Whenever a gas furnace is not heating enough to meet your household comfort level, that's a problem. Actually, we should say that it's a "problem" in mild weather. When it happens in the middle of a winter blizzard, it becomes an emergency.
What to Do When Your Gas Furnace is Not Heating Enough
When it is cold outside and not much better inside, there are some things you can do. First, check to make sure someone didn't turn the heat off. Yes, that seems ridiculously simple. You would be horrified if you knew how many HVAC techs made service calls when the fix was something ridiculously simple. However, let's assume the problem is not that easy. What could be the problem?
Air Filter
Yes, of course, you check and change your air filter regularly. You're not one of those people. But, just in case, check your air filter. A dirty filter can put a real strain on your furnace, and significantly impact performance. If you find a dirty filter, change it. That might be enough to solve the problem.Air Flow
Check your vents to see if some are blowing much less heat than others. That can happen when there is an obstruction somewhere, a major leak, or a complete break in the ducts. You can also inspect the outside of your ducts for obvious cracks or holes. An obstruction that you can reach is easy enough to remove. Other problems may require a professional service.Dirty or Misaligned Burners
Dirty or misaligned burners can significantly impact performance. Unlike the other issues, we do not recommend you inspect the inside of your furnace. That job should be left to trained, professional service techs. You could void your warranty or seriously injure yourself. Because, it's a gas furnace folks. There's literally a fire in there. So, if you suspect the problem is not the filter or the ducts, get a service tech to check the furnace itself.