Thread: Water Heater and/or AC Condensate pans

Why would the code require an airgap from the discharge pipes of WH and AC overflow pans when they do not connect to any potable water source? Instead of just requiring an airbreak between the discharge pipe and floor drain. (I am not referring to the T and P discharge line, just the drain pans?)

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Think about it this way. You have a water heater sitting in a pan. The water heater has a slow leak, you have a rat problem, you put out poison, the rat crawls in the pan where the water is and dies. Down the street there is a structure fire, the fire truck hooks onto a fire hydrant and turns the pumps on, the pumps are of greater pressure that the operating pressure of the house that has a dead rat in the pan. Water pressure drops at the house and the dead rat's innards are sucked into the water heater and then on into the potable water because there isn't an air gap...a dirt dobber build a nest in the end of the drain line and this doesn't let the water drain out.

Does that answer your question?

Half way. Thanks, but then about the AC system. It is not connected to the potable water system. It is making it's own separate water through condensate. Thoughts?

And one more question regarding the water heater. Is there not a backflow preventer somewhere in this mix? I know my pool has a big ol' rpz valve on it to prevent reverse contamination, I assume.

As for the AC system, I would want to keep that discharge pipe clean and dry as to avoid bacteria growth which could cause a stench to enter the plenum, and then from there into the home. I would say a back flow preventer is not 100% in eliminating a cross connection with the pan, so Wayne's comment comes back to haunt. Would you really want to provide a slight obstruction in a discharge pipe to an over pressurized HW tank that is trying to "relieve" itself?

An air gap is the very best type of backflow prevention available.

Isn't a backflow/air gap device in an AC system an attempt to prevent the spread of contaminants like those that cause Legionnaire's Disease?

The post was about drain pan drain lines, not the relief valve or condensate drain from the air handler. How would you back flow into potable water from the drain pan line? The pan wouldn't be above the bottom of the water heater.

To answer the question, it is probably required just to make sure that any sewage overflow from backed up pipes is in an area that it may be expected, rather than at the water heater or air handler pan. There may be some situations where the drain pan would be the lowest point in the house drainage system.

The pans are also allowed to drain to the outside of the house, or at least they are in my area. That would be my preferred termination for the drain pans.

Originally Posted by Elizabeth Franke

Half way. Thanks, but then about the AC system. It is not connected to the potable water system. It is making it's own separate water through condensate. Thoughts?

I don't think there is a requirement for the pan to have an airgap that would sit under an HVAC unit. There is a requirement for one if the discharge line from the evap coil discharges into a wet vent, floor drain or a sink trap. The reason for it is so that nasty little biological critters are not sucked into the airstream. Remember that the evap will actually suck air back into it from the drain port, and this is the reason that that drain line needs to have a running trap on it.

For some reason I think we all might be talking about different things?????!!!!