Sizing Secondary Pump for Replacement Boiler

Mpls_Matt

All,



Obviously I am an amateur for asking such a basic question, but I could really use some help with this.



I've basically settled on the Triangle Tube Prestige Solo 110 to replace my very outdated cast iron boiler.  The current system is a single series with cast iron radiators and a Bell & Gosset 3 piece Series HV circulator.  The PS110 comes with a Grundfos UPS 15-58F-FC primary pump.  How do I size the secondary pump to run the secondary circuit to the cast iron radiators?  I have no idea what the system pressure or flow rate of the current system is.



A second question is how do I size the expansion tank if I don't know what the system volume is?



If this helps, the house is roughly 1600 square ft.



thanks for any help,

Matt

Alan (California Radiant) Forbes

Pump Sizing

You don't need a secondary pump if you only have one zone since the large flow will safely pull all the heat out of the boiler's heat exchanger.  Use the Grundfos pump; remove the B & G.



What is the size of your supply and return pipes on the boiler?  If not larger than 1", use a size 30 expansion tank which is one up from the smallest size, size 15.

Mpls_Matt

Pipe sizes

Alan,



Thanks for the help, I appreciate it.  My single circuit is split into two pipe runs that run on each side of the house, prior to the split at the boiler the pipes are 1" 1/4"; but after the pipes split they are 1" from there.  So, I'm guessing you're correct with the size 30 tank.  The cost to go up to a size 60 tank isn't a lot more; is there a downside to just putting a really large tank in to make sure you have enough volume?  Can you have too large of a tank?



Also, any issues with the freeze protection feature if I only use the one circulator?  It seems to reference this in the installation manual that you may have issues if you don't have a primary/secondary system.  Or is there nothing to worry about here?



Thanks,

Matt

HDE_2

whoa

Are you sure its a true series system? Thats a bad design for CI rads and would be rare.

I seriously doubt the PS110 boiler pump could handle the split, multi tap radiation system that required a HV circ previously

You better get one sized for you, I would help but so much more info is required

Tanks are sized on BTU and SYSTEM VOLUME, guessing the tank size isnt a smart move, but a # 30 would be a good guess.