natural gas furnace?

Question

why does my natural gas heater blow up cool air from the vents? the temperature gauge rises after awhile shows that its heating the room .

Answer 1

The blower on a gas furnace comes on after the heat exchanger reaches a predetermined temp. The burners come on and then heat the heat exchanger up to around 110-125 degrees before the blower kicks on. The reason you feel cold air at first is the furnace has to displace the cold air in the duct work first. After the ducts are warmer you will notice the air is warmer. The blower will also continue to run after the burners shut off for about 60-90 seconds. It does this to blow any residual heat from the heat exchanger into the house. Maybe you have a heat pump attached to your furnace as well. If you do the air from the furnace will seem cool to the touch. The heat pump will run and heat the house before the gas furnace runs its burners. If you are in a mild climate your furnace may not use the gas at all. Heat pumps have what are called balance points. Meaning when they reach the balance point they are no longer able to pull any more heat from the outside air. This happens when the temp outside gets very cold like in the teens. Then your heat pump will lock out and the furnace will fire up its gas burners to heat the home. You will notice the heat coming out of the vents to be very warm at that point.

Answer 2

Fter reading the answer before mine. I can see that many do not know what the are talking about. The reason for this is simple. When the burners light, the blower does not come on until the exchanger reaches a certain temp or untill after a time delay start start the blower. But what about that stagnant air that has sat in the ducts and cooled down since the last heat cycle. That air between the furnace and duct outlet has gotten cold and must be purged out as the blower starts. There is not much you can do about it. Is the duct insulated well? When the heater/blower turn off, the warmth in the duct will dissipate rapidly if the insulation is not sufficient.

Answer 3

The fan is probably programmed to come on before the heat builds up fully and to stay on awhile after the thermostat turns the burner back off. Obviously it's not blowing cold air during the middle of the heating cycle or the room would never get heated and the thermostat would never turn off. If one room is a lot different from another, you might look into the reason for that.

Answer 4

If it is a high efficiency furnace (which I believe it is), it is working a designed. In order to achieve maximum efficiency, the fan will blow immediately. This allows the use of all warm to be used. By not blowing until the air is warmed to the temperature desired, a good deal of fuel is used before the heating begins.

Answer 5

It is designed so that the blower will come on first before the heating element lights off. The reason of this is two fold: First is to purge out any gas that may have accumulated in the fire box to prevent an explosion or fire: Second: to save the fire box from over heating and shortening it's life. The blower will also stay on a little while after the flame goes out to cool down the fire box.
Originally that was used only on electric finances to save the heating elements from over heating and burning out. But the newer gas finances are also employing it to extend the life of the fire box. In gas finances you will hear it called the purge cycles.

Answer 6

It hasn't been all that cold this season. First check with a secondary thermometer. Verify temperature. If it reading right try a sweater.

Answer 7

sounds like duct work not insulated good. cold pipes fill with cold air in off cycle

Answer 8

ummmm.....maybe the gauge is broken