Questar Gas - Good Practices for Gas Piping and Appliance ...

DAMPER - A valve or plate for regulating draft.
DECATHERM - Equal to 10 therms or 1,000,000 Btu.
DECORATIVE APPLIANCE - Vented appliance whose primary
function is the appearance of the flame.
DEMAND - The maximum amounts of gas required per unit of
time, usually expressed in cubic feet per hour or Btu per hour,
required for the operation of the appliance or appliances supplied.
DILUTION AIR - Air which enters a draft hood and mixes with
the flue gases.
DIRECT VENT APPLIANCE - Appliances which are so
constructed and installed that all air for combustion is derived from
the outside atmosphere and all flue gases are discharged to the
outside atmosphere.
DRAFT HOOD - A device built into an appliance, or made a part
of the flue or vent connector from an appliance, which is designed
to: (1) ensure the ready escape of the products of combustion in
the event of no draft, back draft, or blockage beyond the draft
hood; (2) prevent a back draft from entering the appliance, and;
(3) neutralize the effect of stack action of the vent or chimney
upon the operation of the appliance.
ELEVATED PRESSURE - Pressure more than fourteen (14) inches
of water column.
EQUIVALENT HYDRAULIC DIAMETER (EHD) - Measurement
of the hydraulic efficiency between different tubing sizes. The
higher the number EHD, the greater the capacity of tubing. This
number is used when sizing corrugated stainless steel tubing
(CSST).
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