Expansion tank pressure setting

[trashmn24]

I am building a new, one-zone, baseboard hot water heat system in our basement. Mechanical room is also in basement and the baseboards are on a closed loop, with only about 1 to 1.5 gal of system water heated via heat exchanger from a Takagi heater (also for DHW). 30 psi relief valve. Grundfos 15-58FRC circulator.

I bought a Watts PLT-5 expansion tank. It says for potable water and the factory precharge is 40 psi, which to me seems high for use in this system. I know there are non-potable versions of tanks, but hey, I got a good deal.

My question is can I use this tank? What should the air charge be set at? Do I just get a good pressure guage and bleed air from the valve until it's right?

What happens to system if I leave it at 40 psi? No expansion allowed?

Thanks,
Dave

[Ed Imeduc]

All of the tanks for the hot water boiler come at 12 psi.
And if you left it at 40 the PR valve goes go off at 30 psi.

ED ;)

[trashmn24]

Thanks, Ed ....

So, can I use the tank I bought already and use the Schrader valve to reduce the precharge to 12 psi? Or should I buy a tank correctly preset for the application?

Thanks!
Dave

[Ed Imeduc]

Try it why not

ED ;)