Concrete underslab return duct flooding

Posted by Larryboy on September 5, 2006, 3:45 pm

Help! I'm property chairman of a small church. One of our buildings
has a brick lined return air duct under the 1st floor concrete slab
that is flooding. I pumped out a foot of standing water from this
under slab duct last weekend. I spoke to a few old timers, who
remember pumping this duct out many years ago. Obviously they never
checked on the flooding again, until I noted the problem while
replacing some very old and very dirty metal mesh filters on this
system - I was washing off the coils, when I noted that the concrete
under slab duct was flooded with a foot of water. I have placed a sump
pump in the duct, but can only pump down to 1/8 inch, since there is no
sump pit. There is also a lot of mud that has settled out on the floor
of the duct, that I attempted to wash loose and pump out, but I can
only see a small portion of this 100 foot long duct. There is no sign
of any mold or other critters growing, and the water was pretty clear
before I stirred it up with the pump. I suspect this water is seeping
in between the concrete floor slab and the brick lined duct. This HVAC
system is run mainly on the weekends for church school and AA meetings,
etc. Question: what can I do to clean this water up and prevent it
from reoccurring?

Posted by Power's Mechanical on September 5, 2006, 6:09 pm

Larryboy wrote:

> Help! I'm property chairman of a small church. One of our buildings
> has a brick lined return air duct under the 1st floor concrete slab
> that is flooding. I pumped out a foot of standing water from this
> under slab duct last weekend. I spoke to a few old timers, who
> remember pumping this duct out many years ago. Obviously they never
> checked on the flooding again, until I noted the problem while
> replacing some very old and very dirty metal mesh filters on this
> system - I was washing off the coils, when I noted that the concrete
> under slab duct was flooded with a foot of water. I have placed a sump
> pump in the duct, but can only pump down to 1/8 inch, since there is no
> sump pit. There is also a lot of mud that has settled out on the floor
> of the duct, that I attempted to wash loose and pump out, but I can
> only see a small portion of this 100 foot long duct. There is no sign
> of any mold or other critters growing, and the water was pretty clear
> before I stirred it up with the pump. I suspect this water is seeping
> in between the concrete floor slab and the brick lined duct. This HVAC
> system is run mainly on the weekends for church school and AA meetings,
> etc. Question: what can I do to clean this water up and prevent it
> from reoccurring?

Fix or install drain tile around the building. Make sure the ground is
sloped away from the building so that rain water drains away from the
building. Find the source of the water and redirect it.

Posted by Stormin Mormon on September 5, 2006, 11:04 pm

Make sure the drain from the baptistry goes into the storm or sanitary
sewer, not the HVAC duct.

See if you can get Moses to part the waters in the duct. Would that be
a "Mini-Mo" to fit in there?

Hold a prayer meeting.

But first, do the gutters and grading thing like he said. And keep the
sump pump handy.

--

Christopher A. Young
You can't shout down a troll.
You have to starve them.
.

Fix or install drain tile around the building. Make sure the ground
is
sloped away from the building so that rain water drains away from the
building. Find the source of the water and redirect it.

Posted by JimL on September 6, 2006, 12:12 pm

wrote:

>Help! I'm property chairman of a small church. One of our buildings
>has a brick lined return air duct under the 1st floor concrete slab
>that is flooding. I pumped out a foot of standing water from this
>under slab duct last weekend. I spoke to a few old timers, who
>remember pumping this duct out many years ago. Obviously they never
>checked on the flooding again, until I noted the problem while
>replacing some very old and very dirty metal mesh filters on this
>system - I was washing off the coils, when I noted that the concrete
>under slab duct was flooded with a foot of water. I have placed a sump
>pump in the duct, but can only pump down to 1/8 inch, since there is no
>sump pit. There is also a lot of mud that has settled out on the floor
>of the duct, that I attempted to wash loose and pump out, but I can
>only see a small portion of this 100 foot long duct. There is no sign
>of any mold or other critters growing, and the water was pretty clear
>before I stirred it up with the pump. I suspect this water is seeping
>in between the concrete floor slab and the brick lined duct. This HVAC
>system is run mainly on the weekends for church school and AA meetings,
>etc. Question: what can I do to clean this water up and prevent it
>from reoccurring?

A jack hammer will remove a substantial part of a slab in no time at
all.

It will also let you cut a hole for a sump pump. I would choose a
position approximately half way in the run to put the sump pump and
hole.

Posted by Larryboy on September 7, 2006, 5:16 pm

Thanks for everyone's good advice. I have looked around the perimeter
of the building and found that someone in the past had attempted to put
in a cheap french drain system on one side of the building, but it is
sitting partially above ground now and obviously is no longer
effective. Looks like it's time for a shovel brigade party, new pipe
and a lot of gravel. The other side of the building was relandscaped
last year, so I didn't go poking about there yet - I need to notify
some ladies in the church before I go digging in the new shrub bed.
Regarding the last suggestion posted - I can't access the middle of the
duct to dig a sump pit, because this underslab concrete duct runs
directly beneath the long central hallway - perhaps a large indoor
fountain/baptismal font would cover it up? I've left the sump pump in
the duct return access for now and will pump out the water as needed.
We've had a wet summer, so that has made matters worse. Thanks again!

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