Hydraulic separator, Closely Spaced Tee needed for single zone system?

willpar

Hello all, I am looking at replacing a very old boiler system with the Rinnai i120SN (heat only) unit. It's currently a single zone (with a split going to each side of the 2200 ft2 house) but no valves and only one thermostat. Current system is only a single pump for the boiler on the return. Do I need to install a hydraulic separator/CST in this system and a separate boiler and system water pump? Or just install the pump going into the unit? Installation instructions all indicate the use of the Closely Spaced Tee needing to be used. If so, I would need to reduce from the 1 1/4" combined return line down to the 3/4" line going into the unit. Likewise, the supply piping is 1 1/4 before the split and would need to be reduced coming out of the unit. I will replace everything else, air separator, expansion tank, dirt separator, PRV, fill valve, backflow preventer. Thank you!

hot_rod

With a hydraulic separator you will get excellent air, dirt, magnetic, and hydraulic functions 

3/4 from heater to sep

EBEBRATT-Ed

Follow the boiler MFG requirements. The modern equipment is finicky and if you take shortcuts, you can have problems.

willpar

Thanks hot_rod. Was going to keep the 1 1/4" supply line already in place and keep the air separator/expansion tank there and put the dirt separator in the 1 1/4" return line before the heater. My understanding is the wider the pipe, thus lower linear flow through the pipe the better the air separators work? I'm planning on using a Grundfos UPS15-58FC for the boiler pump and I guess for the system pump now. The low speed should be sufficient for flow spec but I'll have the ability to increase if need be.

hot_rod

Rinnai shows both their P/S kit or hydraulic sep. as acceptable piping.
The Grundfos 15-58 should be adequate, per their charts.
Pay attention to the water spec also.