Things are getting steamy - boiler exhaust safety?
December 12, 2013 7:28 AM   Subscribe

New high efficiency boilers installed - great! But what exactly is in the condensate?

Our building is very old (late 1800s) and runs on steam radiator heat. Our landlord recently installed two new high efficiency boilers, and we know that the replacement was a big deal. However, we are wondering about the contents of the condensate coming from the boiler, and the proximity to windows and doors. Here is a picture of the vents (though both have downspouts fitted now).

We actually don't doubt that these vents from the boiler are in fact up to code, but outside of the legal allowances, is there any risk or unpleasantness to fear from the boiler exhaust? We are having a hard time getting a consistent answer. I think I understand enough to know that the condensate is mostly steam and not smoke per se, but we are still wondering about any potential things to look out for. If it matters, we live in a climate that is very cold in the winter (often -20 degrees Celsius or colder). Thanks for your help!
posted by analog to Home & Garden (5 answers total)
If what's coming out is steam, then there isn't any condensate. This is like a still, and distilled water is very pure.
posted by Chocolate Pickle at 7:33 AM on December 12, 2013

Best answer: If the boilers are burning correctly - and burning gas - it will be CO2 and water coming out. If they are not running well, it will be CO, CO2, and water.

If it is fuel oil, then, there is more to it (SO2 and some other stuff), but that doesn't look like a chimney for a fuel oil burner.
posted by Pogo_Fuzzybutt at 7:38 AM on December 12, 2013

Best answer: What is coming out of the vents depends on what the boilers are burning as fuel. If it's natural gas, which is likely in Canada, it's typically a mildly acidic water vapour (water and carbon dioxide). This is usually safe enough to be discharged directly (and legally) into ground water.

In short, for a modern NG boiler, I wouldn't worry about it. The biggest problem my parents' system has is ice build-up under the downspout in winter. You might want to put a drip catcher there to avoid a slip hazard.
posted by bonehead at 7:41 AM on December 12, 2013

It's not just water. The natural gas contains small amounts of sulphur, which creates sulphuric acid as part of the combustion process. This is normal and not a particular cause for concern; just don't sit around breathing in the exhaust gases.
posted by Dasein at 7:59 AM on December 12, 2013

Condensing boilers produce condensate that is slightly acidic (around 3.5 or so, which is between orange juice and tomato juice for acidity). As has been pointed out, the exact mix depends on what's being burned.
posted by DaveP at 3:53 PM on December 12, 2013

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