Furnace blowing not warm air
We just moved into a single story Ranch house about a month ago and have noticed that the furnace runs for very long periods and furnace blowing only very cool air. Kind of like a spring day.
We looked at the board and switched the fan from hi to low and the vents now blow out a little warmer air, but only a little bit more than cold air.
Also,
We have our thermastate in the Hallway and right abouve that is the Return Air Vent. And right beyond that it feels like there is a wall of cold air and the whole back of the house is freezing.
Is there anything that we can try to get the furnace to pump out hotter air?
I am not sure of the difference between the 2, but there is a hole in the wall on top of the hallway, directly across from the vent.
Also, there is something directly left of the vent in the wall about knee high. What is this?