Why does my heating system only blow cold air?

Question

My heating system only blows out cold air, not hot. I've left it on for a good 15 minutes to see if it will warm up, and I get nothing but cold air. I've even put it on Auto and waited some more, but still all I get is cold air.

What could be the problem?

Answer 1

Several possible issues:

1. Bad thermostat
2. Pilot light out (if a gas furnace with a pilot light)
3. Heating element out (if electrical furnace)
4. It's cold outside (if heat pump - coupled w/ #3)
5. Electronic ignition shot (gas furnace w/ no pilot light)

Without more information, that's the best guess I can make.

Answer 2

Turn off the furnace, remove the thermostat, touch the R and W wires together (as well as R and G), and then turn it back on and see what you get. If this works, then your thermostat isn't calling for heat correctly, but the fan is operating when it attempts to.

Answer 3

Are you sure the air is cold? That is to say, are you sure the air isn't just 'slightly warmer than ambient'? I've seen systems where the air blown in from the heaters was only a couple of degrees up from ambient. Couple that with the fact that it's moving, and you'd stick your hand in the airstream and it felt kinda cool.

The real test is: does the HVAC system heat the house! Try turning the heat to a few degrees above exterior temp and wait a few hours - does the house get warmer overall, or colder? If it gets cool at night in your area, try the experiment at night.