[Greenbuilding] venting a gas water heater into ABS plumbing?

[Reuben Deumling]

Bill,
that is quite an impressive list you've assembled of reasons not to do
this. You make several interesting points, and I appreciate the time
you took to respond. I concur on the issue of potentially igniting the
sewer gas, though I still don't know what the chances of this would
be. As for the remaining reasons you list, I'm not sure I'd see things
quite as you do. Perhaps it is due to my contradictory nature, or my
nonstandard approach to household technologies.

On Sun, May 11, 2008 at 12:20 PM, William R Bloom <wbloom at unm.edu> wrote:
...
> This is one perforation I would think you would want to go ahead and make.
>  First, gas water heaters are historically one of the most inefficient
> appliances in your house.  The flue will heat significantly and you do not
> want to introduce heat to ABS.  The polymer is not made to carry heated
> liquid, gas, anything.
Well my 60+ yr old water heater has an external flue and is extremely
efficient. For most of the year I don't even use the burner but let
the pilot light heat the water. I also use a damper (see
<http://tinyurl.com/6xartw>). As for hot liquids touching ABS, my
drainwater can get up to 110F (I'm assuming those who design and
certify this pipe count on even higher temperatures), whereas I've
measured the flue gas temperature near the top of the water heater as
only about 95F. Am I missing something?

> Second, there is no building code I know of that
> will approve such an installation.  Install without a permit and you might
> live with it for a while, but try to sell the house and a building inspector
> will have you retrofitting it.
This strikes me as a funny if all too familiar way to make decisions
about one's domicile. Most everything else I've done (or plan to do)
to my house is likely to (I am told) similarly hurt my chances at
selling it, but I don't ever plan to so maybe it won't matter. This
difference in attitude toward being present in one's house reminds me
of Ivan Illich's distinction between a resident and someone who
dwells:
"To dwell is human. Wild beasts have nests, cattle have stables,
carriages fit into sheds, and there are garages for automobiles. Only
humans can dwell. To dwell is an art.... To put the question, 'where
do you live?' is to ask for the place where your daily existence gives
shape to the world. Just tell me how you dwell and I will tell you who
you are.... To dwell then meant to inhabit one's own traces, to let
daily life write the webs and knots of one's biography into the
landscape....Dwellings were never completed before occupancy, in
contrast to the contemporary commodity, which decays from the day it
is ready to use.
The contemporary consumer of residence space lives topologically in
another world. The resident has lost much of his power to dwell. The
necessity to sleep under a roof for him has been transmogrified into a
culturally defined need. The liberty to dwell has become insignificant
for him. He needs the right to claim a certain number of square feet
in built-up space. ...He goes through life without leaving a trace.
The marks he leaves are considered dents--wear and tear. What he does
leave behind him will be removed as garbage. From commons for dwelling
the environment has been redefined as a resource for the production of
garages for people, commodities and cars. Housing provides cubicles in
which residents are housed. ... Those who insist now on their liberty
to dwell on their own are either very well off or treated as
deviants." (excerpted from "Dwelling," Address to Royal Institute of
British Architects, 1984)

As for building codes, you are undoubtedly correct.

> Third is the chance (probably slim) that a
> carbon heated glowing particle could rise from the waterheater gas burner
> and ignite sewer gas in the vent system.
This is my concern, but I'd be curious if anyone had thoughts on the
likelihood of this occurring. As in, can this conceivably occur at
all? Although I wish it were a wood fired water heater, mine, alas,
uses natural gas--a pretty clean burning combustion appliance I dare
say. I can't think of anything that would introduce a particle into
this system which could then act in the way you imagine.

 Fourth, most DWV waste vents
> typically terminate vertically on the roof without a cap or other
> termination device.  As such, rain can come down and doesn't cause a problem
> in a waste system, but will in your waterheater combustion system. You could
> cap it, but then be in risk of a violation of the plumbing code as vents
> cannot be restricted or capped.
I don't follow your logic. If I connect my water heater vent pipe
laterally with the vertical vent stack that passes through my roof,
say using an upside down 2" ABS wye, my water heater isn't going to
come in contact with any more moisture, or any more directly with it,
by this venting route than by any other I can think of.

> Lastly, I can't think of a galvanized flue
> to ABS fitting that you could use to tie the two together and hope that they
> would be gas-tight without using a rubber fitting also subject to heat.
Most (if not all) water heater flues are open to the atmosphere where
they connect to the water heater. If I were so inclined I could reach
my hand up into the path of the flue gas right now. I therefore don't
see why a tight fit would be required or even helpful.

Reuben Deumling