It is said to represent them, but they could be good or bad in theory or it could just be cold air.
cold air
Yes
It is never a good idea to restrict or block a cold air return.
yes
yes because they can withstand heat and cold but not smoke or fumes and this is how we know they are good indicators of air quality
Get the air out of your heater core.
Cold air increases air pressure
cold air is heavier than the warm air warm air has low water so it is hot and low heavy but cold air has a lot of water so it cold and heavy
Well, it can be when you need vitamin D. But remember if you are sick from worse than a cold you should get plenty of rest and follow your doctor's orders. Some drugs require you stay out of the sun because you can get seriously burnt. The sunshine is good for treating psoriasis (with a regimen prescribed by the doctor) and it is good for people who need fresh air and sunlight to lift their spirits.
well, blow dryers are a good type of way to dry your hair and it blows HOT air but if you use cold air its still okay. but to cold would make your hair freeze so i would probably say hot air
Cold air is compact air Hot air is less dense than cold air Ergo, hot air rises ; cold air sinks
the cold air pushes the warm air up and forms cumulus clouds