Why You're Losing Money - Air Seal Your Basement
Air Seal Your Basement
Second only to the attic, your basement is one of the leakiest parts of your home. The basement is rarely finished during the construction of your home and the builder usually treats it as unconditioned space. So the holes left over from the electrical, plumbing and HVAC contractors are still down there waiting for you.
Some of the leakiest parts of the basement are the sill plates and rim joists. As you can see in the photo above, the sill plate and rim joist sit on the foundation wall. The rim joist is the area with the silver foam board. Air leaks through the gaps and cracks all the way along your foundation wall where it can get sucked into your furnace or air conditioner and blown throughout your home.
Air Sealing Rim Joists and Sill Plates
The rim joist may already be insulated with fiberglass or it may not be insulated at all. Either way, air is leaking in because fiberglass does a better job at filtering air than stopping it. So pull it out and take a shop vac to the sill plate and rim joist. Use a snap blade knife with a long blade to cut pieces of rigid foam board insulation to fit into the rim joist area. Grab a can of Great Stuff with the long clear tube on it and seal off the perimeter of the foam board. Then run a bead along the foundation wall and sill plate. 
Heating ducts, plumbing and wires will inevitably get in your way. When they do, keep in mind that Great Stuff expands considerably and has about the same r-value per inch as foam board. Cut the foam board into pieces or a U shape to get around the obstacles and finish off the space with Great Stuff. Remember that plumbing pipes can freeze. Try to get as much Great Stuff or foam board behind them as you can. Never cover them from the inside.
Air Sealing Electrical Holes with Great Stuff
Air sealing electrical holes is really easy. Stick the tube down in the hole and squeeze the trigger until the foam comes out of the hole. Swirl the tip around the wire and you're done.
Air Sealing Large Holes
Contractors cut huge holes in your subfloor and attic to run the ductwork up through your walls. These holes are usally to big for Great Stuff alone which just drips all over your floors. A better option for these holes is to cut a piece of scrap plywood to fit around the duct and screw it in to the subfloor with 1" screws. Then squirt the Great Stuff around the remaining gaps.
Service Penetrations
In order to supply your home with electricity, cable, water, sewer and fuel, contractors cut holes in your foundation known as service penetrations.
If these holes aren't sealed they allow freezing cold air to pour in during the winter and hot, humid air in the summer. They're also a highway for mice, stink bugs and other pests.
A quick walk around your basement will reveal the condition of the holes. If you can feel cold air or see sunlight, pull out the Great Stuff or caulking gun and get to work. If you can't reach them because of the framing, try finding the penetration from outside and seal it off with silicone caulk.
Basement Windows
Some of the largest holes in the basement are your windows. Basement windows are usually single pane with little insulating value and rarely close right. Worse yet, they are probably close to your furnace. They allow hot or cold air to flow directly into your basement where it is sucked into your furnace and blown into your home. Driving up your energy bills and costing you money. If you only use your basement for storage, you may want to consider air sealing them with foam board and silicone caulk.