Search the forums

Loading

Condensate Line to Sewer Pipe

PrezMFL's picture

Hi everyone, I was searching the internet for some advice and found this site and was hoping you guys could help me out.  A little background...I bought a house last June and this past winter I woke up one day and saw a wall with water damage.  Turns out my condensate line from the furnace/AC unit that terminates outside froze causing backup into the house.  Had a plumber come out and give me an estimate to relocated the pipe inside so it won't freeze.  He suggested connecting it to the sewer pipe and using a trap to prevent sewer gas from backing up.  Sounds scary to me!  Talk to a home inspector friend of mine who said he wasn't crazy about the idea, what if the water in the trap freezes (it's in my attic) then I would have a backup.  

I just want the problem taken care of and am tired of worrying about it.  Since it is in my attic, I don't have much choice where to relocate the drain.  Any help or comments would be appreciated, thanks!

Since it is in my attic, I (post #189841, reply #1 of 26)

Since it is in my attic, I don't have much choice where to relocate the drain.

I don't understand this.  If it's in the attic you have a plethora of options.  Don't you have a laundry room?  Run the line down through the ceiling and into the washing machine standpipe.  Or you can make a connection near a sink, running the hose down through the wall.


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

I like the idea (post #189841, reply #2 of 26)

of dropping it into the washing machine standpipe or better yet into a laundry tub, if there is one.

But if it is cold enough to (post #189841, reply #3 of 26)

But if it is cold enough to freeze in the attic, I'm thinking either the trap in the furnace is going to freeze or the condensate will freeze before it gets out of the attic.

So you route the hose under (post #189841, reply #4 of 26)

So you route the hose under the insulation.  If the furnace runs often enough the trap won't freeze, but to be sure the trap can be wrapped in heater tape or the furnace can be enclosed in a box to put it inside the "envelope".


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

Some clarification... (post #189841, reply #5 of 26)

The condensate never froze in the attic, it was freezing at the point where it left the house, outside.  That was the plumbers reasoning why it would be safe in the attic.  It never froze in the attic, it was freezing outside so the trap would be safe.  

The only part that (post #189841, reply #6 of 26)

The only part that would/should freeze would be the trap of the condensate drain as you should not be using the A/C in the winter, right? If the trap is covered by insulation you should be good to go.

BTW - condensate line to sewer is common ... but yes, must have a trap.

There ain't NO free lunch. Not no how, not no where!

The furnace condensate will (post #189841, reply #7 of 26)

The furnace condensate will be hot enough to begin with that it will flow down to the washing machine drain (or, into a dishwaher tailpiece in one of the sinks). Make sure there are no bellies in the line to trap water.

A trap in one of the attic plumbing vents would freeze as it sits there between furnace firings.

If you can't get to a drain below the attic, a p-trap in the attic would work if it is located so that the dip of the trap is touching the ceiling and you have plenty of insulation above and around it. What you're aiming for is to allow heat from the ceiling below to reach the p-trap, but to have the insulation isolating the trap from the cold attic.

But not when the furnace is (post #189841, reply #8 of 26)

But not when the furnace is not running.  And there is usually some left in the collector box/tubing leading to the furnace trap.

I just get leery about situations like this when I can't actually see the setup.

I'm assuming that this is a condensing furnace.

I also assume it's a (post #189841, reply #9 of 26)

I also assume it's a condensing furnace, and you're right about the collector box, but I've never seen one freeze here with winter temps down to -25 F.

I think that must be due to the ducted warm air that will always fill the furnace cabinet, and that the collector box is tight to the cabinet.

Good perspective since I was (post #189841, reply #10 of 26)

Good perspective since I was thinking A/C condensate line, not furnace. Sounds like some clarification in order from the OP?

There ain't NO free lunch. Not no how, not no where!

Uh, if it was just A/C how (post #189841, reply #11 of 26)

Uh, if it was just A/C how would he have had the line freeze up and cause an overflow?


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

eh ... you're right!! Duh. (post #189841, reply #12 of 26)

eh ... you're right!! Duh. Little slow on the uptake the other day. I've got cooling on my mind ... it's been over 100 the last few days.

In my condensing furnace, I've a plastic flue w/ a 'T' on it and a flexible tube looped and draining to the ground in an open spot in my mech room. The loop has water in it, but I've never seen it drain any water out of it.

What a strange situation. I guess he needs to run his insulation around the trap to protect it. I'd think the flue gas would keep it relatively warm. If the trap freezes and backs up, it would seem you got water in your heat exchanger (maybe I'm STILL missing something ... it's 5am). :)

There ain't NO free lunch. Not no how, not no where!

There's supposed to be a vent (post #189841, reply #13 of 26)

There's supposed to be a vent at the top of the drain run for a condensing unit.  Water should eventually run out of that (though it may back up into the HE some prior to that, I suppose).


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

Not sure what you are (post #189841, reply #14 of 26)

Not sure what you are describing Dan. My vent/flue comes out of my unit, goes horizontal where I put a T in pointing down w/ my flexible loop of tubing is attached. The loop acts like a P trap allowing the conensate to drain out of the flue into the tubing and then e.g. to a drain or whatever. The loop/trap simply keeps comustion gases from going into my mech room and the tubing allows the unit to drain the condensate.

There ain't NO free lunch. Not no how, not no where!

I'm not talking about the (post #189841, reply #15 of 26)

I'm not talking about the vent, I'm talking about the drain, which comes out of the unit.  Generally it feeds out the side into the leg of a tee, with one arm pointing up, left open to vent, and the other arm pointing down into the drain pipe.

I can't see why you'd need a separate drain pipe out of the flue, since it should drain back into the unit.  And the trap in the unit is much more reliable/safer than the trap  you're using.


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

Mine wasn't designed to drain (post #189841, reply #16 of 26)

Mine wasn't designed to drain back into the unit. I don't think I've ever seen a condensing combustion appliance allow the condensate to drain back to the unit ... always had a drain point somewhere in the flue vent. My install instructions specifically had me do it the way I described. I'm no expert, though and only have some limited knowledge. I've seen a few boilers just recently and they had the condensate drain in the bottom of the flue after it 'T'd out of the boiler

There ain't NO free lunch. Not no how, not no where!

I've never seen a condensing (post #189841, reply #17 of 26)

I've never seen a condensing furnace that DIDN'T drain back to the unit.  The instructions tell you to slope the flue back to the unit.

(Maybe they do boilers different from GFA units -- very few boilers around here.)


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

Mine's a water heater (used (post #189841, reply #19 of 26)

Mine's a water heater (used for space heat) and the other's I've seen are boilers, so maybe the FA furnace is the difference.

There ain't NO free lunch. Not no how, not no where!

There are relatively few true (post #189841, reply #20 of 26)

There are relatively few true condensing domestic water heaters.  Yours probably just cuts it close, so that most condensation happens in the flue.

A true condensing furnace has a flue temp below 212F and a significant amount of condensation (probably most) occurs in the unit itself.


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

I assume my flue temp is (post #189841, reply #21 of 26)

I assume my flue temp is below that ... it's ABS plastic.

There ain't NO free lunch. Not no how, not no where!

I doubt you have a condensing (post #189841, reply #22 of 26)

I doubt you have a condensing water heater.  Where is the fan? on top of the unit?  Then you have a very ineffecient water heater.

Could be wrong though.  (hedging my bet here)

Yes, the fan is on top of the (post #189841, reply #23 of 26)

Yes, the fan is on top of the unit (induced draft I believe this is referred to). Honestly I don't know if it is a "condensing water heater" or not. I did find out after I purchased it that it wasn't a high efficiency unit (e.g. 90% plus), but it still uses plastic flue pipe and I had to install a drain for the flue gas condensate. This is/was a bit confusing to me. I thought anything w/ low temp flue gas was a high efficiency appliance. I was a bit surprised when I went to get a rebate and found out the unit didn't qualify.

There ain't NO free lunch. Not no how, not no where!

You're right about no free (post #189841, reply #24 of 26)

You're right about no free lunch.

  All those heaters do is take room air and add it to the exhaust so the temp is low enough that plastic pipe can be used.   

Forced draft.   Positive pressure in the exhaust pipe.    (induced is usually negative pressure)

So instead of just the usual products of combustion being exhausted outside, now you exhaust a huge amount of tempered inside air that has to be replaced with outside air and tempered again. 

Soooooo.............. now you have the cost of running the water heater + the cost of running the fan + the cost of tempering the exhaust air + the extra cost of the water heater

BTW, make sure the air is dust and lint free or you will eventually have the cost of a service call for the fan.

Now that you mention it, (post #189841, reply #25 of 26)

Now that you mention it, you're right about the room air added to the combusted air. Someone mentioned that to me (now that my memory is coming back!). I thought ... well ain't that just stoopid. Silly me for buying it w/out getting the details.

My definitions of forced vs induced draft are a bit different than yours. Forced draft is positive pressure in the unit ... fan on the combustion intake and induced draft is negative pressure in the unit (still positive on the downstream side of the flue) ... fan on the exhaust end of the unit.

There ain't NO free lunch. Not no how, not no where!

In some non-condensing (post #189841, reply #26 of 26)

In some non-condensing furnaces the cooler temp (for pastic flue) is achieved by simply mixing air in with the flue gas, post-combustion.  This of course plays hob with efficiency if the mix air is drawn from inside.


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

And, in any event, there's (post #189841, reply #18 of 26)

And, in any event, there's still got to be a drain out of the unit, if it's really a condensing unit.


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