I have noticed that the house I moved into has a furnace that only blows luke-warm air out the vents. I have taken off the cover to watch the furnace go through the cycle and everything seems to work, it lights up and the flames start and appear to stay on, and the air coming out is not as warm as it should be.

It could need a gas pressure adjustment to see where water column is set and to compare that with the furnace rate tag. You did not state what kind of furnace so I guessed it was gas fired.

Yeah, it is a propane furnace. How would I go about checking that.

In order to adjust the pressure you will need a special tool. I do not recommend that you as a non professional attempt the adjustment since it is propane and can be more dangerous to work on than natural gas.

Another Item that can be checked is the main burner orifice for spider webs. In the summer small spiders have been known to plug up the orifice with a web then when the winter comes the burner will not put out enough gas to allow the furnace to run properly.

My suggestion is to allow a professional clean the orifice and check the gas pressures.

If you feel like cleaning the orifice just pull the burner from the unit locate the orifice and depending upon the size of the opening use a small pin to clean it out.

All right, thanks! When I watch it though it seems like the flames are pretty big and I would think that would be enough to heat the air more than it does, but I don't know for sure since I'm a novice.