[dianedebuda]

One system, installed in 1976, connects to the septic system somewhere around the bath sinks. Have another system installed years later, that currently drains to the outside just below grade and is a pain to keep root-free. It would be awkward to change the outside drain situation, so want to investigate if it'd be possible to connect the 2nd system to the septic using a nearby new bathroom. Rural and no permits or inspections involved. This new 1/2 bath does not yet have drywall on the studs so it would be easy access right now if there's a correct way to do this. The older system was probably to code at that time, but shall we be generous and just say the plumber was inventive and did stuff that I wouldn't necessarily want to copy blindly.

I'm assuming this HVAC drain to septic situation is allowed by some jurisdictions, but just not finding a diagram to follow. I'd ask my long-time HVAC guy, but he retired and moved away.

 

[Herminator]

One question that might help others answer.

How many gallons of water will flow to this drain per day?

 

[dianedebuda]

Don't know what max is, but during hot, humid days see about an 6" diam puddle where drain exits. A pure guess would be a cup or so for each time the system turns off.

Know the design would have to prevent backflow of sewer gas. Have always had water in the p-trap outside the attic part of the unit even if it's been turned off for weeks. Have clear pvc there, so I can see it.

 

[Kennyd]

Our HVAC systems (two of them) drain into the sump pit. This met our local code in 2002/2003.

Is this an option for you Diane?

 

[RodW]

I checked the site used by home inspectors. A post there says " It needs an air gap/indirect connection where it can’t syphon back"

condensate drain to sewer line?? - Specific Inspection Topics / Inspecting HVAC Systems - InterNACHI®️ Forum

 

[dianedebuda]

Our HVAC systems (two of them) drain into the sump pit.

No sump pit - house on a slab.

I checked the site used by home inspectors. A post there says " It needs an air gap/indirect connection where it can’t syphon back"

I'd found similar statements too before posting here, but feels incomplete to me. Really would help to see a pic or diagram showing what's needed between the air handler & it's p-trap and the plumbing drain system including a vent stack. Assume there's height levels to be observed.

 

[Treefarmer]

No sump pit - house on a slab.

I'd found similar statements too before posting here, but feels incomplete to me. Really would help to see a pic or diagram showing what's needed between the air handler & it's p-trap and the plumbing drain system including a vent stack. Assume there's height levels to be observed.

Our air handler drain exits the cabinet in pvc pipe which has a T fitting with the long part of the fitting vertical. The top is open and the drain to the outside is connected to the bottom part of the T. Since the pipe exiting the cabinet doesn't run full, there is an air gap at that point. I hope this makes sense, I'm not home or would include a pix.

 

[Rule292]

I checked the site used by home inspectors. A post there says " It needs an air gap/indirect connection where it can’t syphon back"

condensate drain to sewer line?? - Specific Inspection Topics / Inspecting HVAC Systems - InterNACHI®️ Forum

I'm not the brightest light bulb... but I think the anti syphon is for things like water softeners or potable water sources that drain into the sewer. Or is the sewer water going to poison the heat pump?

I think the IAPMO is trying to compete with the NFPA for using stupid code mandates to create demand for unnecessary and expensive products for their code-making sponsors.

 

[MF231]

Can you shorten the existing drain so it comes out above grade?

 

[MadMadHoosier]

Our tankless water heaters use condensate neutralizers before draining into the septic system. Should work for HVAC systems also???

 

[rtgt]

I'm not the brightest light bulb... but I think the anti syphon is for things like water softeners or potable water sources that drain into the sewer. Or is the sewer water going to poison the heat pump?

There is usually a P trap of some sort at the HVAC unit where the condensate drain exits. The trap has to be deep enough to break the vacuum the fan can pull.

If the trap dries out the fan will pull air through the drain. Depending on the size of the fan, there can be enough static pressure to hold the condensate inside the unit while the fan is running. When the fan shuts off, then the condensate flows out and fills the trap unless the trap has a leak.

The air gap prevents pulling waste line fluids back to the unit if the HVAC trap is dry.

During the non-cooling season is when the HVAC P trap usually dries out. A little mineral oil in the condensate P trap will prevent the trap from drying out.

 

[Rule292]

There is usually a P trap of some sort at the HVAC unit where the condensate drain exits. The trap has to be deep enough to break the vacuum the fan can pull.

If the trap dries out the fan will pull air through the drain. Depending on the size of the fan, there can be enough static pressure to hold the condensate inside the unit while the fan is running. When the fan shuts off, then the condensate flows out and fills the trap unless the trap has a leak.

The air gap prevents pulling waste line fluids back to the unit if the HVAC trap is dry.

During the non-cooling season is when the HVAC P trap usually dries out. A little mineral oil in the condensate P trap will prevent the trap from drying out.

on the mineral oil suggestion.

My mini splits have condensate drain traps on them for this reason.

Was thinking about adding a condensate pump to the dehumidifiers in the basement instead of long hoses to the drain.

I was always told that condensate was like distilled water in that it contains none of the lime and heavy minerals of ground water.

 

[dianedebuda]

Our air handler drain exits the cabinet in pvc pipe which has a T fitting with the long part of the fitting vertical. The top is open and the drain to the outside is connected to the bottom part of the T. Since the pipe exiting the cabinet doesn't run full, there is an air gap at that point. I hope this makes sense, I'm not home or would include a pix.

I think I kinda visualize what you're describing, but not seeing the connection to the plumbing drain system and how sewer gas would be blocked. Doesn't sound like you have a p-trap like I do on the air handler.

My best guess is that the connection would have to be somewhere close to the sink basin, maybe even before its p-trap. Or maybe it should be a solid connection to the drain or even vent stack and the air handler's p-trap would block the gas. I just don't know. The air handlers are in the attics here, so almost zero chance of black water backing up that far.

I'm not the brightest light bulb... but I think the anti syphon is for things like water softeners or potable water sources that drain into the sewer. Or is the sewer water going to poison the heat pump?

I think the concern is for sewer gas escaping back into the house, not sewer water. At least it is for me.

Can you shorten the existing drain so it comes out above grade?

No, it comes out of the slab below grade. One of my not so bright decisions from years ago...

 

[rtgt]

 

[rtgt]

In the picture above, the connection to the septic drain is presumed to be above an existing trap. If it is not, you will need to add a P trap at the connection point.

 

[dianedebuda]

During the non-cooling season is when the HVAC P trap usually dries out. A little mineral oil in the condensate P trap will prevent the trap from drying out.

Mine is a heat pump, so there is no off-season.

I was always told that condensate was like distilled water in that it contains none of the lime and heavy minerals of ground water.

That's what I had heard too, so was a surprise to see that some jurisdictions prohibit condensate from being piped into their systems seeming because of its contaminantes. Not wanting the additional water load to process I could understand.

 

[rtgt]

Mine is a heat pump, so there is no off-season.

There is a no-cooling season. When the unit is cooling and there is humidity being removed you have condensate flowing through the drain.

When it is below 75 ( ) and you have the system in heating mode, there is no condensate being produced and the trap can dry out.

 

[Rule292]

Mine is a heat pump, so there is no off-season.

That's what I had heard too, so was a surprise to see that some jurisdictions prohibit condensate from being piped into their systems seeming because of its contaminantes. Not wanting the additional water load to process I could understand.

My mother would say "save that water for the steam iron"!

 

[dianedebuda]

In the picture above, the connection to the septic drain is presumed to be above an existing trap. If it is not, you will need to add a P trap at the connection point.

That's what I was thinking when I mentioned piping before the sink's p-trap. But putting it there I think could open another can of worms. So I can see it now: I'll have what looks like a medicine cabinet and when you open it, you see a Rectorseal EZ-trap like I use on the air handlers so you can verify that it has water in it to prevent gas back flow. FWIW: my condensate lines are only 3/4".

 

[rtgt]

I was always told that condensate was like distilled water in that it contains none of the lime and heavy minerals of ground water.

Condensate from a cooling coil is almost like distilled water, but there are other types of condensate that are not. Likely in the code book condensate gets lumped into one category.

The condensate from condensing boilers and tankless water heaters comes from the combustion process (flue gas) and is very corrosive.

Or maybe it should be a solid connection to the drain or even vent stack and the air handler's p-trap would block the gas. I just don't know. The air handlers are in the attics here, so almost zero chance of black water backing up that far.

Agreed. Gas can though & some gases you don't want to smell and others you can't smell and don't want to breath.

A trap at the HVAC unit, an air gap, and a trap between the septic line connection point and the septic tank is all you need. The air gap can be either at the HVAC unit after the HVAC trap or at the septic drain connection before the trap.