When you are asked "wye" not?

**Michael Thomas** · 06-10-2008, 04:23 PM

Where can I find a good discussion of the specification of "wyes" as opposed to "tees" for gas appliance venting? I want to cover every possible base on this little beauty:

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**Matt Fellman** · 06-11-2008, 08:15 AM

I can't help with your question but something I do in that scenario is line up the vent pipe with the chimney's mortar joints in your photo (assuming they're level) and it gives a great point of reference to see just how bad the lack of any slope is.

James Duffin · 06-11-2008, 09:27 AM

The main reason I see to use a wye over a tee is to cut down on the amount of restriction in the vent system. Below is an excerpt from the Duravent manual.

COMPENSATING FOR EXTRA ELBOWS

For single appliance venting configurations, Tables I and II,
a zero lateral length is assumed to have no elbows in the
vent system. For vent configurations that do have lateral
lengths, the capacities shown in the tables assume that the
vent system has the equivalent of two 90° elbows, which
may be located at any position in the vent system. The
system could have:
A. Two 90° elbows.
B. One 90° elbow and one tee.
C. Four 45° elbows.
D. Two 45° elbows and one tee.
When more than two 90° elbows are required in the
venting system, the maximum capacity listed in the venting
tables should be reduced by 10% (0.90 x maximum listed
capacity) for each additional 90° elbow, or equivalent.
Please note that 90° elbows are only allowed in the same
space as the appliance and are not permitted above the
ceiling.

Figure 54.

Length of Lateral
(L)
Total Vent
Height (H)