Thread: AC condensate drains and condensing furnaces (Whey? Yet again?)

OK…help me out here….

Condensing furnace with the condensate drain...

meeting an untrapped AC primary condensate drain at floor level...

and then draining into a floor drain.

The condensing furnace’s installation instructions say:

“The condensate drainage system is internal to
the furnace. It is not recommended to connect
additional traps to the exterior of the furnace.
Doing so will have adverse effects on the operation
of the furnace”

Pp 25 at http://www.nordyne.com/Literature/7086120.pdf

Back to first principles, as I understand it:

1) There should be both primary and secondary drains from the A-coil.

2) Both should be trapped at the level of their exit from the coil.

3) If they meet the furnace condensate drain below the level of it’s exit from the furnace, the AC condensate drain trap(s) do not constitute “additional” traps as defined in the furnace instructions.

Have I got it right so far?

If so:

What is a/the correct detail where they join the furnace condensate line?

Does anyone have a really clear picture or diagram of this, done right?

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Originally Posted by Michael Thomas

and then draining into a floor drain.

That's the confusing part.

Back to first principles, as I understand it:

1) There should be both primary and secondary drains from the A-coil.

2) Both should be trapped at the level of their exit from the coil.

3) If they meet the furnace condensate drain below the level of it’s exit from the furnace, the AC condensate drain trap(s) do not constitute “additional” traps as defined in the furnace instructions.

Have I got it right so far?

Yes.

The condensate drains (all of them which drain into the floor drain) should have an air gap above the floor drain. Each condensate drain line now has one trap, its own trap. The floor drain, below the air gap, does not count toward any other drain as a trap - they are totally separated by the air gap.

So (sorry I don't have a pic) an elbow and a short leg into the drain, ending well (several inches) above the trap seal but below floor level is a sufficient air gap, or not?

Originally Posted by Michael Thomas

So (sorry I don't have a pic) an elbow and a short leg into the drain,

Ending above the flood level rim the drain receptacle (the floor drain) creates an air gap, not down into the drain.

It also needs to end at least 1" above the drain cover and should end twice as high above the drain inlet (the drain cover) as the effective opening size. I.e., a 1/2" and smaller pipe (about 1/2 id) needs a 1" air gap, a 2" pipe (about 2" id) needs a 4" air gap. The height above the drain varies from two times to three times the opening size depending on if the air gap is close to a wall (three times) or not (two times).

From the IRC: AIR GAP,WATER-DISTRIBUTION SYSTEM. The unobstructed vertical distance through free atmosphere between the lowest opening from a water supply discharge to the flood-level rim of a plumbing fixture.

The above, though, are for potable water discharging into a non-potable water receptacle. See Table 2902.3.1 Minimum Air Gaps.

What you are referencing, though, is non-potable water discharging into a non-potable water receptacle. Like below.

INDIRECT WASTE PIPE.

A waste pipe that discharges into the drainage system through an air gap into a trap, fixture or receptor.

I'm not sure what the minimum air gap vertical distances are for those.

Well the point - apparently - is we really need an air gap... though in a condensate to DWV situation I can't get get very excited about it... as a practical matter a furnace/AC coil is gonna' have to suck awfully hard on that straw to do any harm.

What I still would like to see is a real clear diagram or picture of the dual trap condensate lines merging properly with the condensate discharge form a condensing furnace - I'm not sure I've ever seem it done 100% right....

Micheal, I don't have a diagram, but it seems clear to me that the easiest way to do this is just have traps at the exit of the coil, then a vent to allow the condensate to drain without draining the trap, then a separate drain line down to the floor drain, stopped a few inches short and secured over the drain to provide your air gap.
The same setup on the furnace drain except no trap as per the manufactures instructions.

Back to a few more first principles:

1) As I understand it, condensate drainage should be arranged such that single point failures cannot obstruct both a primary and secondary line - for example, a secondary line either has to run in dedicated piping to an approved discharge location or to a point where accumulated discharged will turn off the appliance (for example, to a pan with float switch).

2) But, I often see a primary AC condensate discharge join with a condensing furnace discharge before running to a floor or other drain - which would seem to be a situation in which a single point failure cam block multiple condensate drains. Is this allowed, as long as no additional trap is introduced below the exit of the furnace discharge from the furnace?

Hum... anyone ever see on of these?

http://www.eztrap.com/documents/broc...20brochure.pdf