• APPENDIXT
    RECOMMENDED PROCEDURE FOR WORST-CASE TESTING
    OF ATMOSPHERIC VENTING SYSTEMS UNDER
    N1102.4 OR N1105 CONDITIONS ≤ 5ACH50

    (This appendix is informative and is not part of the code.)

    SECTIONT101
    SCOPE

    T101.1 General.

    This appendix is intended to provide guidelines for worst-case testing of atmospheric venting systems. Worst-case testing is recommended to identify problems that weaken draft and restrict combustion air.

    SECTIONT202
    GENERAL DEFINITIONS

    COMBUSTION APPLIANCE ZONE (CAZ). A contiguous air volume within a building that contains a Category I or II atmospherically vented appliance or a Category III or IV direct-vent or integral vent appliance drawing combustion air from inside the building or dwelling unit. The CAZ includes, but is not limited to, a mechanical closet, a mechanical room or the main body of a house or dwelling unit.

    DRAFT. The pressure difference existing between the appliance or any component part and the atmosphere that causes a continuous flow of air and products of combustion through the gas passages of the appliance to the atmosphere.

    Mechanical or induced draft. The pressure difference created by the action of a fan, blower or ejector that is located between the appliance and the chimney or vent termination.

    Natural draft. The pressure difference created by a vent or chimney because of its height and the temperature difference between the flue gases and the atmosphere.

    SPILLAGE. Combustion gases emerging from an appliance or venting system into the combustion appliance zone during burner operation.

    SECTIONT301
    TESTING PROCEDURE

    T301.1 Worst-case testing of atmospheric venting systems.

    Buildings or dwelling units containing a Category I or II atmospherically vented appliance; or a Category III or IV direct-vent or integral vent appliance drawing combustion air from inside of the building or dwelling unit, shall have the Combustion Appliance Zone (CAZ) tested for spillage, acceptable draft and carbon monoxide (CO) in accordance with this Section. Where required by the code official, testing shall be conducted by an approved third party. A written report of the results of the test shall be signed by the party conducting the test and provided to the code official. Testing shall be performed at any time after creation of all penetrations of the building thermal envelope and prior to final inspection.

    Exception: Buildings or dwelling units containing only Category III or IV direct-vent or integral vent appliances that do not draw combustion air from inside of the building or dwelling unit.

    The enumerated test procedure as follows shall be complied with during testing:

    1. 1.Set combustion appliances to the pilot setting or turn off the service disconnects for combustion appliances. Close exterior doors and windows and the fireplace damper. With the building or dwelling unit in this configuration, measure and record the baseline ambient pressure inside the building or dwelling unit CAZ. Compare the baseline ambient pressure of the CAZ to that of the outside ambient pressure and record the difference (Pa).

    2. 2.Establish worst case by turning on the clothes dryer and all exhaust fans. Close interior doors that make the CAZ pressure more negative. Turn on the air handler, where present, and leave on if, as a result, the pressure in the CAZ becomes more negative. Check interior door positions again, closing only the interior doors that make the CAZ pressure more negative. Measure net change in pressure from the CAZ to outdoor ambient pressure, correcting for the base ambient pressure inside the home. Record “worst case depressurization” pressure and compare to Table T301.1(1).

      Where CAZ depressurization limits are exceeded under worst-case conditions in accordance with Table T301.1(1), additional combustion air shall be provided or other modifications to building air-leakage performance or exhaust appliances such that depressurization is brought within the limits prescribed in Table T301.1(1).

    3. 3.Measure worst-case spillage, acceptable draft and carbon monoxide (CO) by firing the fuel-fired appliance with the smallest Btu capacity first.

      1. a.Test for spillage at the draft diverter with a mirror or smoke puffer. An appliance that continues to spill flue gases for more than 60 seconds fails the spillage test.

      2. b.Test for CO measuring undiluted flue gases in the throat or flue of the appliance using a digital gauge in parts per million (ppm) at the 10-minute mark. Record CO ppm readings to be compared with Table T301.1(3) upon completion of Step 4. Where the spillage test fails under worst case, go to Step 4.

      3. c.Where spillage ends within 60 seconds, test for acceptable draft in the connector not less than 1 foot (305 mm), but not more than 2 feet (610 mm) downstream of the draft diverter. Record draft pressure and compare to Table T301.1(2).

      4. d.Fire all other CONNECTED appliances simultaneously and test again at the draft diverter of each appliance for spillage, CO and acceptable draft using procedures 3a through 3c.

    4. 4.Measure spillage, acceptable draft, and carbon monoxide (CO) under natural conditions—without clothes dryer and exhaust fans on—in accordance with the procedure outlined in Step 3, measuring the net change in pressure from worst case condition in Step 3 to natural in the CAZ to confirm the worst case depressurization taken in Step 2. Repeat the process for each appliance, allowing each vent system to cool between tests.

    5. 5.Monitor indoor ambient CO in the breathing zone continuously during testing, and abort the test where indoor ambient CO exceeds 35 ppm by turning off the appliance, ventilating the space, and evacuating the building. The CO problem shall be corrected prior to completing combustion safety diagnostics.

    6. 6.Make recommendations based on test results and the retrofit action prescribed in Table T301.1(3).

    TABLE T301.1(1)

    CAZ DEPRESSURIZATION LIMITS

    VENTING CONDITIONLIMIT (Pa)
    Category I, atmospherically vented water heater−2.0
    Category I or II atmospherically vented boiler or furnace common vented with a Category I atmospherically vented water heater−3.0
    Category I or II atmospherically vented boiler or furnace, equipped with a flue damper, and common vented with a Category I atmospherically vented water heater−5.0
    Category I or II atmospherically vented boiler or furnace alone
    Category I or II atmospherically vented, fan-assisted boiler or furnace common vented with a Category I atmospherically vented water heater
    Decorative vented, gas appliance
    Power vented or induced-draft boiler or furnace alone, or fan-assisted water heater alone−15.0
    Category IV direct-vented appliances and sealed combustion appliances−50.0

    For SI: 6894.76 Pa = 1.0 psi.

    TABLE T301.1(2)

    ACCEPTABLE DRAFT TEST CORRECTION

    OUTSIDE TEMPERATURE (°F)MINIMUM DRAFT PRESSURE REQUIRED (Pa)
    < 10−2.5
    10 – 90(Outside Temperature ÷ 40) − 2.75
    > 90−0.5

    For SI: 6894.76 Pa = 1.0 psi.

    TABLE T301.1(3)

    ACCEPTABLE DRAFT TEST CORRECTION

    CARBON MONOXIDE LEVEL (ppm)AND ORSPILLAGE AND ACCEPTABLE DRAFT TEST RESULTSRETROFIT ACTION
    0 – 25andPassesProceed with work
    25 < × ≤ 100andPassesRecommend that CO problem be resolved
    25 < × ≤ 100andFails in worst case onlyRecommend an appliance service call and repairs to resolve the problem
    100 < × ≤ 400orFails under natural conditionsStop! Work shall not proceed until appliance is serviced and problem resolved
    > 400andPassesStop! Work shall not proceed until appliance is serviced and problem resolved
    > 400andFails under any conditionEmergency! Shut off fuel to appliance and call for service immediately
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