Question for the group: Do you write up heat pump condensate drains into cast iron roof drains? How?
Condensate drains have been going into cast-iron drains for decades. I would never write this up it’s not an issue.
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The article you posted seems to be talking about condensate from gas fired appliances, not heat pumps. Air conditioning condensate is close to pure water, condensate from gas furnaces and water heaters has combustion products mixed in that make it acidic. People regularly put more corrosive liquids down sinks and into metallic drain systems than their air conditioners do.
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You would have to write up rain & snow water going into that drain, too 
The copper drain line would also also break down if the condensate was corrosive. It would have to be plastic. The drain pan is probably metal, too. You get the picture.
Michael is correct, don’t confuse condensate from exhaust gasses with that of an AC evaporator coil. In a heat pump, you will have both coils acting as the evaporator coil depending on the heat/cooling mode.
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I don’t see an upward discharge. Looks like a “T”.
Not necessary.
You’re right, I’ve muddled two topics here.
HVAC condensate should be clean.
High Efficiency Gas Furnace condensate should be corrosive.
Here’s a neutralizer for gas furnaces, with refillable active ingredient:
That may be just the effect of “constantly wet” rather than corrosion, eh?
Corrosion is a broad term. It occurs under many circumstances. Water is just one chemical which can accelerate the process. Acidic corrosion is another. Many metals are designed to resist different types of corrosion. Potentially even the drain pipe you are concerned about.
Nobody’s using Cor10 steel for drainage pipes or grilles, as far as I know. That would do it.
I my area cast iron lasts about 100 years underground, and much more than that above ground. But it won’t last as long if constantly wet, compared to drying out between uses. I’m concerned for the impossible to replace older cast iron floor drains, that are now getting high efficiency furnace condensate from water heaters, essentially every day.
I understand what you are saying. You are concerned the condensate may accelerate deterioration. And it probably will.
So, my next question is “what rate will it accelerate the deterioration?” And, is this accelerated rate “report worthy”?
The neutralizer you posted (if it works) might be a worthy recommendation as preventative maintenance and is likely cost effective.
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