My old 175K BTU natural gas heater (30 years old) is due for replacement. The gas regulator/valve is flaky and can't hold a constant burner flame anymore. Amazing that the heat exchanger has made it this long with all the abuse I put it through. Although I suspect that maybe the heat exchanger is actually clogged as the heater doesn't really seem to heat the pool very well anymore. Even when new, the rated efficiency was only 70%.
My local pool serviceman suggests a 250K BTU Pentair MasterTemp natural gas heater as a replacement. My pool is an 18'X36'X4'5" in ground oval sport pool that holds 17K gallons. The pump is a 1HP Hayward SuperPump When my family uses the pool, we like to have the water temp around 87-88 degrees. Here in Minnesota the typical swim season is Memorial Day - Labor Day.
I have read through all the heater posts on these forums. It seems like the general attitude on these forums is "bigger is better" when it comes NG heater sizing. Pentair also makes 300K and 400K BTU sizes of the heater as well. I suggested to my pool serviceman (which in turn consulted with the local Pentair serviceman) that maybe I should purchase a 300K or 400K model. The response I received from my pool serviceman as well as the Pentair serviceman is that 250K BTU is the norm for pools my size (and even larger 20'X40' pools) and that a bigger heater is a waste of money. But is that really true?
It seems to me that if all sizes have the same efficiency rating, that the amount of time that the heater needs to run should be proportional to its size. My gas meter is 15' away and is currently 1" pipe. If I go with a 300K or 400K heater, I would have to upgrade the gas meter, which I am in the process if checking if there is any cost to me for a meter upgrade.
I would appreciate hearing from all of you what your thoughts are regarding getting a larger BTU heater. Are there reliability problems with the larger sizes? Efficiency problems? Excess heat issues? Safety issues? Etc.?