Anyway to figure out cost per hr of a natural gas heater?

[cruzmisl]

OK, here's what and how I measured. I don't really care about how much my pool heats up, just how much it costs me to run it per hour. It's heats it up really fast anyway.
My bill is in cubic meters, no therms on it anywhere. I turned the heater on and timed the meter and this is what I got.

.05/m3 used every 20 seconds
20 seconds x 3 = .15/m3 every minute.
.15m3 x 60 = 9 m3/hr

With transport charges, storage, delivery I pay 45 cents/M3 of natural gas so....

9x.45= $4.05/hr to run the heater.

Seems low (good for me) but maybe I calculated wrong. I am not a mathemetician by any stretch of the imagination.

Thoughts? If it's correct at least others may be able to compare what a heater costs to run.