UPLIFT

Vent materials

Type leaving temperature, pressure, and whether it condenses. The list filters to what can take those conditions. The flue-material IOM is the number that limits the job — these are usual ceilings.

°F

°F

in

in. WC

Type a temperature, a pressure, or check condensing — the list filters as you go.

ProductTempPressureCheck

PVC

Category IV, only when leaving temperature stays under this.

149°FNeg. or pos. · typical 6 in

—

CPVC

Category IV, hotter condensing than PVC will take.

194°FNeg. or pos. · typical 6 in

—

Polypropylene

Category II and IV condensing vent.

230°F cont · 248°F intNeg. or pos. · typical 20 in

—

Stainless special gas vent

AL29-4C / 316L under UL 1738. Category II and IV.

Special gas vent is typically listed to 20 in. WC. Some products go higher; that has to be confirmed in the flue-material IOM.

550°FTypical 20 in · confirm IOM

—

Type B double-wall

Category I with a draft hood. Negative pressure only.

400°F cont · 550°F intNegative only

—

UL 1738 special gas vent

Listing · Category II and IV. PVC, CPVC, polypropylene, and stainless all sit under this listing. 550°F is the listing ceiling, not the rating of the PVC.

Special gas vent is typically listed to 20 in. WC. Some products go higher; that has to be confirmed in the flue-material IOM.

550°FTypical 20 in · confirm IOM

—

UL 103 factory-built chimney

Listing · Category I without a hood, and Category III when the chimney is listed for positive pressure. Continuous rating is 1,000°F.

Category III needs UL 103 listed for positive pressure, not special gas vent. Typical ceiling is 60 in. WC; some products go higher — confirm the flue-material IOM. Standard 103 is often negative only.

1,000°F cont · 1,400°F intTypical 60 in · confirm IOM

—

Generator / engine exhaust

Listing · Diesel and gas engines. Not a gas-appliance vent listing. Exhaust is far hotter than a boiler.

Generator / engine exhaust is typically listed to 60 in. WC. Some products go higher; that has to be confirmed in the flue-material IOM.

1,400°F cont · 1,800°F intTypical 60 in · confirm IOM

—

Typical ceilings, not a substitute for the appliance IOM or the flue-material IOM. A product sold under UL 1738 may be rated well below 550°F. Special gas vent typically warns at 20 in. WC; UL 103 and generator exhaust at 60 in. WC. Some manufacturers exceed those — confirm the flue-material IOM.

Category I–IV

Two questions: does the chimney pull or does the appliance push? Does it condense? That is the category.

Category
I

A non-condensing appliance operating under negative vent pressure. The chimney pulls. Gases stay above dew point from the appliance outlet to the termination.

Vent: Type B, masonry, or UL 103 chimney. On the Calculator pick Draft hood, or UL 103 if there is no hood.

Velocity

Size a round ID for a target velocity, or check velocity on a size you already have. Type ACFM at flue temperature.

acfm
fps

fps

°F
ft
Need
—
1200 fpm · A — ft²

Ductulator

Huebscher circular equivalent — the round ID with the same friction as the rectangle. Type either way. When the exact size falls between stock, the tool picks the even-inch size that still meets De.

in

inches

in

inches

Circular eq.
—″
Stock at or below
—
Nearest stock
—
Contraction k
0

Reducing k on this card is contraction onto a smaller stock ID, not the full velocity-head change.

Offset / transition

Two elbows make an offset. Type how far the centerline has to move. Optional round ID and rectangle give the minimum offset those elbows can make and the length of a round-to-rect transition.

in

inches

Elbows

in

optional

in

in

in

in

Slope CL
—″
Run
—″
Two elbows k
—
Min offset
—

Excess air / CO₂ / O₂

Convert a dry CO₂ or O₂ reading to excess air. 15% excess air is the default on the Calculator. Confirm with the appliance or burner manufacturer.

%
EA
46%
O₂
6.6%
M
1.10

Stoich CO₂ 11.7% · O₂ from EA is 6.6%

Quick size

Trial round diameter from input. W = 0.9 × I / 1000, then d = √(W / 16.189) at about 17 fps. Round 9.13″ up to 10″, then confirm on the Calculator.

Btu/h

Btu/h

default 0.90

W
—
lb/h
Trial d
—″
Nearest stock
—
Next size up
—

SCFM ↔ ACFM

SCFM is the volume as if the gas were sitting at 70°F. ACFM is the volume at the temperature in the flue. Size on ACFM. A generator should be typed as ACFM at exhaust temperature; if the sheet only listed SCFM, convert it here or switch Flow to scfm on the Calculator. 1,200 scfm at 900°F → about 3,080 acfm.

scfm

at 70°F

°F

°F

ACFM
—

in Hg ↔ in. WC

1 inch of mercury = 13.6087 inches of water. Draft is measured in inches WC.

in Hg
in WC

Theoretical draft

How much buoyancy a height and a temperature difference can make — no fittings, no friction. Shape does not change Dt. Real jobs need the Calculator.

ft
ft
°F
°F
Dt
—
in. WC
Dt / ft
—
Barometer 29.92 in Hg