Orphan water heater

[Ponyboy]

Below is a picture of an orphanned water heater flue (4") connected to the original metal exhaust flue (12"). The original flue was sized for two gas furnaces and the gas water heater. The new gas furnaces are direct vent units. The flue vent is three stories tall on this house. I found no evidence of any backdrafting and the furnace room has a good combustion air supply. Any problem to report?

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[hausdok]

Hi Brad,

How long has that been configured this way? It might be working fine now, while the weather isn't too cold, but I'm skeptical about how it will perform this winter once it's trying to make a large slug of cold air. If they have to shut that water heater down for any reason in cold weather and then try to restart it, it's going to want to use the path of least resistance which is going to be back into the house via the draft diverter.

Also, right now there's liable to be a whole lot of condensation occurring in that large flue pipe that's draining to the bottom of that pipe and that's liable to eat a hole through that bottom elbow on the other side of the wall.

It seems like it would have made more sense to have run that 4" vent right up through the 12" vent and to have used a thimble on both ends to create a double-double-walled vent that would keep those gases nice and warm and buoyant for that three story trip to the outdoors.

ONE TEAM - ONE FIGHT!!!

Mike

[kurt]

Does the 7 times rule apply with a single appliance on a single flue?

If it does, the largest flue diameter for a 4" flue is 10".

Of course, that's what Chicago says; I'd have to check the outlander codes to know what's required in your area.

[Tom Raymond]

Does the 7 times rule apply with a single appliance on a single flue?

If it does, the largest flue diameter for a 4" flue is 10".

Of course, that's what Chicago says; I'd have to check the outlander codes to know what's required in your area.

Can you 'splain this rule please?

Tom

[kurt]

I just answered my own question by looking it up.......

When two or more appliances are connected to a chimney, the flow area of the largest section of that chimney cannot exceed seven times the smallest flue collar area, or the draft hood outlet area, unless designed with approved engineering methods.

Don't know if that explains it, but basically, it's the means for calculating the maximum flue size for multistory venting.