Seeing as I don't know next to anything about heating/ac, I decided I'd post here to see if anyone had any idea.

The setup is some old heat pump/furnace/water heater/etc, which all of a sudden at around 3:00am this morning decided to make a VERY loud noise. I had to shut it off (the furnace is a gas furnace, if that helps) using a switch that was installed for that very purpose, as the unit is rather old but generally still works.

Basically, the motor makes an extremely loud running noise, and I'm not too sure what it could be. It's as if a car has started in the basementm, the noise is that bad. I'm going to try to switch it on again tomorrow morning, but I was wondering if there was any danger to leaving it unpowered other than maybe not having hot water. The pilot light is still on, so it seems to be going okay.

Thanks.

Shutting power off to the system, is little different than turning the thermostat up too high to call for cooling. It should be safe to leave it that way until a repairman comes. This loud noise, is it the sort of screech that sends you to have your brakes relined? If so, it may be a fairly easy repair to the blower that circulates the air. If it is more of a pulsing sound that sends you to a muffler shop, it is a compressor failing, requiring a licensed HVAC repairman. Compressors are outside in an A/C system, but I guess one could be inside for a heat pump.

Having the same issue, I took a hvac course few years ago so I'm by no means a expert, but I can trouble shoot most problems once I go through the sequence of events as the furnace starts up, I have come to 1 of 2 conclusions, bearings in the VENTING MOTOR (not blower with squirel cage) are shot, or inside the shroud of the VENTING MOTOR there's a alignment issue with the fan blades