Installing Lochinvar Knight 500 question on system circulator

Riverrat35

I'm installing Knight 500 on old steam radiator system.Manual gives boiler circulator specs.How do I size system circulator? Should it match specs of boiler circ ?

Doug_7

System Pump Size

I assume you have one system pump and zone valves ?

System pump needs to be sized to give you the design Delta T you want between the system supply water temperature and return water temperature on the coldest design day or at full boiler capacity.

Equation is: GPM = BTUH / 500 x Delta T

The nominal maximum BTUH of the system is 500,000

The maximum Delta T you want is about 20* F at full boiler capacity. This is a common design Delta T.

Plug this into the equation and you find that for a Delta T of 20* F at full boiler capacity you will need about 50 GPM of system water flow. This is bigger than the boiler pump which runs at a much higher Delta T.

Need to calculate the system pressure drop at 50 GPM to get the required pump head and pick a pump that will give you that combination of flow and head.

Doug

Riverrat35

thanx Doug..yes, one pipe with zone valves.also i should have mentioned that the old system was allready converted to hot water.system worked ok just needed a new boiler.you answered my question and i underdtand the formula.ihave the specs for pressure drop and feet of head.thanx again