Could the vapor that comes out of the radiator be harmful to a person. The room got full of yellow brown spot all over the walls.

  • What type of chemicals do you use in your system? Some only water , some glycol, my area rarely freezes hard so the systems I work on are just water, the brown stuff is rust, even if glycol based it won't hurt you just don't lick it off the walls or let animals as it can cause them problems.
    – Ed Beal
    Feb 13, 2018 at 20:01
  • Only if your wife finds out! Seriously only some glycols are poisonous, propylene glycol is actually a foodstuff. Feb 13, 2018 at 21:01

1 Answer 1


Most likely not hazardous. The "yellow brown spots" are probably just from rust, and that's perfectly normal. When antifreeze is used in a hot water circulating system, it's pretty much always a non-toxic form, and it's actually unusual .vs. just using plain water.

In a system with iron components and no leaks, the oxygen in the water causes rust for a short time, and then stops rusting as the oxygen is used up. When the system leaks, more oxygen is available and more rust happens. But there is always rust in a heating system with iron components exposed to the water, and that's normal.

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