Runs with Bison
Member
If you do NOT need an expansion tank, there is no benefit to installing one, and it does NOT make the heater last longer in any case. There is no functional problem with the flexible connectors.
The first question is does the OP need one? That is only answered by determining if the system is closed in some fashion. If it is a well with a pressure tank, then no. If the OP is on municipal supply, then there is a good chance that checks already exist (or will be added later) that will prevent backflow into city mains. In that case the OP probably needs an expansion tank. Either that or rely on *something* acting as a relief valve somewhere after showers/baths etc.
I've related in the past how I learned about this the hard way when I changed out toilets. One of the old toilets was leaking down then the pressure spiked during water heater recovery phase. I had checked with a tattle-tale gauge before and it topped out at 100-120. But once the toilet was gone, the pressure spiked all the way to 150 and the T&P was the relief, as seen by puddles. I sure as hell wouldn't want that happening over my head at least once a day.
As far as it whether anything will last longer with an expansion tank (meaning milder pressure cycles), I have developed some respect for the way corrosion concentrates at the more highly stressed locations in metal...and I've seen plenty of water leaks. (Including recurring ones in bends of hot water lines.) Higher pressure = more stress and larger amplitude cycles. Water heaters fail through a combination of corrosion and being unable to withstand the pressure that the could previously withstand, resulting in leaks. While I usually don't get too concerned about pressure cycles in steel pressure vessels, some of my mech. eng. colleagues have been much pickier about it with regard to fatigue failure in carbon steel process equipment...at right about the same cycle count I would expect from a water heater to hit in 10+ years of operation.