Flue pipe turned downward

[Trent Tarter]

Gas furnace flue pipe turns downward before entering chimney. Unit has a combustion blower and is located in the crawlspace. I would think that this would not be allowed.

[Scott Patterson]

Gas furnace flue pipe turns downward before entering chimney. Unit has a combustion blower and is located in the crawlspace. I would think that this would not be allowed.

Needs to have a positive rise from start to end. Is there a metal flue pipe in that chimney as well?

[Trent Tarter]

That's what I thought just wanted to make shure, and yes the flue pipe goes all the way up chimney.

[A.D. Miller]

Gas furnace flue pipe turns downward before entering chimney. Unit has a combustion blower and is located in the crawlspace. I would think that this would not be allowed.

TT: From Duravent:


6. Slope. If the venting system contains
lateral (horizontal) components, they shall be
positioned so they have an upwards slope
away from the appliance of not less than
1/4-inch rise per foot of run. (Horizontal
vent installed in attics, unconditioned area, or

between floors have further restrictions, please
consult your local building codes for specific

limitations.)

From IRC:


G2427.10.8 (503.10.8) Slope. A vent connector shall be
installed without dips or sags and shall slope upward toward
the vent or chimney at least 1/4 inch per foot (21 mm/m).

Exception: Vent connectors attached to a mechanical draft
system installed in accordance with the manufacturers’
instructions.

The ideal chimney or vent configuration is a totally vertical
system, even though it is not always practical.
This section requires all portions of a chimney or vent
connector to rise vertically a minimum of a 1/4 inch per
each foot (21 mm/m) of its horizontal length. The connector
slope is intended to induce the flow of flue
gases using the natural buoyancy of the hot gases.
Connector slope can promote the priming of a cold
venting system and can partially compensate for short
connector vertical rise. Low points, dips and sags
could also trap condensate and accelerate corrosion
of the connector. The exception allows connectors
without slope where connected to mechanical draft
systems because the connector is on the negative
pressure (inlet) side of the exhauster and slope would
provide no benefit.

[John Arnold]

Isn't that single-wall? If so, not allowed in crawlspace, right?
It also doesn't appear to be properly supported.

[neal lewis]

Not to mention the clearance to combustible and being supported by a rock...

[Jerry Peck]

Isn't that single-wall? If so, not allowed in crawlspace, right?
It also doesn't appear to be properly supported.


Not to mention the clearance to combustible and being supported by a rock...

All the above, and ANY gravity flow vent is required to be sloped UPward at 1/4" per foot slope - as Aaron noted for Type B Gas Vent, applies to ALL gravity flow vents.

To my limited knowledge on power vents and direct vents, even those PVC vents are required to be vertical or horizontal sections sloped 1/4" per foot UPward.

[John Arnold]

...
To my limited knowledge on power vents and direct vents, even those PVC vents are required to be vertical or horizontal sections sloped 1/4" per foot UPward.

Yes, although for a different reason. It's to get the nasty condensate to drain back to the unit rather than drip outside on the family dog.

[Jerry Peck]

Yes, although for a different reason. It's to get the nasty condensate to drain back to the unit rather than drip outside on the family dog.

I was sure that was the reason (except the dog part ;) ), but I was not 100% sure that applicable to all, just r-e-a-l sure it was.

[Mike Schulz]

If that furnace has a fan assisted exhaust does the pitch still play in?

[Eric Barker]

With fan assisted there would be positive pressure in the vent - a vent that is not sealed/ designed against leakage.

[ed ferraioli]

The vent appears to be to long of a run with 2 elbow -- 30 ft max -each elbow acounts for 10 ft

[Jerry Peck]

The vent appears to be to long of a run with 2 elbow -- 30 ft max -each elbow acounts for 10 ft

Ed,

Do you have documentation which states the above?

[Vern Heiler]

Yes, although for a different reason. It's to get the nasty condensate to drain back to the unit rather than drip outside on the family dog.

Reason I have heard was to prevent ice blockage at the end of the vent opening. Probably not good for the dog either!

[Mike Schulz]

Reason I have heard was to prevent ice blockage at the end of the vent opening. Probably not good for the dog either!


Yes, although for a different reason. It's to get the nasty condensate to drain back to the unit rather than drip outside on the family dog.

And it runs back to the unit into a condensate pump or gravity 3/4 pvc and plumbed back outside again for that dog........... :D

[Bob Harper]

Cat IV is usually listed with the vent pitched to drain back towards the appliance. Pitching it towards the termination invited ice blockages as does a flat spot. On long horizontal runs in cold regions, this can really become a problem.

Actually, a fan assisted cat. I gas furnace is still considered negative vent pressure venting. Sure, when it first cycles on there is a short term pressurization of the portion of the vent closest to the appliance collar. But, after a minute, there *should* be enough heat in the stack to generate lift and create a draft or neg. vent pressure. That's why single walled connector and B-vent as still approved with these appliances. The joke is, these appliances are tested with a 5ft vent in the lab.

If you have leaks in pvc venting, you'll usually see a divot in the concrete where the concentrated acidic condensate is eating up the concrete floor. You can also test joints with a chemical smoke puffer and combustion analyzer.

To the pics from the OP: why didn't the installer punch through the right hand side of this chimney higher up, use B-vent for a 1" clearance with proper slope and req. in unconditioned space, properly supported? I know, rhetorical question.....

Trent, I'd be careful with your terminology. A 'combustion blower' might describe a positive pressure combustion chamber. FYI, you cannot power vent out Cat I gas & oil but you can power suck it out at the wall to maintain negative vent pressure.

Bob

[Mike Schulz]

FYI, you cannot power vent out Cat I gas & oil but you can power suck it out at the wall to maintain negative vent pressure.

Had one on mine that was mounted to suck it out at the foundation wall made by Field Controls. Never gave a thought why it was that way. Good post Bob.... Thanks