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Condensate drain into sink vent?

CeltsFan's picture

We're relocating our furnace/AC unit to the attic, which is also becoming conditioned space.


The HVAC guy wants to tie into the vent for the kitchen sink as the drain line. He says they "do it all the time". Is this a concern? Theoretically, it wouldn't matter, but I just don't know if when they are running PVC pipe for a vent line if they are as concerned about pitch, watertightness, etc.

(post #115346, reply #1 of 24)

I would think it should just drain down into the drain line, and the vent should be sealed the whole way. You don't want escaping gasses leaking out into the walls/attic on their way to the roof.


Whether you AHJ or codes allow it may be a different story.


Here in Phoenix, I've seen dozens of commercial rooftop A/C units that drain down into the wall and out into the bathroom for that unit. There it's plumbed into the sink tailpiece.

(post #115346, reply #4 of 24)

We had run a small PVC pipe over to where the furnace was going to be for the condensate - separate from the sink vent. However, the HVAC guy was concerned about it because the pipe had very little pitch at all. It runs about 12 feet, elbows, and then runs another 12 feet or so - and does all that in an elevation of 12-14".

(post #115346, reply #9 of 24)

Keep in mind, I'm no HVAC expert or veteran plumber(which means someone else might well come along here and poke me in the eye for this), but that definitely sounds like too shallow a pitch for my liking. There may well be a heck of a lot of water in high humidity, and with the dust that'll accumulate, I'd much rather know I've got a good flow to keep it clear. A backup in the attic is bad news. 


If there's nothing nearer the outlet then that vent(12' away), I'd seriously consider popping it through the siding. That of course also depends on where it shows on the outside...:)


 

(post #115346, reply #2 of 24)

I'm reasonably sure it's technically a violation. Whether it's an actual hazard or not is a separate question.


There is no absurdity that human beings will not resort to in order to defend another absurdity. -- Cicero


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115346, reply #3 of 24)

by code here... it should drain into a wet trap  or  a traped "floor sink" with an air gap...


if it was my house and i was doing it...  shouldn't be a problem IF they put in even a small line trap  (that piece of pvc that has a little dip in it to make it a trap)


what you don't want to happen and it could... is for the air handler to suck air (in your case it'd be sewer gas) back into the unit via the  condensate drain... could stink up the place...  prob wouldn't ever happen... but a very clogged filter could cause it...


p

(post #115346, reply #5 of 24)

My unit is in the attic. The condensate line just stubs out of the siding about a foot, a few feet off of the ground. Yes, pitch is a concern. You want the water to move. You might be amazed at how much water those things put out with the air on full blast all day long.

(post #115346, reply #24 of 24)

Just  want to point out that since this is a drain for both a furnace and a/c unit, simply


running a drain to the outside can cause problems if the poster lives in a place where


temps can be expected to go below freezing.  I think he is from MA so that could be


an issue.


 


Assuming the furnace is a high efficiency unit it will create quite a bit of condensate in


the winter.   I've had a line running in an outside wall freeze on me before when


temps got to around 5 degrees.


 


Just something to condider!


 


Dan

(post #115346, reply #6 of 24)

Here are a few pictures of the setup. The gas and condensate lines are behind the unit, to the left. The second picture is zoomed in.

(post #115346, reply #7 of 24)

If you're in the attic with A/C you should also have a drain from the drip pan and/or a high limit cutoff float switch.    Standard condensate and pan drains in attics are notorious for clogging and backing up condensate to overflow.


Jeff

(post #115346, reply #8 of 24)

The guy who moved my furnace and A/C to the attic did exactly the same thing in my house in San Diego.  My vent goes straight down (it's the vent for my shower/tub).


I've wondered if that was the proper way to do it.  The guy I used worked for a commercial HVAC company at the time, and now has his own business.  There is a 3/4" PVC "P" trap in the drain line.   It's been that way for 5 years now with no problems, through some periods of heavy use. 


The installer just drilled a hole into the ABS vent and stuck the PVC pipe inside it.  I went to an HVAC supply house and explained the setup to them.  I wanted to see what they thought of it, and if they had a piece that I could use to make a more certain connection between the 2" (or 1 1/2") ABS vent and the 3/4" PVC drain pipe.  He said that it was a common way of connecting the drain, but they didn't have a fitting to secure it (he thought they might in the coming months).


One problem I did notice on a particularly humid day (which is rare here) was that more than a little condensation was forming on the outside of the 3/4" PVC drain pipe because the water in it was so cold.  I intend to cover it with foam pipe insulation to prevent this.

(post #115346, reply #10 of 24)

I think the thing to think about is this:  What happens when that line is filled with flammable gas.  Where is that flammable gas going to go... out into the atmosphere above your house, or is it going to build up in your HVAC system waiting for a spark?


Methane is flammable.


Rebuilding my home in Cypress, CA
Also a CRX fanatic!


I don't feel it's healthy to keep your faults bottled up inside me.

YAY!  I love WYSISYG editing!  And Spellcheck!

____________________________________________________

(post #115346, reply #11 of 24)

"Do it all the time" does not make it the correct thing to do.


SOP changes as the trades become more learned about potential hazards.


My attic unit was plumbed as you describe...but in 1973 that was SOP.


The replacement unit installed 8 years ago got "revised plumbing"!


My daughters new house attic unit was plumbed in 2004 and there is a condensate overflow pan piped to the exterior to exit over an exterior doorway.....if the unit malfunctions and leaks the pan catches the errant water and sends it dripping where they will notice as they go into the house. The propblem can be addressed immediately.


The actual condensate drain has it's own inline trap to prevent the fan from sucking air from the attic.  The condensate line empties with an airgap into an 1-1/2 trap which tees into the vent stack.  The air gap makes sure that the units air handler does not suck any sewer gas from the plumbing vent.


The safety aspect  is to prevent the air handler from moving methane from the plumbing stack into the living space.  As pointed out methane is potentailly explosive, but even more deadly as a toxic gas to humans.


This configuration allows for visual inspection of the movement of the condensate into a drain. Current hi-efficieny units produce condensate in both heat and cool modes.


Current SOP does not want the condensate drain piped in a concealed manner into a drain above a fixture trap and absolutely not directly into a vent stack.


...........Iron Helix

.......Iron Helix

(post #115346, reply #12 of 24)

Methane is not a toxic gas- the big risk is flammability.  It's an asphyxiant, meaning that if you breathe pure methane you're not getting any oxygen.  There's CO2 in the sewer gas too- also an asphyxiantl, except unlike methane it's denser than air and hence more of a worry in a low spot like a sewer.  There's probably H2S in the sewer, which is toxic- but not typicaly enough of it to be worrisome except for the smell.


The thing you really want to keep out of your house is the gawdawful stink...


To the OP:  there's no point in suffering over this thing.  Code aside, as long as the PVC hose is trapped (via a bend in the tubing) so backflow of stink out of the vent won't occur, AND  you make a solid leak-free connection between the tube and the pipe, you can connect this tiny flow into the vent line if it's handier than the drain line itself.  Get a 1/4" NPT tap, drill a 7/16" hole and tap the pipe wall.  Don't want to buy the tap?  Grind or file a couple flats across the threads of a steel pipe nipple- it'll thread plastic well enough for what you need to do.  Coat the threads of a 1/4" MNPT hose barb generously with epoxy, thread the sucker into the pipe wall, let it set and you'll have a lifetime connection.

(post #115346, reply #14 of 24)

I apologize for the improper terminology....dead is dead via asphixiation or toxicity!


If one choses to do a "non-code" installation then I would take argument with the  1/4" tap you describe for the HVAC condensate drain.


The normal exit on an HVAC is 3/4" and even that diameter will plug with "gunk" build-up.  1/4" diameter just isn't big enough to let the chunks flow past. 


The connector to the vent stack should not be inserted into the condensate line as the reduction in diameter will catch debris and clog. The condensate drain should run full bore all the way into the vent stack with no reduction of diameter.


IMHO............Iron Helix

.......Iron Helix

(post #115346, reply #17 of 24)

There's no way you're going to asphyxiate yourself with sewer gas unless you enter the sewer itself.


Yep, if it's a condensate gravity drain rather than a tube from a little condensate pump, 3/4 sounds about right, which throws my idea of drilling/tapping the pipe wall out the window.   In that case you'd need to cut in a fitting and install a proper trap, which is getting a little dodgy on a vent line.  The flow's still small relative to the diameter, so it should still work.


 

(post #115346, reply #18 of 24)

Double "Yep!"....................Iron Helix

.......Iron Helix

(post #115346, reply #19 of 24)

>>There's no way you're going to asphyxiate yourself with sewer gas unless you enter the sewer itself.

But sewer gas carries a number of nasties - that's why we try to stay away from it




"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

Howard Thurman

======================================== "Man's capacity for justice makes democracy possible, but man's inclination to injustice makes democracy necessary." Reinhold Niebuhr: 'The Children of Light and the Children of Darkness' http://rjw-progressive.blogspot.com/ ========================================

(post #115346, reply #16 of 24)

""My daughters new house attic unit was plumbed in 2004 and there is a condensate overflow pan piped to the exterior to exit over an exterior doorway.....if the unit malfunctions and leaks the pan catches the errant water and sends it dripping where they will notice as they go into the house. The propblem can be addressed immediately.""

That is the rule here and has been for a number of years.
Over the kitchen sink window is another acceptable location for termination of the overflow line.


They can't get your Goat if you don't tell them where it is hidden.

Life is Good

(post #115346, reply #13 of 24)

Don't know if it's code, but I'd think draining into a sink trap through a dishwasher-type tailpiece would work.


I drained my condensing boiler into the nearby clothes washer drain pipe and the inspector didn't bat an eye -- don't see how that would be much different.


Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #115346, reply #15 of 24)

>>The HVAC guy wants to tie into the vent for the kitchen sink as the drain line. He says they "do it all the time". Is this a concern?

Well, if the condensate drain isn't trapped, or if the trap fails, (such as dries up during non-air conditioning season) do you want sewer gas being able to get into the air circulated through your house?

Not to mention rules for wet vents.




"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

Howard Thurman

======================================== "Man's capacity for justice makes democracy possible, but man's inclination to injustice makes democracy necessary." Reinhold Niebuhr: 'The Children of Light and the Children of Darkness' http://rjw-progressive.blogspot.com/ ========================================

(post #115346, reply #20 of 24)

I'm a little confused, as the condensate line we had put in, also drains into the sewer - so I don't see the real difference. As George Costanza would say "It's all holes!"


Do people run condensate lines so that they just dump outside the house on the ground?

(post #115346, reply #21 of 24)

Some condensate do, some don't!


The overflow pan drain always does...............Iron Helix

.......Iron Helix

(post #115346, reply #22 of 24)

put a trap in first

As the twig bends- So grows the tree!!

(post #115346, reply #23 of 24)

What should you bait it with?


There is no absurdity that human beings will not resort to in order to defend another absurdity. -- Cicero


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville