FREE HERS Rater PRACTICE EXAM
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Your Online HERS Rater Training CenterCAZ Depressurization LimitsWhat is an orphan natural draft water heater?
Orphan natural draft water heater (including outside chimneys)BPI Standard of -2 Pa limit, if more negative CAZ fails
Natural draft boiler or furnace commonly vented with water heaterBPI Standard of -3 Pa limit, if more negative CAZ fails
Remember, a natural draft furnace is going to be old and have NO draft fan in the AHU cabinet. Natural draft boiler or furnace with vent damper commonly vented with
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Mechanically-assisted draft boiler or furnace commonly vented with water
heater
BPI Standard of -5 Pa limit, if more negative CAZ fails.
Mechanically assisted means there is a small fan called a draft inducer, connected to the flue stack in the cabinet of the AHU.
Mechanically assisted means there is a small fan called a draft inducer, connected to the flue stack in the cabinet of the AHU.
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Mechanically-assisted draft boiler or furnace alone, or fan-assisted DHW
alone
BPI Standard of -15 Pa limit, if more negative CAZ fails.
If you are unsure if the furnace is fan assisted, follow the flue stack from into the AHU cabinet until it terminates. If it terminates at a small fan, it is mechanically assisted. If it terminates into open space, it is a natural draft.
If you are unsure if the furnace is fan assisted, follow the flue stack from into the AHU cabinet until it terminates. If it terminates at a small fan, it is mechanically assisted. If it terminates into open space, it is a natural draft.
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Chimney-top draft inducer (Exhausto-type or equivalent); High static pressure flame retention head oil burner; Direct-vented appliances/Sealed combustion appliances
BPI Standard of -15 Pa limit, if more negative CAZ fails
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