Balancing valves on manifolds

If you have one loop wide open and another loop closed, a lot. An average system my experience is that you can generally squeeze about 2-3 degrees out of them while still working linearly if properly installed. For example, if someone likes to keep their house at 70 but wants the bathroom a bit warmer and the bedroom a bit cooler, the bathroom might be able to maintain 71 while the bedroom is 68-69. Anything beyond that, you're looking at another zone unless you want to screw with the balancing every time the outdoor temp changes. If you close the bedroom loop down far enough to be 62 when it's 40 outside, it'll get progressively cooler in there as the outdoor temp drops while the rest of the house maintains 70

John, I'm installing new and working through the zoning issue, upstairs/downstairs etc. I would be curious to know how you are leaning?

Flow and the temperature of heated water go hand in hand. Most often the zones in a hydronic sys are of unequal lengths as measured and computationally(fittings,etc.).

Water will flow thru the least restrictive piping circuit at a greater rate than the others. There are time when this is destructive to the piping sys. Flow rates must be within the pipe's flow capacities. To high a flow rate will erode the pipes.

There are many variables that affect the heat transfer into a living space, temperature differential, supply water temperature, flow, etc. If you shut off the supply to that zone, the temperature in that room will eventually reach equilibrium with the environment. So flow has a lot to do with heat energy transfer into the living space. There are too many variables to tell you what the degree difference will be with balancing valves, except to say the less the flow, every thing being equal, there will be less heat energy transfer in to that living space.

One uses balancing valve to balance multiple circuit in a heating sys to the desired flow. Some under performing circuit may benefit from a higher flow rate and the reverse is true, also.

I am a big believer in balancing valves, they give you a visual indication of flow, which gives you a more consistent heat energy output thru out the building.