Hello All, I inspected a 14 yr old Tempstar gas furnace today and always feel the draft induced fan motor for operation and heat. In my opinion it was very hot “154 deg” with my laser thermometer! The furnace has been running a while, but never came across one this hot. I did visit my parents for dinner and their 13 yr old York furnace was a close 151 deg. Is this pre-mature failure or a normal occurence.
Thanks in advance,
Chris
Heat kills motors and heat comes from current. Amp the motor out while it is running and see how much current it is drawing. If it is drawing above rated levels, the motor will definitely heat up (for example the bearings might be dragging, thus loading up the motor more than normal). I don’t know if there is a nameplate on the motor, but sometimes the manufacturer will give you enough info to calculate the current, if the current is not stated. For instance if they give you the HP and the voltage you can figure out how much current the motor should be drawing. 1Hp=746Watts, take the watts value for your motor and divide by the voltage 120V and that gives you the current you should be drawing. I do not have the NEC with me, and I am not sure how low they go (I believe mine is a 1/12 HP motor), but I believe the NEC has a chart in it that gives amp draw for various HP ratings.
I made a lot of assumptions here, but I hope this helps.
Jeff, you provided a lot a good information on motors[FONT=Tahoma][size=2]. However, this is an " induced draft motor". 150° is not even close to warm for the application of this motor.
[/size][/FONT]This motor is attached to a blower fan that draws combustion (fire[FONT=Tahoma][size=2])[/size][/FONT] through the heat exchanger and discharges it out of the furnace. We can expect that under this application it would get warm.
Also, utilizing 1 hp = 746 W consumption does not work in small motors[FONT=Tahoma][size=2]. The efficiency of small motors is only about 50 to 60% because of motor efficiency. They can consume nearly twice as much current as they should in comparison to large motors to generate the nameplate horsepower.
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Excellent, more late night motor reading… And here I thought nights of late were for Electrical code! I am still trying to get my head around the AFCI requirements in the 2008 cut of the NEC.
Thanks for the info!
What should these puppies normally run at – say…… an induced draft motor on a 90+ gas furnace, then the same for an 80 furnace? Any thoughts?
Temp or Amp?
Amp is on the motor.
Temp has a lot to do with btu input, efficiency of the heat exchange, purge timing etc.