Not too hard if you're willing to spend some time.
1) you can measure how many amps it draws when running with a simple ammeter, probably the one on your vom meter.
2) keep an eye on it for a few hours at different times of the day. record
how long it's on and how long it's off. although it sounds like a fools errand you will see that the on/off periods tend to remain fairly constant once it's been running for a few days/weeks. my adler barbour runs 14 minutes on and 20 minutes off. so i figure its running about ten hours a day. at 4 amps. so 40 amps a day.
or you can buy a recording amp meter. google
them. but they're pretty expensive for this one time use.....