Hello Fitter30,I drained the system after removing the old boiler and got about 5 gallons. I'm thinking 1.75 gallons of the proper boiler glycol would give 35%. The old stuff ran about 3yrs and had a bit of black gunk (est < 1/2 gal) which settled to the bottom of the pail. I'm guessing this is the old glycol? Still trying to understand if i need to create a secondary loop and have the secondary pump in that loop or just put it somewhere on the supply side after the expansion tank.
Question - A boiler guy said I can put the secondary pump on the return side provided I have the check valve in the supply side. This would make the pump install easier. Can you let me know.