One of my long-term insulation projects is the basement and heater. Right now the temp outside is 30 degrees, it’s 68 degrees in the house, and it’s in the low 50s in the basement. I’ve started replacing the old single-pane basement windows but none of the hot or cold ducts on the heater are insulated so I’m assuming I’m wasting a lot of energy.
I’m looking for tips on insulating the hot air plenum, which is pretty big: about 10 feet long, 1 foot deep, and 2 feet wide. The ducts all join this plenum and their runs are pretty short before they go into the walls.
So far my choices seem to be: 1) glue/caulk styrofoam boards to the plenum, and tape the outside of the seams, 2) wrap fiberglass around the plenum, or 3) wrap honeycomb foil around, taped with foil tape. Looking for any input as to which might be best.
I would also like to insulate the cold air returns, since they’re 30 feet long. The difference is that the cold runs between the joists; there’s just a piece of sheet metal spanning two joists across the entire basement. Can I seal the sheet metal to wood joint with caulk? Should I insulate them the same way as the hot side?
Thanks.
Bill
Replies
Hi,
This may not be the best way to do, but I used the fiberglass product that is about an inch thick, and is somewhat rigid -- if you cut a piece off the roll, it is stiff enough to stand up straight. I wrapped these pieces around the rectangular duct with some overlap. I just used 16d nails to pin the overlapped ends together (like using a sewing pin to hold two pieces of fabric together). Seems to work fine -- has been in place for 5 years.
Be sure to seal all the duct joints first with duct mastic.
Insulating the basement ducts will make the basement run cooler, since you won't have as much heat loss from the ducts to the basement.
If you want the basement to run at a comfortable temp, then you probably need the double pane windows and wall insulation?
Gary
The rigid foam will give you the most R-value, fiberglass next and the bubble foil very little (R 1 to 2). You can seal around odd shapes with expanding foam.
Sealing the duct joints is at least as important. Mastic will work, or butyl-foil tape. Seal the return duct but don't bother insulating it.
But be aware that, by doing this, you might lower the air temperature in the basement enough to risk freezing pipes on a very cold night.
Solar & Super-Insulated Healthy Homes
I have used most of the product types shown on this web site:
http://www.achrnews.com/Articles/Technical/b287e83ad6c5a010VgnVCM100000f932a8c0____
Along with sealing the ducts they are fairly cost effcient if you do it yourself. Labor for a pro to do the insulation pushes the return on investment out pretty far for most people in my mild climate.
Along with your new windows, you may want to look atsealin the rest of the basement. If the joist bays are exposed you can do wonders witha few cans of spray foam, caulk and some 1" rigid foam board.
Many older home have basements that are literaly the bottom of a chimney stack. As the HVAC system runs and the heat rises through the rest of the house and escapes out of all the unsealed openings on the upper floors, it draws cold air into the basements. Stopping the upper floor leaks will help alot, but stopping the infiltration of cold air in the basements is often easier when the spaces there are unfinished. Do both and your results will be immediate and often dramatic.
Generally, seal the ducts first w/ seal mastic or pressure sensitive foil tape ... just NO grey duct tape. Insulation will not take care of leakage ... and leakage on the return side can suck e.g. fiberglass into the duct.
I take it you aren't conditioning your basement?
I would avoid polystyrene insulation ... use rigid or batt fiberglass insulation. Polystyrene or any foam insulation unprotected is a fire hazard and code violation, I believe. While good theoretically, it's not good to do that. Your BO would probably cringe at the idea.
Thanks for all the tips. It sounds like the best thing for me to do is seal the ducts and then insulate the basement, not the ducts.
Bill
Get a tub of duct work mastic, to seal the seams of everything. Very easy to do and its quick. Get a cheap pair of cotton work gloves and just smear it on every seam or anything you think might be leaking. Just put it on thick. Insulation is cheap, insulate the basement too. use fiberglass or rigid and get cans of spray foam and seal all pipes, wires or anything else.I would also insulate the duct work too. It might be a pain in the butt to do but if its possible, I would. You want the heated/cooled air to go where you are asking it to go, not lose heat/cool on its way through the ducts.This site has some materials for ideas. You can buy from them or just get some product ideas and shop locally. http://www.energyfederation.org/consumer/default.php/cPath/30_743Also, check state and federal tax and rebate programs, you might get rebates for the upgrades or be able to write it off on your taxes.