Installing Fiberglass Pipe Insulation Adjacent to a Flue Pipe or Boiler Casing

Installing Fiberglass Pipe Insulation Adjacent to a Flue Pipe or Boiler Casing

Posted by BIP on 19th Nov 2018

Installing Fiberglass Pipe Insulation Adjacent to a Steam Boiler

Can fiberglass pipe insulation be installed in direct contact to a boiler? This is a common question/concern that we are asked on a daily basis. We fully understand the concern and we can assure you that it will be fine to insulate all the way up to the boiler casing. Please note that you want to keep the ASJ Max paper way from any open flame or touching a metal flue pipe. 

Importance of Insulating Boiler Headers:

The most important piece of pipe insulation is the one on the supply header coming right off the boiler.  Many homeowners choose to leave this pipe uninsulated because of fear of insulating too close to the boiler.  Because this pipe is the closest to the boiler its actually the hottest section of pipe and the biggest heat loss comes from this pipe being uninsulated.  

ASJ Paper Proximity to Boiler:

If you are concerned about the ASJ Max paper being too close to the boiler casing, we still recommend insulating the header pipe.  The only difference is you can cut approximately 1" of the paper off the end of the pipe insulation so only the fiberglass touches the boiler casing.

Temperature Rating of ASJ Max Paper:

The ASJ Max paper jacketing is rated for operating temperatures of up to 150°F so most likely there should be no concern with the paper touching the casing of the boiler which should be insulated and less than 150°F.  Please note that this is the temperature rating and not the burning temperature which is closer to 450°F.

ASJ Max Paper and Flue Exhaust Vent:

A bigger concern would be having fiberglass pipe insulation touching a flue pipe.   Depending on the type of boiler you have and the efficiency of the boiler, the flue pipe an get upwards of 400°F.  In the odd case where a supply or return pipe is in close proximity to the flue pipe, we recommend reducing the thickness of insulation near the flue so that the pipe insulation does not come in contact with the flue.  You do not want ASJ paper touching a hot flue pipe as this could be a fire concern.  

Owens Corning Fiberglass Pipe Insulation ASJ Max Paper Jacketing Proximity to Boiler Casing Flue Pipes