Underground flue pipe

[Ken Amelin]

This one got my curiosity.

It was in a home I inspected yesterday, built in 1971.

The FHA metal flue pipe enters the foundation approximately 6 feet on the left of the chimney. The other side of the concrete foundation is the garage floor slab.

Since there are no indications otherwise, I suspect that the flue pipe was run through the foundation wall, takes a 90 degree right turn under the garage floor slab (most likely buried in soil) then connects to a chimney flue somewhere under the slab.

My report says that this is a potential safety hazard. Metal flue pipe in contact with soil can corrode. Condition of concealed piping is unknown. Further inspection advised for your safety.

Does anyone know if this is a current code violation? Can flue pipe be routed under ground? Should I have recommended that it be disconnected and re-routed?

[Jerry Peck]

Not good.

Not only is it possibly rusted through in places, the soil around it would act as a good heat sink, not allowing the flue to heat up with the flue gases, possibly causing draft problems.

[John Kogel]

We would expect that fireplace on the right of the pic to have a double flue, so the furnace would vent into the side of the masonry chimney. Hard to know when it's all covered up, but that would make more sense than burying the metal pipe in dirt under a garage floor.

[Bob Harper]

The metal vent must be listed and installed to the listing. I've never seen any listed for direct bury in soil but I have seen them all say do not cover such as with insulation because it should be visible for inspection unless it is contained within the framed vertical chase with proper clearances and support.

No way to inspect or replace
high probability for damage or corrosion
no way to clean out base
cold condensing vent
may be too long horizontal offset
is it flat or pitched?
If the soil shifts and separates the pipe, you wouldn't know it

recommend alternative venting such as power vent at wall/ roof or replace equipment with CAT IV

Not sure why a fireplace would have two flues....?

[John Kogel]

Not sure why a fireplace would have two flues....?Thanks Bob. By two flues, I meant, in a typical older house set up for central heating, the fireplace upstairs has a flue and there is a second flue in the masonry open to the basement. Is there a name for the total masonry package which includes the fireplace(s) and additional flues?

[Bob Harper]

LOL. Reason I asked is the masons in my hometown love to build fireplaces with twin hole chimneys: two 8x13s side by side.

One builder claimed cold air went down one stack and smoke up the other. Smart smoke....

You can have one chimney with multiple flues and multiple fireplaces. The flues are the holes and the fireplaces are masonry appliances. All chimneys have at least one flue by definition and all fireplaces have a chimney with one flue for the Fp.
HTH,

[Nick Ostrowski]

LOL. Reason I asked is the masons in my hometown love to build fireplaces with twin hole chimneys: two 8x13s side by side.

One builder claimed cold air went down one stack and smoke up the other. Smart smoke....

You can have one chimney with multiple flues and multiple fireplaces. The flues are the holes and the fireplaces are masonry appliances. All chimneys have at least one flue by definition and all fireplaces have a chimney with one flue for the Fp.
HTH,

A Drexel Hill special Bob? ;)

I saw this same setup in a DH house. A real head scratcher.

[Bob Harper]

Naw Nick, that was back in SC. What I do see around here is the heater flue exposed in the fireplace smoke chamber. Usually cracked leaking into house.

Yeah, those double barrelled shotguns were a PIA to vent a woodstove insert into esp. when the stove required an 8" round ovalized. Evevy single one I busted flue tile out on was nothing but a collection of loosely stacked bricks without mortar and always smoke stained meaning the flues leaked.

How have you been? We oughta do lunch sometime.

[Tom Kio]

LOL. Reason I asked is the masons in my hometown love to build fireplaces with twin hole chimneys: two 8x13s side by side.

One builder claimed cold air went down one stack and smoke up the other. Smart smoke....

You can have one chimney with multiple flues and multiple fireplaces. The flues are the holes and the fireplaces are masonry appliances. All chimneys have at least one flue by definition and all fireplaces have a chimney with one flue for the Fp.
HTH,
Year, good idea.