I am planning a revamp on the pool equipment. Plans are to convert to SWG, install acid injection system, replace diverter valves and maybe the teledyne laars one series 400,000 BTU heater also. How effecient is this series? should i replace it with something more modern? if yes, can someone please advise on which heater to buy? I am looking for most reliability and efficiency to keep heating costs low. I will mostly be using the heater to heat up the spa rather than the pool.