Replies

1. 
   davidmeiland | Jul 28, 2011 08:47pm | #1

   Well, watts = volts times amps, so you need to measure the amps drawn accurately. This is very easy with a 120V appliance, because you can plug it into a Kill-A-Watt meter or something similar, and it will automatically track usage over time. It's a little harder with a 240V appliance, but there are metering devices that will handle both legs at once, and track over time as well. If you have something that runs continuously, you can measure the draw with a clamp meter, but most things turn on and off, and/or vary their draw, so you need some tracking capability.

2. 
   user-956864 | Jul 28, 2011 11:22pm | #2

   Thanks for going easy on my question. As I started to type I guess I realized that if I detailed chapters of specs I couldn't tell the whole story. You were brief, clear and effective, thanks. I've got to measure to come close to an answer to my question. How many watts does my blower fan draw?

3. 
   davidmeiland | Jul 29, 2011 12:46am | #3

   If I'm reading your post correctly, the motor nameplate lists Full Load Amps = 7.0. Tempting to say that 7A at 120V is 840 watts, but typically, it's going to draw less than FLA while running, so you really need to meter it to know what it's pulling, and you need a long enough sample time to even out any variations. Ratings don't really tell you enough.

   The easiest way to get the data that I think you want is to use something like a TED 5001, or another power meter with multiple current probes. Get your heating system wired to your electrical panel so that a couple of breakers are running the system and nothing else, and then meter the operation over time via those breakers.

   If you really want to go whole hog, you can start measuring the temperature rise and flow rate of the water going through your geo pump to the floor, and turn that into a cost per BTU. You need to buy some hardware and do some setup, but you can meter this stuff if you want to. You can get real-time readings on your screen. I'm sure someone else (Michael Chandler?) here knows more about exactly what to do.

4. GBA Editor
   Martin Holladay | Jul 29, 2011 06:43am | #4

   Rick,
   I will echo David's warning about the need to measure power use over time. Standby power usage can be large; in one study, a GSHP was drawing 45 watts continuous when it was NOT operating. More info here:
   http://www.carb-swa.com/articles/carbnews%20articles/CNFebruary08.pdf