If it's still cold in your neck of the woods, you've turned on your heater again, and you're noticing what seems like a rise in humidity, it's time to do some investigating. The rise could be due to something minor, but it could also be a sign your heater needs repair. Check out these specific issues to see what might be causing more moisture in the air.
Turn up the Heat
If your home is somewhat warm when it's cold outside and the heater is on low, that can lead to condensation on the windows and increased humidity in the home. When warm air touches cold glass, condensation forms because the cold glass draws out moisture vapor from the air, causing it to condense. However, if you turn up the heater a bit, you could get rid of that moisture through two mechanisms. One is that the heater itself will start to draw moisture out of the air, and the other is that the remaining condensation should evaporate more quickly if the air is drier.
Your Cooking Skills
Have you been cooking more on the stove, lately? If you've been having a lot of soups and other warm, liquid-filled dishes, then you could be adding steam and thus moisture to the air just through that. Try cooking something else for a couple of days and see if that solves the problem; you may also want to adjust the appliance you use, such as using the microwave to cook things more quickly (and thus release less moisture into the air).
Your Shower Habits
If you've been taking longer showers with hotter water, too, that extra vapor can lead to increased humidity, particularly if you aren't ventilating the bathroom completely. Remember to turn on the fan if you have one; otherwise, open the window a crack when you're done to let the steam out. If you can open the window during the shower, that can help, but don't do that if people can look directly in the window and into your bathroom, of course.
Your Heater May Be Failing
If none of these work, and the weather itself hasn't been unusually humid lately, then you may be looking at a heater failure. If the furnace or heat pump is not working as efficiently as they should, then they could be removing less moisture from the air. Contact a heater repair company, such as Glendale Heating & Air Conditioning, soon because, while some might prefer more humidity instead of excessively dry air, that extra moisture can do some damage to walls and ceilings.