Patio doors are the perfect way to let some of the outside in without having to actually open up. They are great additions to any house but when they leak air, either hot or cold, they cause a lot of energy loss and that can cost a lot of money besides making your home uncomfortable.
If you have a drafty patio door and the winter winds are making their way inside, you don’t have to barricade off the area. You can fix it. The first thing to do is figure out exactly where the draft is coming in. Wet your finger and move it close to where it seems the air is coming. You should be able to feel it. If you aren't sure, light a candle or a match and move it slowly around the area. When you are at a place where the cold winter air is coming in, the flame will flicker or dance.
The fix will depend on where the draft is coming in. If it is from the floor, you may be able to stop it with a simple draft dodger or draft stopper. You can buy one, make your own if you like to sew, or simply use a rolled up rug or towel (not the most elegant option) as long as it fits snugly against the bottom where the patio door meets the floor.
If you have a sliding door and the draft is entering from the non-sliding side you can simply use caulk to seal it. Use clear caulk and put it on neatly and remove the excess. After the caulk settles, use a match, a candle or a wet finger to make sure no air is moving through it. If the draft comes from the side where the patio door slides into the wall, you'll need weather stripping. Put the stripping on the wall side of the patio door and position it so that when the door is closed, there is no winter air coming through. Weather stripping is inexpensive, so if you don't get it right the first time around, try again.
Though not as common, latches and handles can leak as well. If yours are leaking, you may be able to tighten them with screws or place washers where they may be loose. If this isn't possible, use clear caulk to seal off the holes, even if they're very small.
The hardest leaks to fix are the ones coming from in between two sliding doors. You’ll need to use weather stripping, which can be tricky because it will need to be added between the doors. If you can’t get it into place, it’s best to stuff cloth between them and avoid using the doors as much as possible. Another fix is to cover the entire door with plastic on the inside. This may not look very good and it can be hard to position such a large piece of plastic, but if nothing else works, this option will stop the draft.