Split loop

Brad White

Your little birdy is a male, therefore waxes colorful I take it.

The issue is balancing. Yes, you have disparate circuit lengths hence different resistances. The solution is to install balancing valves, at least one on the shorter of the two circuits, but I would do both. (The presence of one even on the shorter circuit and even if fully open, may be "too much" and tip things the other way.)

Either way you are not looking at tremendous differences in pressure, but control is a good thing to have.

Your pipe sizes seem fine from an anticipated flow standpoint. Pump away from your expansion tank and keep going.

My $0.02

Brad

Joe_105

I have a hot water baseboard system in my house. Right now it is two zones, 1 upstairs and 1 downstairs. The upstairs loop starts out 1" after about 5' it splits to two 3/4" loops. The first feeds two rooms for a total of about 33 linear feet of fin tube and a total run of about 65 linear feet. The second loop feeds four rooms for a total of about 47 linear feet of fin tube and a total run of about 72 linear feet. All fin tube is 3/4" copper. These two loops join together into a common 1" return. I am replacing my boiler and was always taught to put my circulators on the supply. However a "little birdie" told me that if I put my circulators on the supply, I will have an issue because of the split loop. I believe it had something to do with the shorter loop returning hotter than the longer loop. Is this the case? Of course he stated that he has run into this problem before, and everyone else I ask says I shouldn't have a problem. I am not sure what to do. I'm torn, please help.

Joe_105

I have a hot water baseboard system in my house. Right now it is two zones, 1 upstairs and 1 downstairs. The upstairs loop starts out 1" after about 5' it splits to two 3/4" loops. The first feeds two rooms for a total of about 33 linear feet of fin tube and a total run of about 65 linear feet. The second loop feeds four rooms for a total of about 47 linear feet of fin tube and a total run of about 72 linear feet. All fin tube is 3/4" copper. These two loops join together into a common 1" return. I am replacing my boiler and was always taught to put my circulators on the supply. However a "little birdie" told me that if I put my circulators on the supply, I will have an issue because of the split loop. I believe it had something to do with the shorter loop returning hotter than the longer loop. Is this the case? Of course he stated that he has run into this problem before, and everyone else I ask says I shouldn't have a problem. I am not sure what to do. I'm torn, please help.

Joe_105

So I should be balancing these two loops so they come back at the same temperature? Correct?

Brad White

Pretty much

If you assume that the amount of element is proportional to the heat losses of the spaces served, then yes, temperature is an effective way to balance things.

Flow is far too forgiving sometimes though. You can throttle the flow by half and still get 90% capacity.

But short answer, balance to water temperature if the radiation is proportional to heat loss. Balance to room temperature outcome ultimately in any case.

Joe_105

Where do my balancing valves belong? Do they go on the supply or return, before or after the circulators? Thanks again.

Brad White

On the return

of each circuit, usually. As an academic point it really does not matter, but I always put them on the return as the resistance and back-pressure helps to force air out the high vents.

The balancing valves I like to use are Macon Controls, with Tour and Andersson and Oventrop/MEPCO or Armstrong as other quality brands. Ask for multi-turn Wye-Pattern balancing valves. These have temperature and pressure ports built in, so you can use a probe thermometer for temperature balancing. Very smooth precise operation.

Have a blast!

Brad