Sure, modulating boilers save energy. But consistent temperature control also means more comfort.
The important part of modulation is that if you need just a little heat, you burn just a little gas. If you need a lot of heat, you burn a lot of gas. And the valve will vary the amount of gas for any demand in between. Modulating can go down to as little as 25 percent of full firing rate in American boilers, and as little as 1 percent in European boilers.