[Shop-talk] Hot air furnace parasitic loss

[Randall]

> > Probably what you are hearing is the control transformer in 
> the furnace.
> > Your thermostat  and controls runs on 24V. There will be a small 
> > amount of eddy current loss in the transformer, but that's about it.
> 
> Probably 10 watts or so.  (If it's old, maybe lots more.)  

That seems way high to me.  Whatever it dissipates is converted almost
entirely to heat; and 10 watts into something the size of a control
transformer would cause it to get quite warm even in free air.  Mine is some
40 years old, and just barely gets warm to the touch.  Might be 1 watt, but
I doubt even that.

Randall