Even if you have new windows and doors, they can still be drafty and cold. It’s possible that whoever installed them didn’t seal up gaps around the rough openings. But you can fix this fairly easily with a can of spray foam. You just need to remove and replace the trim.
Air leaks from the heated part of your home to an unheated attic cause heat loss. They also cause air movement or, drafts. Seal up these air leaks with insulation.
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The weather stripping around your entry door may still be intact, but is it doing its job? Old weather stripping loses its flexibility with age. If yours is old and brittle, replace it.
This one’s less obvious, but it can be a major source of cold air intrusion. Dryer vent covers are supposed to flap closed when the dryer isn’t running, keeping cold air out. But if the cover is coated with lint or otherwise faulty, the flap might stay propped open, creating a 4 in. diameter pathway for icy winter air to enter your home.