Not sure where the air is leaking in? On a windy day, light a candle or incense stick and then pass it closely in front of the likeliest areas — around window and door frames, along the baseboards, and around electrical outlets and light switches. Take note of any areas where the flame or smoke flickers.
Caulk around window and doorframes (being careful to avoid any moving parts) and along the top and bottom of baseboards. Buy a colour that matches the shade of your trim, or opt for clear to blend in.
For any gaps larger than about ¼” wide, you’ll want to seal those with spray foam. One place to look is on the outside wherever your waterline, hydro, and other services penetrate the exterior wall.
Another easy DIY project is to buy weatherstripping kits which include a door sweep and peel-and-stick foam for exterior doors. You can also lay a “door snake” along the inside of the door to block the gap. You can buy these or make one yourself from an old shirt sleeve or pant leg.
If your windows are just single panes of glass, you can temporarily seal them for the colder months with plastic film kits that you stick in place.
Drafts can also creep in through your light switches and electrical outlets. Remove the faceplates and install fitted foam gaskets in behind.
Finally, on really windy days, close the curtains for an added layer of protection.