Unless you are living in a modest temperate climate without many changes in temperature, you need a furnace to heat, cool or possibly dehumidify your home on a very regular basis. In the case of heating your home, the furnace creates the heat, and the blowers push it throughout the duct system of your house. If you have central air conditioning, it is connected to the furnace.  It creates the cool air and the same system pushes it to all the parts of your house.

Sometimes, you may notice that while you are still getting heating or cooling, it isn't enough, or it isn't reaching the upper floors enough. This is a case of not getting air or adequate air from your furnace. After examining your furnace and ensuring the pilot light is lit, and that it is indeed producing heat, there may be several reasons to explore.

1) A blocked furnace filter

Your furnace has an air filter, which may be a disposable version or a permanent version.  In any case, this filter needs regular cleaning or changing. This is needed even more frequently if you have pets, or a home business or hobby that creates a lot of dust or other air pollution. These pollutants can get into the air, and eventually invade the filter. Removing and checking your furnace filter for heavy debris or blockage should be easy enough. Clean or replace the filter, and maintain it regularly. 

2) A broken, dirty or undersized blower

The blower fan housed within your furnace is powerful, but ensure it is powerful enough for your home. A larger two-story home will need a larger, stronger blower than a small bungalow. A dirty blower may run slow as well. And of course, a broken fan belt or motor on your blower will put it out of service. If you have heating and cooling running through your furnace, it may be dirty, blocked cooling coils.

3) A blocked, dirty, collapsed or disconnected duct system

If the duct system in your home is blocked, either by heavy debris, an internal collapse or a previously undetected disconnect within the ductwork, you will have no or inadequate air flow from your furnace. When you are inspecting the furnace and heating systems, don't forget to look in the ducts for any type of blockage. If cleaning your blocked air filters solves the issue, then your problem is solved.

If your limited air flow is due to your duct system or blower, you will need a qualified HVAC technician to manage the problem. Contact a company like Bristol Heating & Air Conditioning for more information.