Thanks Pool Clown. This is over my head and I have no idea what you mean by gas reserve, so I will give your information to my husband. There are three homes on our gas well and we have never had any problems with it.
I'm sure you have heard the phrase: going to the well one too many times. Your well probably has a BTU rating. How much gas it can supply in terms of volume. Just make sure that the heater you get won't over burden the well.
Having said that...
We called the dealer we bought pool from and asked what size heater we need for the 30 ft. round. They said 150,000 btu. My husband has doubts that that would be large enough. ...While 150K may be "properly sized" for your pool, a larger heater may give you more of what you are looking for in terms of heat rise over time. I have a heater that is way oversized for the pool but the time it takes to heat up is a fraction of the time a "properly sized heater" would take. And it is cheaper to run (cost of gas) because although it uses more gas (say per min.), it too only has to run a fraction of the time to achieve the same result.