I have a RayPak water heater that is about 12-14 years old and does not ignite. I took off the covers and assessed that it may not be worth the effort to fix. It is the largest of the 4 RayPaks that are sold in the 2100 series, 400k btu. They make a 206, 266, 336, 399k btu unit for natural gas, for a replacement. The one I have is plumbed to be able to heat the pool and/or the attached spa. So that is why I believe they used the biggest in that series, so they could heat the pool when wanted. The heater/spa/pool came with the house when we bought it about 11 years ago. The heater was fairly new looking, so I figure it was a few years old when we bought it. So that makes it 13-14 years old at best. Well, heating the pool with ng is really not something we do, ever, so I'm thinking that the heater does not need to be the max size in that category. So how many gallons is the spa? It is average in size, and certainly not bigger than usual. So the big question is, how big should I get for the replacement? We are located in San Diego, which is fairly mild. The spa runs on the same pump that the pool filter works on, so that cannot really change. Also I don't think I want to change any of the piping, as the new heater has the same footprint and hookups as the old one. But am I correct in that the heater was picked out for heating the pool? Or are the heaters just plumbed that way for convenience? If I remember correctly, the spa would take a max of 45-60 minutes to heat up previously, at winter temps....50 deg?