Exterior mounted B-vents

[Ponyboy]

Two gas appliances (natural draft water heater & Type I gas furnace) installed in the basement are using exterior mounted B-vents. The vents are both about 30 feet tall. Based on the venting table I have this installation is acceptable. But at a recent seminar Doug Hansen stated this installation can casue problems with drafting. Can't remember exactly what Doug said so looking for some advice?

Brad

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[Mike Lamb]

From Amerivent Installation & Assembly Instructions:

2. AmeriVent Gas Vent is suitable for installation inside or

outside. However,the sizing tables in NFPA 54 are for

vents not exposed to the outdoors below the roof line.

Outside vents could reduce venting action; therefore,

such installations are not recommended. In the event

outside venting is necessary, vents should be sized as

close to maximum capacity as possible. Whenever

possible, outside vents should be enclosed inside a

chase that maintains the minimum one (1) inch

clearance to combustibles. Appliances served by an

outside vent must have an adequate air supply to

balance inside and outside air pressure to reduce the

possibility of reverse venting action.

I'm sure outside temps would have a lot to do with this.

[carle3]

I have not heard Doug's presentation but I would think the concern in cold weather climates is that the majority of the pipe is not tempered in a warm air cavity. This would allow the gases to condense before they get out the termination. Result acidic moisture eating at the walls of the pipe.

[Jim Katen]

Originally posted by Ponyboy

Two gas appliances (natural draft water heater & Type I gas furnace) installed in the basement are using exterior mounted B-vents. The vents are both about 30 feet tall. Based on the venting table I have this installation is acceptable. But at a recent seminar Doug Hansen stated this installation can casue problems with drafting. Can't remember exactly what Doug said so looking for some advice?

Brad

2006 IRC, section G2428.2.9 Chimney and vent locations. Tables G2428.2(1) and G2428.2(2) shall only be used for chimneys and vents not exposed to the outdoors below the roof line . . . .

- Jim Katen, Oregon

[Darren]

Geez;

Why didn't they just install direct vent units?

[Ponyboy]

Originally posted by Darren

Geez;

Why didn't they just install direct vent units?

Well, that is the million dollar question!?!?

I have another twist to this installation. Just was at the house with an HVCA consultant and he noted that the air return which the furnace is sitting on is built of wood with no sealed joints. Does anybody know if this is allowed? If not it would be great to add to my case of installing a new direct vent furnace.

[Bain]

High efficiency furnaces are more expensive than the 80%ers. Peeps can't always afford the best.

The set-up in the photo was disallowed for a few years around here, but it's now permitted again. The muni inspectors are told to treat the things like chimney flues. As long as the vent is double-walled, no problem.

I'm not sure it would be prudent to tell your client the existing furnace must be replaced with an upgrade. That doesn't seem fair to the seller.

As for the unsealed joints in the return trunk-duct, a ten dollar tub of duct mastic would remedy the issue.

[hausdok]

Hi Brad,

Exactly what is the vent in the foreground supposed to be; their fresh air intake to that area? Where is the water heater you mentioned above in relation to this furnace?

OT - OF!!!

M.