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Chimney Fundamentals And Operation

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1 Chimney Fundamentals And Operation
The Art of Venting Flue Gases Or How Not To Kill Your Client Presenter: Earl Hicks

2 Objectives Review New York WAP policy regarding venting systems
BPI Standards Review combustion process Define & understand combustion air How does a vent system work Identify venting categories and materials Using venting rules-of-thumb Inspection of existing flues Alternative venting methods Before beginning, select 2 volunteers to do the glass and straw experiment. Mark a 1” scale approximately 1” from the bottom of a straw. Create 10 segments, tenths. Pour water in a glass to the lowest mark on the straw One volunteer sucks water to the first tenth mark indicating .1”WC draft, 5 to 10 times normal draft. Discuss the draft pressure

3 NYS WAP Policy Ensure safe elimination of flue gases from the building

4 BPI Standards Building Performance Institute
Any combustion appliance chimney/vent system that is in use must be visually evaluated for defects A deteriorated chimney should be repaired or relined and causes corrected before reusing.

5 Principles Of Combustion
Three essential components for combustion Fuel Oxygen Heat Fuel – Fossil fuels Oxygen – Air is 20.9% O2 Heat – Pilot, spark, or igniter The objective of the next series of slides is to impress upon the techs the volume of gasses that must be vented, what they are and how they are produced. This will lead into the differences of volume of gasses, draft hood vs. induced draft appliances.

6 Combustion Principles

7 The Chemical Reaction CH4 + 4O2 + heat = CO2 + 2H2O + heat
Complete combustion Natural gas 1 Cu Ft of CH Cu Ft of air for complete combustion 11 Cu Ft of flue gases

8 Combustion Air Must supply sufficient air for complete combustion when all appliances are in operation simultaneously. Must determine whether CAZ is a confined or unconfined space per NFPA. Tightening a dwelling too much may result in the need to bring in outside air for combustion regardless of NFPA classification. Must follow established standards for bringing in combustion air. Sufficient Combustion air is important to the equation. Explain that this is why when we complete evelope/shell measures such as intentional air sealing, or unintentional airsealing via densepac insulation that we must conduct a CAZ and blower door test at the end of the day.


10 Confined / Unconfined Confined Space Unconfined Space
Not enough air in the combustion appliance zone to provide for complete combustion when all appliances are operating and the building is set in worst case criteria. Unconfined Space Enough air is present to provide for complete combustion when all combustion appliances are operating and the house is set for worst case criteria.

11 Standard 1/20 Rule Measure the volume of the CAZ.
Add all input Btu ratings of appliance in the CAZ. If dryer is in CAZ Electric – consider input rate of 100,000 Gas – consider input rate of 125,000 Divide this total Btu by 20. The resulting number is the Cu. Ft. separating confined from unconfined space. Volume of CAZ below result = confined space Volume of CAZ above result = unconfined space

12 Example CAZ = 10’L X 14’W X 8’H Appliances
Gas furnace – 75,000 Btu input Hot water heater – 40,000 Btu input Gas dryer - 125,000 Btu input

13 Solution CAZ = 10’L X 14’W X 8’H Total appliance input Btu 1/20
Volume = 1120 Cu’ Total appliance input Btu 240,000 Btu 1/20 240,000 ÷ 20 = 12,000 cu ft. Actual volume is below 12,000 cu ft CAZ is a confined space Results: Additional combustion air must be brought into the CAZ

14 Other Than Standard: IMPORTANT! The above standard is based on a known infiltration rate of less than .4 air changes per hour When the ACH is known For appliances other than fan-assisted, consult NFPA (1) For fan-assisted appliances, consult NFPA (2)

15 Table Natural Draft Appliances
Using a blower door, ACH can be measured and a more accurate picture of the amount of combustion air that is available is obtained.

16 Table Fan Assisted Appliances

17 Methods of Bringing In Combustion Air
Within the dwelling, from other zones Ducted in horizontally from OD Directly from OD above and or below

18 What is Draft Negative pressure within a flue that pulls products of combustion out from the dwelling.

19 Factors That Affect Draft Pressure
Delta T, Indoors to Outdoors Height of Vent Interior Volume Restrictions Atmospheric Conditions Pressure Imbalances in the CAZ

20 How Does A Venting System Work?
Air Flow “Natural” draft is actually thermal draft and occurs when gases that are heated expand so that a given volume of hot gas will weigh less than an equal volume of the same gas at a cool temperature. Since hot combustion gases weigh less per volume than room air or outdoor air, they tend to rise. The rising of these gases is contained and increased by enclosing the gases in a tall chimney. The vacuum or suction that you call “draft” is then created throughout this column of hot gases. “Currential” draft occurs when high winds or air currents across the top of a chimney create a suction in the stack and draw gasses up. “Induced draft” blowers can be used in the stack to supplement natural draft where necessary. There are three factors which control how much draft a chimney can make: The height of the chimney – the higher the chimney, the greater the draft The weight per unit volume of the hot combustion products – the hotter the gases, the greater the draft. The weight per unit volume of the air outside the home – the colder the outside air, the greater the draft. Since the outside temperature and flue gas temperature can change, the draft will not be constant. When the heating unit starts up, the chimney will be filled with cool gases. After the heating unit has operated for a while, the gases and the chimney surface will be warmer, and the draft will increase. Also, when the outside air temperature drops, the draft will increase. The best way to be sure the burner does not depend on this air is to set the burner for smoke-free combustion with a low over-fire draft (.01 to .02 inches of water). If a burner cannot produce good smoke-free combustion under low draft condition, there is something wrong with the burner or combustion chamber, and it should be corrected. Combustion Gases

21 What is Considered Adequate Draft?
OD temp >800F, >-1 Pa or ”WC OD temp 300 – 800F, >-2.5 Pa or -.01”WC OD temp below 300F, >-5 Pa or -.02”WC (250 pascal = 1”W.C.)

22 Most Common Poor Draft Factors Found in the Field
Return air leaks in the basement Long horizontal vent connectors Blocked vents Deteriorated flue Bird nests Outside masonry flues with fan assisted heating appliances Fireplaces with no outside combustion air and without front enclosures. Overly tight houses


24 Venting Categories

25 Venting Categories NFPA 54 and 58 criteria Standardized Category I
Negative pressure, non-condensing Category II Negative Pressure, condensing No longer produced Category III Positive pressure, non-condensing Category IV Positive pressure, condensing I attempt to use this information to illustrate differences, concentrating on categories I and IV.

26 Non-Condensing Condensing
Appliances that are categorized for the purpose of vent selection are classified into the following four categories:

27 Category I What we normally think of when we think chimney
Negative pressure sucks products of combustion from the appliance breech and deposits them outdoors Category I Appliance: Operates with neutral/negative vent static pressure, flue gas temperature does not exceed 550 degrees, and conforms to NFPA 54 & UL 441 (B Vent). This appliance takes combustion air and chimney draft dilution air from within a building, is installed with a draft hood, draft regulator, or other means of allowing for regulation of dilution air, and depends upon natural draft to vent products of combustion to the outdoors. For example, such an appliance includes a fireplace, wood stove, natural draft furnace, boiler, water heater, or gas range. This type of combustion appliance is the most sensitive to backdrafting.

28 Category II No longer manufactured
Negative pressure vent with combustion gases at or below the dew point Heavy gases at the dew point are not buoyant enough to vent with a negative pressure flue Category II Appliance: Operates with neutral/negative vent static pressure, flue gas temperature is less than 140 degrees (F) above dew point temperature. May cause excessive condensation and conforms to NFPA 211 and UL 1738 (Corr/Guard). Condensed water resulting from the removal of latent heat from steam. In the case of a high efficiency category II or IV boiler, the condensate is corrosive to 304/316 stainless steel. UL 1738 (Corr/Guard).

29 Category III Direct sidewall vented without additional apparatus.
Positive pressure requires joints in flue material to be sealed Because these 80% appliance flue gases are close to the dew point, and the vent material is single wall, corrosion resistant materials must be used Drains are typically incorporated to remove flue condensation before it enters the heat exchanger Category III Appliance: Operates at a positive static vent pressure (at the appliance) at a temperature that does not permit condensation. Conforms to NFPA 211 and UL 103 (PIC, IPIC, PSW).

30 Category III Has been used to solve installation problems where no appropriate flue is available Positive pressure requires joints in flue material to be sealed

31 “Z” vent being the most common material used today for category III.

32 Category IV Positive pressure condensing appliances, joints must be sealed 90%+ AFUE Appliances are designed to dispose of flue condensate as well as condensate formed within the secondary heat exchanger May be able to sidewall vent at reduced distances to openings in the building than NFPA suggests Sealed combustion Combustion air intake in same pressure plane Category IV Appliance: Operates at a positive vent static pressure, flue gas temperature is less than 140 degrees (F) above dew point temperature. May cause excessive condensation and conforms to NFPA 211 and UL 1738 (Corr/Guard). Condensed water resulting from the removal of latent heat from steam. In the case of a high efficiency category II or IV boiler, the condensate is corrosive to 304/316 stainless steel. PVC used because the vent temperatures are under 180 degrees. The advantage of high-efficiency appliances is that they significantly reduce the amount of gas consumed with no loss in output. A mid-efficiency appliance uses one-third less gas than a conventional appliance, and a condensing appliance uses only one-half of the gas of a conventional appliance. The savings in fuel are offset by higher first cost and the higher maintenance requirements of high-efficiency appliances, as well as the added cost of the electricity to operate the fan. 

33 Category I Vent Materials Found With Older Heating Appliances
Single wall galvanized pipe, 26 gauge Only as a connector on 70% AFUE and lower gas appliances and all oil appliances Connector for oil appliances Masonry Vitreous clay liner Oil appliances Transite Rated as single wall Asbestos Does not meet any venting requirements

34 Category I Vent Materials cont.
“B” Vent – double wall Galvanized steel outside, aluminum inner pipe Rated only for gas appliances Used as a vent connector for all 78% and 80% AFUE appliances May not be run outside of the building Used as a liner in an existing flue chase

35 Category I Vent Materials cont.
Flexible liner Aluminum – gas appliances Stainless Steel – gas and oil appliances Used to retrofit existing flue passages to meet code or a specific application “L” Vent – double wall Inner and outer pipes are stainless steel Oil appliances All Fuel, double wall insulated Oil Solid Fuels

36 Category III Flue Materials
Aluminum No longer recommended because of corrosion problems Stainless Steel Use type specified by manufacturers to reduce corrosion issues High temperature plastic Was the most common material specified by manufacturers Have been involved in recall Manufacturer specific installation protocol Sealed joints, High temperature sealant Hanger spacing Pitch back to appliance ¼” per Ft.

37 Category IV Flue Materials
PVC Low cost Sealed joints Must be provided with adequate hanging support Pitch – back to appliance ¼” per Ft. CPVC Higher operating temperatures than PVC Follow manufacturer instructions Manufacturer specific Sealed Joints FasNSeal® Special Gas Vent System for Category II, III & IV Heating Appliances. FasNSeal® is manufactured from AL29-4C®, a superferritic stainless steel.

38 Water In The Flue Water is a byproduct of combustion
Key for category I appliances is to maintain water in a gaseous state within the flue so that it exits to the outdoors. Category IV appliances are engineered to remove liquid water from within the secondary heat exchanger and flue.

39 Impress that water must be kept in a gaseous state for category I appliances.

40 93#(lbs) ~ 10 gallons Million Btu = 100, Hrs run time 10 Hr run time for natural gas = 10 gallons of water that must be removed from the flue.

41 70% AFUE Gas Furnace Overview
21 Cu Ft flue gases for every 1 Cu Ft of natural gas burned Draft diverter mixes the extra ~10 Cu Ft of air with the flue gases before entering the flue Reduced efficiency means more heat going up the chimney, hot flue gases (4500 – 6000F) Dilution gases reduce the relative humidity and increases the dew point

42 Draft Hood Appliances 1 Cu Ft CH Cu Ft air + 10 Cu Ft of dilution air mixed at draft hood 21 Cu Ft of flue gases up chimney under maximized conditions Draft hood aids in minimizing fluctuation of draft Prevents backdraft from affecting burner Spill Switch

43 78% & 80% AFUE Furnace Venting Overview
Draft induced fan does not force flue gasses into the vent. A category I flue of adequate design must be used More heat in the building and less up the chimney yields a colder chimney Cycle time is longer than older furnaces to adequately warm the flue and keep moisture in a gaseous state.

44 TO WARM UP A CHIMNEY If firing rate = 100,000 Btu/hr and SSE = 75%, then 75,000 Btu/hr go to the distribution system and 25,000 Btu/hr go through the vent If the burner on-cycle is 12 minutes (.2 hrs), then during one cycle the vent receives: hr x 25,000 Btu/hr = 5,000 Btu/cycle MASONRY CHIMNEY: A masonry chimney (block or brick + tile liner) requires about Btu/.ft. to go from 0o to 120o. So, on a very cold day, about one foot of chimney will be warmed in one burner cycle: 5,000 = 1 ft/cycle TYPE B-VENT CHIMNEY: A 6" B-vent chimney requires about 90 Btu/.ft. to go from 0o to 120o. So, 5,000 90Btu/ft = 55 ft/cycle

45 After Weatherization with a New Furnace:
If firing rate = 75,000 Btu/hr and SSE =82%, then 61,500 Btu/hr go to the distribution system and 13,500 Btu/hr go through the vent. If the burner on-cycle is 6 minutes (.1hrs), then during one cycle the vent receives: .1hr x 13,500 Btu/hr =1,350 Btu/cycle EXISTING MASONRY CHIMNEY: About four inches of the existing masonry chimney will be warmed during one burner cycle: 1,350 4,570Btu/ft = .3 ft/cycle TYPE B-VENT CHIMNEY: During each burner on cycle, enough heat to warm 15feet of B vent goes into the chimney: 1,350 90Btu/ft = 15 ft/cycle


47 Draft Induced Category I Venting Guidelines
No exterior masonry chimneys without a properly sized metal liner. Flex or “B” No interior masonry chimneys over 2 stories No transite chimneys No unlined masonry chimneys No masonry chimneys unless common vented with a draft hood type appliance without a vent damper These guidelines came from Carrier Corp literature in the mid 1980’s. Pretty much common installation guidelines today.

48 Draft Induced Category I Venting Guidelines (cont.)
Must have double wall “B” vent connector Furnace must be properly sized Furnace must be set up correctly Temperature rise Gas input Heat anticipator or cycle rate 3 cycles per hour Vent sizing should be in accordance with tables supplied with the furnace or NFPA When sidewall venting a power vent kit must be used unless the manufacturer specifies otherwise. Some utilities require “B” vent connectors on new installations before gas is turned on. Check your area.

49 New Category I Venting Rules-Of-Thumb
Use “B” vent as connector from the appliance to the flue Reduce heat loss in the connector Pitch connector down toward appliance ¼” per Ft. Warm air rises Maximum horizontal distance (Table ) 1 ½ times the diameter of the connector in feet 4” connector = 6’ maximum horizontal distance

50 Rule-Of-Thumb Continued
Follow NFPA 54 sizing charts Never used unlined masonry flue Don’t use outside masonry flue Never use Transite If you take the heating appliance out of the flue and leave the water heater in, you are responsible to ensure the water heater will vent properly Line the flue

51 Oil Appliance Venting NFPA 31 sizing guidelines Masonry Type “L”
stainless steel All fuel Oil sizing tables are less extensive. Dilution air is still used, and flue gas temperatures are high.

52 What We Should See In The Field
“B” Vent Outside Masonry “L” Vent

53 Drill test hole between the breech and the barometric damper
Barometric damper (“swinging door”) in an oil-fired warm air furnace vent. Drill test hole between the breech and the barometric damper Excessive draft should be corrected by the use of either a barometric damper or a modulating over-draft damper control system unless the natural venting system is sufficient. If a mechanical system is engaged, whether in the form of a draft inducer or an overdraft damper system, it must meet the operating requirement of the appliance. A slow or excessively fast system is not desirable. Both situations can be dangerous and lead to inefficient equipment operation. Verify that proper draft is easily maintained at each appliance outlet during cycling. Any system, whether operated by natural or mechanical draft, should be in balance within seconds of any change. Some draft controllers adjust the speed of a draft inducer in steps. These are slow-reacting and it can take more than 60 seconds to reach proper draft after a change. A true proportional-integral-derivative-based controller is always preferred. Verify that the heating appliances operate at the rated input and output. Sometimes a heating appliance manufacturer may reduce the gas flow rate as a remedy to improve the draft condition. However, make sure the owner is aware of this corrective action. After all, less output is worth less.

54 Why The Fuss About Venting Fan Assisted Gas Appliances?
11 Cu Ft flue gas for every 1 Cu Ft natural gas (Vs. 21 Cu Ft for 70% AFUE) Lower flue gas temperatures, (3500F) No dilution air (no draft hood) so gases are close to the dew point Water must stay in gaseous state to be removed from the building KEEP FLUE GAS AS WARM AS POSSIBLE

55 Tools & Equipment Used for Vent Inspection & Sizing
Tape measure Flashlight Mirror Combustion Analyzer Pressure Probe Temperature Probe Boroscope Digital Cameral NFPA manual 54, Natural Gas 58, LP Gas 31, Oil 211, Solid Fuels

56 Safety Inspection of the Venting System
Inside visual inspection General Safety Inspection Vent connections Internal flue inspection Outside visual inspection CAZ Test

57 Flue Safety Clearance to combustibles Spill switches Flue blockage
6” single wall pipe, gas 9” single wall pipe, oil 1” “B” vent, gas Single wall connectors must not pass through walls. Spill switches Flue blockage Condition of flue materials Draft under worst case conditions 1” Clearance? Fire stop?

58 Vent Connections Corrosion Pitch


60 Inspecting An Existing Application
Remove vent connector Inspect with mirror & light Is the vent straight or is there an offset Is there a liner present Are tiles cracked allowing flue gas to escape Blockage Examine termination from outside Cap Condition of flue

61 An appliance that produces soot is a cause for concern.
Auditor should call for clean and service.

62 Evidence of backdrafting

63 Hire a chimney sweep if necessary to drop a camera into the flue for a close inspection should you suspect a problem with the liner. Only 2’ or so on either end can be visually inspected with a mirror. Inspect for cracks allowing flue gasses to migrate to the area between the liner and the outer face material.

64 Unsafe vent

65 Check the chimney for accumulated debris.

66 Oil-fired boiler before cleaning – plugged with soot after several years without service.

67 Same boiler after cleaning

68 A number of cracks were found and light could be seen from the other side.
How might we fix this problem?

69 Be cognizant of the overall condition of the flue.

70 Transite Connector Must be Supported at Base

71 Termination Failure

72 B-vent exposed to the outdoors & not properly supported
Does not meet code ( ) Sizing tables 13.6 through are not to be used for “B” vent exposed to the outdoors below the roofline.

73 Draft assisted furnace, or only water heater left in flue?
Condensation bleed through

74 Condensation Damage

75 CAZ Test Place building in winter mode
Place all combustion appliances in pilot mode, or turn off Energize all exhaust fans Measure pressure difference between CAZ in relation to outdoors Open and close interior doors until the worst case draft condition is reached Must have draft to continue OD temp >800F, >-1 Pa or ”WC OD temp 300 – 800F, >-2.5 Pa or -.01”WC OD temp below 300F, >-5 Pa or -.02”WC

76 Vent Dampers Used to reduce off cycle losses Motorized Thermal
End switch safety Thermal Spill Switch

77 Thermal Vent Damper Bimetal petals warp open when heated


79 Vent Terminations Follow manufacturer instructions
Use NFPA guidelines if manufacturer instructions are not available

80 Category I Chimney termination:
A chimney shall extend at least 3 ft. above the highest point where it passes through a roof of a building and at least 2 ft. higher than any portion of a building within a horizontal distance of 10 ft.

81 Sealed Combustion Category IV
Follow manufacturer installation instructions.

82 Concentric Vent Category IV

83 Alternative Venting Many times you will not find a location to sidewall vent a powered draft system because of clearances that must be attained. Some of the typical requirements: · Vent terminal must be at least 1 foot from any door, window, or gravity inlet into the building.  · The double pipe (Example: The vent and air intake terminals must be at the same height and their center lines must be between 12 and 36 inches apart. Both terminals must be on the same wall) · All terminal bottoms must be 12 inches above normal snow line or no less than 12 inches above grade. (Note: it is often difficult to determine normal snow line) · 7 feet above public walkway · Do not install directly above windows or doors · The bottom of the vent terminal must be at least 3 feet above any forced air inlet located within 10 feet. · A horizontal distance of at least 4 feet between the vent terminal and gas meters, electric meters, regulators and relief equipment. Do not install vent terminal over this equipment dues to condensate. · Do not locate vent under decks. · Top of vent terminal must be at least 5 feet below eves, soffits, or overhangs. Maximum depth of overhang is 3 feet. · Vent terminal must be 6 feet from an inside corner. · Be aware that condensate may freeze and cause damage to structures nearby. · Install vent termination away from prevailing winds in excess of 40 MPH. · Air intake must not be near possible combustion air contaminants. 

84 Look for conditions that may affect health or safety of the occupants, the weatherization crew, and YOU. Dangerous vent, fire hazards, CO, fuel leaks, etc. Complete a Health and Safety Warning form if necessary.

85 Scary, home-made distribution system

86 REALLY scary homemade vent connector



89 Sizing Category I Vents
Use the appropriate NFPA manual 54 for Natural gas 58 for LP for Oil 211 for Solid fuels Find the appropriate chart One or more appliances? “B” Vent or masonry? “B” Connector or single wall? It is not the intent of this presentation to teach sizing, only to introduce the terminology and charts.

90 Using NFPA Sizing Charts
Height of flue From top of tallest appliance to the top of the flue termination Increasing the height increases the draw Horizontal distance to flue Used with single appliance application Increased horizontal run decreases draw Vertical connector height From the appliance breech to the point where flue gases combine Used with multiple appliances Elbows – Charts are listed with up to (2) 900 elbows in the vent


92 Problem #1 Single draft assisted appliance 50,000 BTU input rate
Total chimney height = 17’ Lateral distance = 3’ “B” vent and connector



95 Problem #2 2 category I appliances “B” vent with “B” connectors
50,000 BTU fan assisted furnace Connector rise = 2’ 30,000 BTU water heater Connector rise = 3’ “B” vent with “B” connectors Chimney height = 18’





100 Flexible Flue Liner Follow manufacturer sizing tables
Use NFPA sizing tables, but reduce capacity by 20% The masonry or original flue is used as a chase for the liner If a liner is installed, the remaining space around the liner can not be used to vent other appliances. More than one liner may be installed in the masonry chase “B” vent can not be used as a liner in this situation. Limited to flex liner.

101 Other Liner Materials “B” vent may be used as a liner
Drop down an inadequate or improperly sized flue Original flue must be straight. SS flexible liner

102 Review The height of a chimney is identified as:
If the chimney height falls between two columns in the NFPA chart, do you round up or down? For a single category I appliance installation, if the lateral distance falls between two value on the chart, do you round up or down? Can you use NFPA charts to size a flexible chimney liner? What is one advantage of using a flexible liner over “B” vent?

103 Vent Free Heaters NYS WAP Policy Operational Requirements
Oxygen Depletion Sensor Vent free introduced here because of the questions that have come up in class.

104 NYS WAP Policy WAP funds cannot be used to purchase or install any type of unvented or ventless combustion appliance including but not limited to unvented kerosene space heaters, unvented natural gas space heaters, unvented propane space heaters, unvented gas fireplaces, and unvented gas fireplace logs.

105 IAQ / Health & Safety Tests
Unvented Space Heaters: Educate the client about the potential danger of CO and fire from unvented space heaters. Explain that significant amounts of combustion products including water vapor and CO2 are produced.

106 Combustion Air Must supply combustion air while operating
Open window while operating Tucson instructions require defining the space as confined / unconfined Products of combustion remain in the conditioned space Must provide some measure of safety for oxygen depletion

107 Fresh Air Requirements Tucson Heater
Two permanent openings required. 1 sq. in. for every 1000 BTU/hr of all combined gas utilizing equipment in the confined space, but not less than 100 sq. in. Fresh Air Requirements Tucson Heater

108 Oxygen Depletion Sensor

109 If You Take Away Nothing Else
KEEP THE WATER IN A GASEOUS STATE WHILE IN THE FLUE Use “B”vent connectors on any new category I gas appliance installation Most masonry chimney’s will need a liner Never leave a water heater in a flue alone without ensuring it will vent

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