There is some circumstances where it only needs to send the amount of heat it needs. In those cases yes it can be more efficient. But for the general public and 99% of outdoor boiler installs protecting the stove with a proper delta t is most crucial.
I have tested pumps here and went down to ducmenting wood use via weighing it and moisture checking, documenting temps, and never saw any wood savings between my bumble bee and lets say a grundfos 15-58
Thats not to say that in a complex boiler system where there is in floor heating, storage tanks, and stuff like that that proper zone pumps etc arent important to the design
However nearly all of my installs are very simple, most consist of a 20 plate heat exchanger and a 16x18 coil over a forced air furnace.
Like slim was saying the other day, how many folks do we see with a cobbled up boiler system but have a 60k dollar truck
Well, all I can say is, im not sure who you all work for. Most all of my customers are trying to decide how to get through the next month, how are they gonna put food on there table next month when there electric bill is 600 bucks. So when it comes to the install, all we can do is offer them the best and let them to buy what they can afford.
I know premium lines like logstor are hard to beat, but many of my customers stagger backwards when I tell them my cheapest line sets are 6 bucks per foot. Some even leave immediately cussing under there breath callin me who knows what
So its like comparing apples and oranges.. if someone can afford mass storage, 20k dollar installs etc, then they have the ability to chase every speck of efficiency available. I get jobs like that as well, but if I depended on those to run my business, id starve the first month. I live in the poorest region in our nation.
Once again, not saying your wrong, but for the way outdoor boilers are gernally ran proper sizing of the pump to help protect the stove from low return temps is our main concern. However most dont even concern themselves with that.