Well water; 86-gallon pressure tank (installed in 2009); using a Rinnai tankless water heater.

Hi Nhsherr...

Standard water pressure is between 40-60 PSI, but every system is different.

To determine your pressure go out to a home supply store and purchase a hose bib pressure gauge (see image) and use it on an outside faucet.

You'll have an exact answer after that, OK?

Back to you...

Mark

Just to clear this up, are you asking about water pressure, or the precharge pressure in the pressure tank? If you are asking about precharge (air pressure) in the tank, it is the same for any size tank on a well system. Air pressure in the tank should be set at 2 psi below pump cut in. Make sure to measure the pressure with pump off and all water pressure drained from the system. So, if your pump cuts in at 40, you should set the precharge of the tank at 38. Hope this helps, and if I misread your question, just let me know and I will try to help further.