention Assn. , Svenska Brandskyddsf oreningen.

Stockholm 1946 (construction of fireplaces and flues).

77* Precast Concrete Flues, Concrete Building, 1946, 21 (8),

103-7.

4. Available Information for FHA Proposal 1.26

It appears that some of the material covered in the

Bibliography of Papers Available for Review at NBS (Section 2)

gives, or, at least, suggests answers to some of the questions

in Proposal 1.26 (see Appendix A). Each of the 18 questions

will be considered briefly, and where possible, reference will

be made, by number, to the papers reviewed in the bibliography.

1. Reference 7 recommends an effective flue area 1/12 area

of fireplace opening. References 8, 10, 19 stress importance of restricting chimney air flow to increase efficiency

of open fire. Reference 25 has a table of flue sizes for

different sizes and types of fireplaces (no indication of

source data )

.

2. No precise data seems available. Reports stress importance

of preventing downdrafts and other erratic behavior caused

by wind. Minimum would require consideration of many

atmospheric conditions. Reference 7 states 30 to 35 ft

minimum chimney height required to secure good draft and

avoid misfunction.

3- References 4 and 6 describe tests of chimneys with brick

liners (separated from outer brickwork by mineral wool

layer) . Lightweight concrete block chimney units are

described in 13-16, 21. The advantage of concrete chimneys,

especially with ceramic liners is shown in reference 18 , which also gives a table of temperature differences from

the ambient as a function of wall thickness of concrete

chimneys (fixed flue gas temperature and concrete heat

transmission coefficient). In reference 23 it states

that; unlined masonry chimneys present greater fire hazard;

concrete chimney units with integrally cast liners developed

cracks* through both liner- ahd- rnsonry wall.
16 -

4. Air space or soft mortar fill required to allow movement

of inner liner and minimize cracking (references 4, J. 7', 23 ) . However, reference 26 states that grouted liner is preferable in that it has greater strength and ability to stay

in place when cracked.

5. References 9, 17, 2 7 describe the development of hazardous

conditions on the surface of masonry chimneys. Filling

the 2 -in. space between joist and chimney resulted in

some cases of ignition of the wood (reference 23 ) . Tests

show that ignition temperatures of wood are significantly

lower after long continued or even intermittent exposure

at elevated temperatures (references 24, 29 )°

6 . No precise data, but reference 23 indicates that flooring

or roof sheathing may be in contact with a masonry

chimney up to 1-1/2 in. in from corners of chimney. In

tests described in reference 27 , in which edges of floor

boards and nailing strips for base trim were in contact

with brick chimneys, hazardous temperature conditions were

developed on the wood.

7. Reference 23 states that this practice Is satisfactory on

masonry chimneys.

8 . There do not appear to be any data. Regulations stating

that there must be a 2 -in clearance of combustibles, or

combustibles may be 6 in. from flue liner seem to equate

2 in. of masonry with a 2 -in. airspace. (see reference 23

for effect of mineral wool between chimney and joist).

9. No references on chimney caps. It would appear that this

part, which is subjected to severe conditions (thermal

stress, attack by flue gas, effect of freezing and thawing,

action of movement of chimney liner), should not be changed

if the MPS design has proved satisfactory.

10.

Reference 24 states that temperatures capable of Igniting

wood occurred through a 4-in. thick brick base from a stove having its fire box directly on the floor. For such

stoves (and by analogy, fireplaces ) recommends a ^~±n<, airspace between stove and floor and further protection of

floor with I/4-in. asbestos under sheet metal.
- 17 -

11. No data found. A little information available on brick

fireplaces, but not on concrete masonry. Comparison of

concrete masonry fireplace construction with concrete

chimneys does not appear valid, as the chimney, except

at the rare and relatively brief occurrence of a soot

burnout, is not subjected to flame as is the fireplace

structure

.

12. Reference 9 gives temperatures on outer surface. of a 9-in.

brick wall (265°F under a 1-in. board after 12 hr maximum

-firing).. It would appear that the provisions of Underwriters' Laboratories, Inc. Standard for Factory-Built

Fireplaces, UL 127, would apply to steel fireplace liners.

13 . Do not appear to be actual test data, but data from other

tests indicating the temperature rise to be expected on

combustibles at a distance from a heated surface may be

applicable if temperatures on fireplace walls are obtainable (references 28,29).

14. Reference 9 states that the 4-in. wall behind a fireplace

is allowed as an external wall only, in Britain. . Figures

in this reference indicate that a 9-in. brick wall would

not limit the temperature rise on combustibles in contact

as required by UL Standards (References 29, 3D).

*15* No information on material of hearth.

16. No actual data on hearth extension. UL quotes National

Code for outer hearth dimensions in UL 127, Factory-Built

Fireplaces

.

17- No references except UL 127 on placing combustible material

near edges of fireplace opening. It would appear that

effectiveness of fire screen may be a factor. Also, too

close positioning of combustibles on face of fireplace to

opening could possibly negate the intent of requirements

specifying a minimum thickness of masonry.

18. It appears that this is covered by UL 127 on FactoryBuilt Fireplaces which states (para. 42) that insulating

materials required to protect combustible parts of the

building shall be supplied as an integral part of the

fireplace assembly.
18

5. Conclusions

A study of the available material on chimneys and fireplaces has indicated answers to some of the questions proposed

by FHA. Information pertinent to the specific points of

inquiry have been presented herein, together with collateral

material that may also have a bearing on the requirements of

the Minimum Property Standards.

The amount of research being conducted at present on the

fire hazards of chimneys and fireplaces is apparently very small.

An examination of the Directory of Fire Research in the U. S.

(Publication 904, NAS-NRC, 1961) Indicates that no effort

whatever is being expended in this direction. European work

also Is, at best, extremely limited. The results, too, are

often not fully applicable to conditions here, as considerable

differences may exist in materials, fuels and thermal output

of heating units. For this reason, and also because it appears

many workers are mining the same field, it is considered that

a review of the papers in Section 3 would not yield data of

any great significance, and quite possibly not compensatory of

the effort required to secure them.

It would seem that the material presented here already

answers some of the more important questions raised in Proposal

1.26. Where specific information is lacking, standards for fire

safety, which must cover not only ordinary but the worst possible

conditions, should err on the side of overprotection.

Further information is, of course, obtainable through

research in any areas of interest the Federal Housing Administration may have. Specific recommendations cannot be made,

however, without an indication of these particular interests.

Such tests would be extensive and costly as the factors involved

in any study would be numerous and complex. In lieu of this,

it is suggested that use be made of all available data, supplemented where needed by the store of knowledge of good construction gained through practical experience. That reliance on

the data and experience is a suitable course is evidenced by

the fact that observation, as well as the meager available

statistics on the causes of fire has indicated that fireplaces

and chimneys are only a minor factor in fires occurring in

residential properties.
-19 - APPENDIX "A”

PROPOSAL FOR STUDY OF

CONSTRUCTION AND DESIGN OF CHIMNEYS AND FIREPLACES

1.0 STATEMENT OF THE PROBLEM

A. Minimum fire protection construction and clearances between

chimneys and fireplaces and adjoining combustible materials

need to be determined.

B. Fundamental dimensions and design arrangements required to assure satisfactory performance of fireplaces and chimneys

are needed for the Minimum Property Standards.

2.0 BACKGROUND

The Minimum Property Standards spell out minimum clearances for

fire protection of combustible materials. They also provide

dimensional limits for the design and arrangement of chimneys

and fireplaces.

Tests have been conducted by Underwriters' Laboratories, the

National Bureau of Standards, and private schools and laboratories to establish safe relationships between potentially hot

surfaces and adjoining combustible materials. In addition, the

National Fire Prevention Association and the National Board of

Fire Underwriters have developed codes which specify many of

the nominal clearances that must be maintained in building

construction.

Despite the extensive research that has gone on, there are still

many fire clearances in modern building structures that have not

been definitely determined by actual experimentation or tests.

Moreover, there are inconsistencies in design and arrangement of

present day fireplaces and chimneys that have never been resolved

At the present time, the MP3 ' s are based on information obtained

primarily from building codes or from judgments of the FHA staff.

Although codes are a satisfactory source of such information to

FHA, requirements contained in the various codes differ widely

when compared one with another. Moreover, it appears that some of these requirements are based on compromise opinions rather

than tested facts. FHA believes these differences and opinions

need now to be resolved by actual tests.

This proposal outlines the major areas in which MPS requirements

for fire protection of combustible materials and for design and

arrangement of chimneys and fireplaces are believed to be inadequate. It is suggested that a program of tests be inaugurated

to provide factual answers.
OJ

20

.0 QUESTIONS

Answers are needed to unresolved questions arising from the MPS

such as the following. Others should be added as the study progresses and their needs are recognized.

Chimneys

1) What should be the relationship between chimney flue area

and fireplace opening area for various chimney heights and

fireplace arrangements?

2) What should be the minimum height of chimney extension beyond the highest point of the adjoining roof?

,

3) If fire clay liners are omitted from masonry chimneys, what

kind of brick or block at what minimum thickness should be

allowed?

k) Most codes require l/2" air space between the flue liner and

the surrounding masonry of chimneys, yet the West Coast allows

this space to be filled with mortar. Is this air space really

necessary?

5) Most codes agree that a 2" air space should be required between wood framing members and the masonry chimney wall . Is

this realistic in light of actual experiences and tests?

6) What air space should be required, based on actual tests,

between masonry chimney walls and subflooring, flooring and

roof sheathing, respectively?

7) According to most codes, furring strips not wider than lV

may be installed with zero clearances at corners of chimneys.

Is this realistic in light of actual tests?

8) The MPS states that piers built integrally with the chimney

for support of wood beams or girders may be used provided

the wood is separated from chimney masonry with at least 2"

air space. If more masonry is used, by how much may this

2" space be reduced?

9) The MPS requires a chimney cap of concrete. or other waterproof noncombustible material with a minimum thickness of

2" at the outside edge. What limitations on design, materials, dimensions and reinforcement should be imposed on this chimney cap?
21

Fireplaces

10) The MP3 requires that fireplaces be supported on concrete or masonry, yet San Francisco permits fireplaces to be supported

on frame structures provided certain fire-preventing measures

are met. What limitations should the MP3 impose on fireplaces supported by frame structures?

11) The MPS requires that concrete masonry fireplaces shall be

made of solid units, yet chimney liners may be constructed

with air spaces. What kind of construction should be required

for concrete masonry fireplaces both with and without fire

brick liners?

12) Where a fire brick liner is not provided for a fireplace

firebox wall, the MPS requires a masonry wall thickness not

less than 12", but does not state the type of masonry to be

used. What kind of brick or block of what total thickness

may be substituted for the lining? If a steel fireplace liner

is used, what wall thickness and air space should be required?

13) The MPS requires certain minimum air space separations between

various combustion materials and the fireplace walls. According to actual tests how much should these air spaces be?

lh) The MPS and most codes state that fire clay purging may be

omitted if the fireplace wall thickness is at least 8", yet

the same codes require as little as a b" vra.ll thickness behind the smoke chamber. What minimum thickness of masonry

should be used according to tests as a substitute for re- fractory linings in the principal high temperature zones?

15) Codes permit hearths to be constructed of brick, concrete,

stone, and tile, yet these materials spall when heated ex- cessively. Of what materials according to tests should the

hearths be constructed?

16) The MPS gives hearth dimensions in relation to fireplace

openings. According to actual tests, how far should the

outer hearth extend? May it be omitted completely? What

limitations should be placed upon a raised hearth?

IT) Codes require that combustible materials should not be placed

within 6" of the edges of a fireplace opening. The MPS re- stricts this to 3y" • What dimensional restriction should be

placed upon location of combustible materials near fireplace

openings?

l8) The MPS requires the outer hearth for factory-built fireplaces to be made of noncornbustible materials not less than
- 22

3/8" thick which may be placed upon subfloor or finish floor.

What restrictions should be made in adapting factory-built

fireplaces to combustible materials in the structure?

k.o priority

Although the MPS is being completed now for publication, the

information is still needed to answer questions from FHA field

offices and to prepare technical bulletins for distribution in

conjunction with the MPS. The information obtained will be useful not only to FHA but to code-writing organizations, insurance

companies and the building industry as a whole.

5.0 REC OMMENDATIQMS

None

.

USCOMM-NBS-DC
U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

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In general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover. WASHINGTON, 0. C.

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Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standard Refer- ence Materials. Applied Analytical Research. Crystal Chemistry.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls. Polymers. Macromolecules: Synthesis and Structure. Polymer Chemistry. Polymer Physics. Polymer Characterization. Polymer Evaluation and Testing. Applied Polymer Standards and Research- Dental Research.

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and Metal Deposition.

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