The place where your house meets the foundation is apparently one of the biggest sources of air leaks in a home, along with leaks in the attic. Sealing these areas can be a huge savings on your heating bill.
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Buy trash bags made from recycled plastic - if we create demand for recycled plastic, towns and businesses will step up recycling efforts.
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You can get this cool stuff at Home Depot that looks like bubble wrap covered on both sides with aluminum foil. It comes in rolls, and this summer we cut pieces to fit in several south-facing windows that were turning the house into an oven. You just press it into the window - no glue or anything. It almost totally blocks the heat coming in, and it's cheap!
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Much less expensive than air conditioning or fancy thermal shades. Of course it also blocks the light, but for a few strategic windows it was totally worth it.
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In the "you do what??!" category...don't flush the toilet so often! Seriously, try it. It sounds ridiculous, but it's totally not a big deal, and it's a great way to save water.