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UPLIFT

Chimney draft calculation

ASHRAE chimney design method

Project

—

Location

—

Elevation

0 ft

Barometer

29.92 in Hg

System

Chimney draft

Listing

Draft hood

—

Incomplete

Da = Dt − Δp = 0.0000 − 0.0000

Available draft Da

—

in. WC

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Appliance schedule

TagMakeModelInputListing
B-1———Draft hood

Fuel

Natural gas

Input

0 MBH · Natural gas

Mass factor M

1.60 lb / 1,000 Btu

Combustion

Hood dilution included · 5.3% CO₂

ACFM

—

SCFM

—

Mass flow

—

ACFM is volume at 350°F. SCFM is the same mass at 70°F. The flue is sized on ACFM.

Design data

Ambient

60°F

Flue gas temp

350°F

Mean temperature

350°F

Temperature factor Cu

1.00

Vertical rise H

0 ft

Centerline length L

0 ft

Friction F

0.40

Pass criterion

Da ≥ 0

Density

—

Total k

—

Diameter at 17 fps

—

Fitting schedule

No fittings entered.

Governing equations

  • W = I × M / 1000
  • ACFM = W / (ρ × 60)
  • ACFM = SCFM × (460 + T) / 530 (T in °F; 530 = 70 + 460)
  • EA% = 100 (CO₂max / CO₂ − 1) O₂ ≈ 20.9 × EA / (100 + EA)
  • ρ = 1.325 B / Tm Tm = Tamb + Cu (Texit − Tamb)
  • Dt = 0.2554 B H (1/To − 1/Tm) combustion air Dt = 0
  • V = ACFM / (A × 60) Vh = ρ V² / (2 g × 5.202) Δp = k × Vh
  • k_friction = F L / D F = 0.40 (ID ≤ 18″) or 0.30
  • Draft hood: Da = Dt − Δp. Pass if Da ≥ 0.
  • ASHRAE fitting k, pressed / long-radius: 90° = 0.40. Mitered 90° ≈ 0.75 — enter under Other k.

Remarks

  • Draft hood: size so losses stay at or under theoretical draft. Draft is included.