Connecting pumped A/C condensate to a storm water riser 1

[Benj107]

What engineering rationale would prohibit disposing of pumped air-conditioning (A/C) condensate to a storm water riser without an air gap?

The National Standard Plumbing Code (NSPC) requires routing A/C condensate through an air gap before it connects to a pipe in a plumbing system.

I think the NSPC errs in making no distinction between the four possibilities where condensate from fan coil units:
[ul]
[li]Flows by gravity.[/li]
[li]Is pumped.[/li]
[li]Is routed to a sanitary waste pipe.[/li]
[li]Is routed to a storm water pipe.[/li]
[/ul]

Though many jurisdictions prohibit disposing A/C condensate to a sanitary waste pipe, it seems reasonable to require an air gap when connecting to a sanitary waste pipe.

I don’t think it seems reasonable to require an air gap for pumped A/C condensate connected to a storm water riser.

If check valves and shut-off/isolation valves are used at appropriate locations, I see nothing wrong with making a direct connection of a condensate disposal pipe to a storm water riser.

I know “the code says so,” but I want to seek a variance.

What reasonable engineering rational could there be for requiring a air gap before connecting pumped A/C condensate to a storm water riser?

 

[Compositepro]

The condensate drain from an A/C unit needs a trap to prevent air flow through the drain pipe. For the trap to work properly there needs to be a vent or air gap downstream from the trap.

 

[willard3]

Traps are designed to prevent explosive gasses entering habitations. Sewer pipes carry explosive gasses, storm drains don't if they're completely separate from the sewer.

 

[Benj107]

Compositepro, there is a trap before the sump and an air gap in the sump of the pump, comparable to:

This image is not the actual installation I am asking about, which collects condensate from a number of FCUs. This image was found on the internet for the purpose of illustrating the possibility of using a trap and an air gap upstream of the pump. No check valves or isolation valves downstream from the pump are visible in the image.

I don't see why another air gap should be required before connecting the discharge from the condensate pump to a storm water riser.

 

[PEDARRIN2]

Old school thought would allow condensate to go to storm (outside).

Code doesn't allow it (at least where I design), but inspectors will "allow" it. But requiring an air gap on an interior storm pipe is not a good idea, since occasionally storm pipes will surcharge during an intense rain event. Having the system open to the atmosphere on the inside of a building is just asking for a fountain of water to happen.

Instead of a storm pipe, can you take it to a mop basin or a nearby floor drain?

 

[Benj107]

One thought was to use floating ball-check type of backwater valves between the air gaps and the storm water risers,
comparable to this:

https://www.zurn.com/media-library/web_documents/pdfs/specsheets/58903-pdf

But good locations for the backwater valves have not been found.

We talked about disposal through mop sinks, but the client is wary of a sink overflowing if its drain clogs or if their staff has reason to intentionally plug a drain for a prolonged time.

We hadn't considered floor drains. They could be difficult to reach without creating trip hazards.

Both the mop sink and floor drain go to the sanitary sewer. The state's environmental rules favor disposal of A/C condensate through the storm water system unless it is impractical to do so.

The main impracticability being encountered is the requirement to install an air gap before connecting to the storm water riser, which seems to be an over-the-top requirement (or a rule that was made easier to write by ignoring distinctions between pumped/gravity flow to sanitary/storm sewers) with no engineering rationale that is apparent to me.

 

[PEDARRIN2]

If you have to take it to storm and have to use an airgap, then install the backwater valve between the air gapped discharge and the storm pipe (sorry for the crudeness of the drawing)

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Storm Pipe

Adding backwater valves on storm is done when there are lower level drains which could flood when flow from higher levels surcharges. Not done often - but it is done.

 

[dbill74]

The pump and its reservoir is your condensate drain air gap.

The pumped condensate is under pressure. Going through an air gap is going to make an awful mess as the condensate pump tries to push water through the air gap. You also have the potential to overwhelm the receptor portion of the air gap device causing an overflow (and mess).

If the storm drain does start surcharging as Pedarrin suggests, the storm water will back through to the condensate pump. Which will then try to push it back to the storm line when its float reaches the full point. Having a check valve or other backflow device on the pumped condensate will be sufficient to prevent backflow into the pump's reservoir. Also connect the pumped condensate to the highest point in the storm system as possible.

Condensate pumps do not come in a one-size-fits all size; get one with extra head capacity to overcome any storm water surcharging.

Note: Without a condensate pump to collect A/C condensate first, I would not even consider connecting A/C condensate to the storm drainage system, not even with an air gap. The risk of surcharging and the resulting mess is simply too great. If a local ordinance prohibited me from going to a floor drain connected to the sanitary sewer, my first choice would be to take it outside via gravity.

 

[Benj107]

I like it -- the code doesn't say where the air gap should be.

Thank you.

 

[PEDARRIN2]

From a plumbing code perspective, a condensate pump is not an air gap - it is still a physical connection. A check valve in the system is still not the same backflow prevention of an air gap. The backwater (check) valve is intended to prevent the mess when surcharging not protect the two systems.

Also, anything downstream of said air gap is part of the storm system. The smallest storm pipe (in my area is typically 3"), so anything downstream of this has to be 3". Also, a proper air gap fitting (like for the reduced pressure backflow preventers) would largely mitigate any mess from a condensate pump. I doubt a condensate pump can flow what a 3" vertical pipe can flow.

I am not saying it would not work - but you run the risk of the plumbing inspector rejecting it. Take it to a sanitary drain or put the air gap and backwater valve in.