GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Fill chimney with insulation?

[email protected] | Posted in General Questions on
I will seal it at the top and bottom, but that leaves 2 storeys of exterior wall of brick then cavity then brick then inside – no insulation. 
My chimney does not have an insert / metal flue, just brick.
I calculate it will take 0.3 bags of fiberglass @ $78/bag or 1.16 bags of cellulose @ $16/bag to fill the chimney.  I may be guilty of overthinking, but I made a spreadsheet (which you can comment on or copy):
I would need to get the insulation chopper/blower onto the roof (easy enough from my balcony to the addition roof and from there to the lower-slope part of my barn-style roof), and do the work on a day with no wind.
Would there be mold risk?
(The chimney is 100 years old, but the mortar is in excellent condition, even though I know it has had no work in at least 33 years.)

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    DCcontrarian | | #1

    What's more important is to make sure it's air sealed and vapor sealed. Brick has a very low r-value -- 0.2 per inch -- so filling the core with insulation doesn't appreciably change the insulation value of the whole assembly, the brick provides a heat path around the insulation.

    1. [email protected] | | #2

      I'm imagining I could dangle a hose from the top of the chimney and spray silicone or something in all directions as I gradually pull up the hose. Any idea if that product/service exists? Would that help? The brick would still provide a heat path around the insulation. I love the look of my 100-year-old bricks - gorgeous colors, I say, but the chimney is at a rarely-seen part of the house. Should I spray the exterior of the chimney with something?

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |