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I know it's a no-go; I'm looking for the rule.


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Hi all,

Just had this. Scenario - a small uninsulated mechanical room attached to the end of a house. Inside is a boiler supplying hot water to hydronic baseboard convectors and a radiant floor heat system. The exhaust is a single-walled pipe that passes out through the plywood wall on one side, extends a couple of feet, turns downward and then ends.

I could be wrong, but I suspect that the vent used to turn upward and had another section attached that's long-since been lost to the ages. The current homeowner purchased the house this way and has no idea if there used to be a connected vent.

OK, so the vent needs six inches of clearance. That's easy. But since it's not venting into a dedicated stack I believe that vent should be a double-walled type because using a single-walled metal vent on the side of a house is going to end up with a lot of condensation occurring in the vent.

Currently working on this report and have a short deadline. would like to not have to spend a lot of time digging around for the rules that state that the vent needs to be double-walled material and needs to extend up the side of the house and then clear the house/roof. If anyone can help me save a little time and has those cites handier than I do, please post them here.

Much obliged to anyone that has 'em handy.



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Assuming it's gas:

G2427.6.3 (503.6.4) Gas vent termination. A gas vent

shall terminate in accordance with one of the following:

1. Gas vents that are 12 inches (305 mm) or less in size

and located not less than 8 feet (2438 mm) from a vertical

wall or similar obstruction shall terminate above

the roof in accordance with Figure G2427.6.3.

G2427.6.4 (503.6.5) Minimum height. A Type B or L gas

vent shall terminate at least 5 feet (1524 mm) in vertical

height above the highest connected appliance draft hoodor

flue collar. A Type B-W gas vent shall terminate at least 12

feet (3658 mm) in vertical height above the bottom of the

wall furnace.

G2427.6.5 (503.6.6) Roof terminations. Gas vents shall

extend through the roof flashing, roofjack or roof thimble

and terminate with a listed cap or listed roof assembly.

G2427.6.7 (503.6.8) Exterior wall penetrations. A gas

vent extending through an exterior wall shall not terminate

adjacent to the wall or below eaves or parapets, except as

provided in Sections G2427.2.1 and G2427.3.3. (Those have to do with mechanical venting, not natural draft.)

G2427.7.2 (503.7.2) Cold climate. Uninsulated single-

wall metal pipe shall not be used outdoors for venting

appliances in regions where the 99-percent winter design

temperature is below 32?F (O?C).

G2427.7.3 (503.7.3) Termination. Single-wall metal pipe

shall terminate at least 5 feet (1524 mm) in vertical height

above the highest connected appliance draft hoodoutlet or

flue collar. Single-wall metal pipe shall extend at least 2 feet

(610 mm) above the highest point where it passes through a

roof of a building and at least 2 feet (610 mm) higher than

any portion of a building within a horizontal distance of 10

feet (3048 mm) (see Figure G2427.5.3). An approvedcap or

roof assembly shall be attached to the terminus of a single-

wall metal pipe (see also Section G2427.7.9, Item 3).

G2427.7.4 (503.7.4) Limitations of use. Single-wall metal

pipe shall be used only for runs directly from the space in

which the appliance is located through the roof or exterior

wall to the outdoor atmosphere.

G2427.7.6 (503.7.6) Installation. Single-wall metal pipe

shall not originate in any unoccupied attic or concealed

space and shall not pass through any attic, inside wall, concealed

space, or floor. The installation of a single-wall metal

pipe through an exterior combustible wall shall comply with

Section G2427.7.7. Single-wall metal pipe used for venting

an incinerator shall be exposed and readily examinable for

its full length and shall have suitable clearances maintained.

G2427.7.7 (503.7.7) Single-wall penetrations ofcombustible

walls. Single-wall metal pipe shall not pass through a

combustible exterior wall unless guarded at the point ofpassage

by a ventilated metal thimble not smaller than the following: blah, blah (I can cut & paste more, but I think you've got enough.)

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For Oil:

M1804.1 Type ofvent required. Appliances shall be provided

with a listed and labeled venting system as set forth in Table


TABLE M1804.1



Type L oil vents -Oil-burning appliances listed and

labeled for venting with Type L vents

Pellet vents- Pellet fuel-burning appliances listed and

labeled for use with pellet vents

M1803.3.1 . . . Connectors for oil-fired appliances listedand

labeledfor Type L vents, passing through walls or partitions

shall be in accordance with the following:

2. Single-wall metal pipe shall be guarded by a ventilated

metal thimble not less than 4 inches (102 mm)

larger in diameter than the vent connector. A minimum

6 inches (152 mm) of clearance shall be maintained

between the thimble and combustibles.

M1804.2.3 Natural draft appliances. Vents for natural

draft appliances shall terminate at least 5 feet (1524 mm)

above the highest connected appliance outlet, and natural

draft gas vents serving wall furnaces shall terminate at an

elevation at least 12 feet (3658 mm) above the bottom of the

furnace .

I can't find anything that would prohibit a single wall vent connector in an unheated space for an oil appliance.

Bottom line is that they can't use single-wall as the vent, they can only use it as the vent connector.

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