From their web site approximately 0.44 gal/hour
. That's a continuous hour, the burner typically only runs a few minutes at a time as needed.
Thanks Neil, should have looked at the web page, just being a little lazy. I have however found that just on electric elements I can run front zone on furnace and rear on heat pump. The furnace keeps the floors ok ( I don't really like $6000 socks) and so far just turn the burner on for a few hours (don't think on for 5 minutes is good) in the morning for showers. Funny thing is we keep the front (Zone 1) at 72 and bedroom at 70 and in the front on electric and rear on heat pump it appears (no science here) to work fine, which makes zero sense knowing the operation of heat pumps. My only theory is that since the front is at 72 the duck work is bleeding the return air from the font so the heat pump isn't actually seeing the 29 degree air. From researching home heat pumps years ago and doing the thermal analysis, heat pumps should be able to provide close to 30-40 degree differential from outside air. Which means the coolest it can keep a coach on a 100 degree day is 60-70, and the warmest on a 30 degree day would be 60-70. Contrary to popular belief the heat pump doesn't quit working (on its own) no matter how cold it gets outside, just can't keep coach a 70 when 0 outside, if you are happy with 30 degrees inside, the heat pump will do that at 0 outside temps.
Anyway thanks for the info, at .44 g/hr with a 5 minute on, 15 minute off (just guess) 25% duty cycle get you to .11 g/h = 2.6 g/day = 18.5 g/wk. Since the burner is only going to really be used at night you can at least double that to 18.5 g/2wk or 9.25/wk.
Actually after doing the calculations, not sure why I don't run the burner more...