Thread: Can boiler pipes get hot enough to cause a fire if touching?

Hello all,

The house I inspected yesterday had a boiler. I have two questions about it:
Can the hot water pipes get hot enough to cause a problem if they are touching the paper vapor barrier on the insulation? The reason I ask is I noticed a black mark on the insulation paper right where a 90 (elbow) was touching the paper. It almost looked like a burn mark. Could this be from the flux or is it getting that hot?

The other question I have is why would the water heater be plumed into the boiler piping? It’s a natural gas wh and boiler.

Thank you for your help!
mk

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The insulation paper shouldn't be left exposed anyway. A warning to that effect is likely printed on the paper.

Originally Posted by Mike Krueger

Hello all,

The reason I ask is I noticed a black mark on the insulation paper right where a 90 (elbow) was touching the paper. It almost looked like a burn mark. Could this be from the flux or is it getting that hot? Thank you for your help!
mk

Is the burn mark a result of the torch when sweating the pipes? Pics would be helpful.

Originally Posted by Bruce Ramsey

Is the burn mark a result of the torch when sweating the pipes? Pics would be helpful.

No it's just the spot where the pipe is touching. I would sure think they would have removed the insulation before working on the pipe.

Not sure how to make the pic small enough to work on this site.
mk

Not possible. Water temperature could never get hot enough to cause burning. Paper would likely need to approach 400 degrees to burn.
You were not too clear on piping but could be that the boiler has a domestic hot water coil within to supply domestic hot water.

Actually, paper can ignite at temperatures under 250 degrees. The longer a combustible is exposed to heat the lower its ignition point becomes. It's why charred word will ignite at lower temperatures than wood that has not been charred. Paper will begin to yellow at 150 degrees and ignite as low as 218 degrees.

It's like fireplaces. People use an unsafe fireplace for years with "no problem." Then one day comes along when there is one.

pyrolysis

I believe what you might be seeing is the leaking through of the material on the back of the insulation paper. It sometimes looks like mold as well. Correct me if I'm wrong please.