Air sealing is one of the most cost effective ways to save energy. Often it takes just a couple tubes of caulk and some time to make a significant improvement. It may come as a surprise, but some houses lose half of their heat to air leakage – the same amount that is lost through all the walls, ceilings, windows, doors and foundation. If not half, very often 30% or more!
Sometimes air sealing is a little more involved. Sometimes, air barriers need to be built; sometimes, air sealing should be combined with insulation (foam comes to mind first); sometimes, special procedures are needed to make air sealing effective and safe. The latter is the case when sealing the gaping cracks around a wood stove chimney. Here is how to do it well…
First, be sure the chimney is properly flashed; you don’t want to seal what would amount to a sponge, if water was leaking in!
Confirm the chimney pipe (brick chimneys can be air sealed too, but that is another story) is insulated and code rated to be within 2” of combustibles. This is critical for safety sake.
Here is the first trick – purchase a 3’ length of “High Temperature Insulation,” such as Knauf Insulation’s “1000° Pipe Insulation with ECOSE Technology.” This insulation is made with glass fibers that do not burn and can be in contact with the insulated stove pipe. The insulation is 2” thick, so it should bridge most the gap between your stove pipe and combustible framing. You don’t need 3’ but that is the typical length these products are sold in. If you had two chimneys to air seal, you could cut in half. Knauf Insulation’s product comes with or without an outer shell. The shell has a self-sealing tab for easy installation. Place it around (inside diameter should be about equal to the outside diameter of the stove pipe) the stove pipe, seal with the tab, and push it between the framing toward the roof.
Foam the gap between the high temperature insulation and the framing – regular foam is fine.
Next trick – cut twenty 2” strips of metal (not fiberglass!!!) screen about 10” long. Bend each strip at 4” in a right angle to the right, 2” later bend right angle but to the left – see diagram to left.
Attach the screen to the high temperature insulation and stove pipe – see diagram to right – using metal wire. I use masking tape to hold a bunch of strips in place and then wrap with a metal wire and remove the making tape. Also it is easier to apply just half of the strips at a time and then wrap with another piece of metal wire.
Finally, a little like icing an upside-down cake, cover the screen with furnace cement. Be sure to fully penetrate the screen to seal to the insulation above and the stove pipe below. Let dry and then check to see if there are any holes remaining and if so, fill them. You are done – a very air tight connection that is very safe! See finished project at top.
NOTE: Do not use ordinary fiberglass insulation - use high temperature insulation. Do not use fiberglass screen - use metal screen. Do not use string or tape to attach the metal screen - use metal wire. Be careful, be safe!
I have checked this sealing detail with Town of Ballston Building Inspector. You should check with your town before installing.
Dan Gibson is the Reporter and Chief Coordinator of Our Energy Independence Community (http://www.OEIC.us). Previously he performed home energy audits for five years in NYSERDA’s Home Performance program and new home ratings in the New York ENERGY STAR Home program. He is currently building a 100% Solar Home. He can be reached at DanG@OEIC.us.