Water Heater Flue Point of Entry

[hausdok]

Hi All,

Trying to remember. I can't find the rule that says a water heater vent has to enter a shared vent higher than the furnace vent. Or was it the smaller has to enter the stack first? Fuzzy on the exact wording.

Got a water heater and furnace sharing the same flue - a steel liner running up through the tile lining of a masonry stack. The water heater connector makes its connection to the flue above the furnace connector but the furnace connector joins the shared flue closer to the masonry stack with a Tee.

In the photo below, the connector entering the B vent from the bottom is the furnace connector and the one entering at the upper right is the water heater vent connector.

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I found evidence that spillage at the water heater draft hood is so heavy that the plastic insulators/grommets (whatever the hell you'd like to call them) around the hot and cold pipes, as well as the one around the top of the anode rod, are melted all to hell. There's plenty of combustion air to the room. and there aren't any fans or dryers or anything like that nearby....although, just around the corner from the louvered door in the room where the combustion air comes from is a fireplace fitted with a gas log set with the damper permanently clamped open.

Here's the melted plastic doohickeys:

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I'm thinking that if this water heater connection had been on the other side of this furnace connection closer to the stack, and the furnace connection had been made with a Wye and not a Tee, the spillage might not have been an issue.

What say ye? Anyone remember that rule I'm trying to remember or is my brain playing tricks on me again?

ONE TEAM - ONE FIGHT!!!

Mike

[patt]

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And

UMC 2009

802.10.4.2 Where two (2) or more vent connectors

enter a common gas vent, chimney flue, or single?

wall metal pipe, the smaller connector shall enter at

the highest level consistent with the available head?

room or clearance to combustible material. [NFPA

54:12.11.4.1]

IRC 2009

G2427.10.4 (503.10.4) Two or more appliances connected to a

single vent or chimney. Where two or more vent connectors enter

a common gas vent, chimney flue, or single-wall metal pipe, the smaller

connector shall enter at the highest level consistent with the available

headroom or clearance to combustible material. ...

IMC 2009

803.7 Connectors serving two or more appliances. Where

two or more connectors enter a common vent or chimney,

the smaller connector shall enter at the highest level consistent

with available headroom or clearance to combustible material.

[Brandon Whitmore]

It's wrong. (as indicated by Peter's posting)

It doesn't really seem to matter which ties in first with that configuration. Kick the water heater up, and then turn on an induced draft furnace, and you'll likely find heavy spillage at the draft hood.

[David Meiland]

there aren't any fans or dryers or anything like that nearby

There's a helluva big fan right there in the room, in the furnace itself. If there are large supply duct leaks in the system, and the returns are tight, the blower could be depressurizing the house enough to suck flue gas down and out the draft hood on the water heater.

The house in Olympia where I did some of my BPI training was a great example of this. The furnace sucked flame right out of the water heater and scorched the vinyl floor.

[OCallaghan]

Looking at the photo, the furnace discharge vent and the the combined vent are the same size (5"?). At the minimum, a combined vents needs to be one size larger than the larger discharge vent. This isn't the likely the issue if the furnace btu's require a size smaller vent, say 4". This disign is an approved layout if all other criteria are met...Heart and Cooley has charts and details on their sight.

You're better to look 'em up than me try to explain the many details.

http://www.hartandcooley.com/tools/down ... 9094a11d63

PAGE 15...and ...Fig 4-D (pg-9)

If the link is inop. Go the H&C/ Download literature/ Vent & Chimney/ H&C Literature/ Sizing Guide...

[Marc]

Excellent source of info on gas vents!

Marc

[Brandon Whitmore]

Hi OCallaghan,

Looking at the photo, the furnace discharge vent and the the combined vent are the same size (5"?).

I assume you mean vent connector & common vent (helps to keep things easy to understand when same terminology is used).

I agree that the furnace vent connector and common vent appear to be the same size, as is allowed

At the minimum, a combined vents needs to be one size larger than the larger discharge vent.

Not according to Hart& Cooley: see quote below found here

CAUTION. Regardless of the COMMON VENT size

determined by the above procedure, the vent MUST be

at least as large as the largest connector. If more than

one connector is this same size, then use a COMMON

VENT one size larger.

PS: See figure 6 that shows the smaller btu vent connector tied in after (above) the higher btu rated piece of equip.....

[Jim Baird]

The water heater noted in my "creative venting post" had obviously leaked some of its hot effluent so that plastic doohickeys were melted, as in Mike O's pics.

Reason, tho, I think, is clogged vent due to dryer lint.

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[Hearthman]

2009 IRC 2427.10.3.4 allows manifolding such as shown here. Even in the following section, where it discusses "the smaller connector shall enter at the highest level consistent with the available headroom or clearance to combustibles", this applies only to where and if the multiple connectors enter a "common gas vent, chimney flue or single walled connector."

In other words, if you have two holes in the chimney, the smaller goes on top. Otherwise, if you create a manifold, such as shown here, it is allowed as long as they use B-vent. Even if they had used single walled connector, they could manifold it as long as the smaller enters the manifold higher than the larger while respecting clearances and getting the max. vertical vent rise.

What the code is after is to get the max. vent rise off the appliance to reduce the chances of spillage. All this stuff about fumes blowing out the smaller if below or the larger overpowering the smaller is all urban legend BS. Refer to the Code Commentary.