Chimney FundamentalsAnd Operation The Art of Venting Flue Gases Or How Not To Kill Your Client Presenter: Earl Hicks
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
NYS WAP Policy • Ensure safe elimination of flue gases from the building
BPI StandardsBuilding 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.
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 Chemical Reaction • CH4 + 4O2 + heat = CO2 + 2H2O + heat • Complete combustion • Natural gas • 1 Cu Ft of CH4 + 10 Cu Ft of air for complete combustion • 11 Cu Ft of flue gases
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.
Confined / Unconfined • Confined 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.
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
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
Solution • CAZ = 10’L X 14’W X 8’H • 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
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 54 184.108.40.206(1) • For fan-assisted appliances, consult NFPA 54 220.127.116.11(2)
Table 18.104.22.168(a) Natural Draft Appliances
Methods of Bringing In Combustion Air • Within the dwelling, from other zones • Ducted in horizontally from OD • Directly from OD above and or below
What is Draft • Negative pressure within a flue that pulls products of combustion out from the dwelling.
Factors That Affect Draft Pressure • Delta T, Indoors to Outdoors • Height of Vent • Interior Volume • Restrictions • Atmospheric Conditions • Pressure Imbalances in the CAZ
How Does A VentingSystem Work? Air Flow Combustion Gases
What is Considered Adequate Draft? • OD temp >800F, >-1 Pa or - .005”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.)
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
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
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 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 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 • Has been used to solve installation problems where no appropriate flue is available • Positive pressure requires joints in flue material to be sealed
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 I Vent MaterialsFound 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
Category I Vent Materialscont. • “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
Category I Vent Materialscont. • 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
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.
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
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.
93#(lbs) ~ 10 gallons • Million Btu = 100,000 Btu @ 10 Hrs run time • 10 Hr run time for natural gas = 10 gallons of water that must be removed from the flue.
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
Draft Hood Appliances • 1 Cu Ft CH4 + 10 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
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.
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: .2 hr x 25,000 Btu/hr = 5,000 Btu/cycle MASONRY CHIMNEY:A masonry chimney (block or brick + tile liner) requires about 4570 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 Btu/cycle @4,570Btu/ft = 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 Btu/cycle @ 90Btu/ft = 55 ft/cycle
After Weatherization with aNew 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 Btu/cycle @ 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 Btu/cycle @ 90Btu/ft = 15 ft/cycle
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
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 set @ 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.
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 13.2.2) • 1 ½ times the diameter of the connector in feet • 4” connector = 6’ maximum horizontal distance
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