ODR

The benefits of Outdoor reset have been discussed here previously, so you might benefit from doing a search on outdoor reset and Tekmar or Honeywell.

Basically, the concept behind ODR is that changes in exterior temperature will require a change in the heating and cooling of the indoors as well to ensure that the house stays at a constant temperature. It's close in concept to using cruise control on a car, except that ODR usually looks several hours back and uses some algorithms to make predictions about the future, i.e. as if your crusice control had a ground-radar instead of just reacting to a slow-down or a speed-up.

Warm water systems simply modulate the supply temperature up or down. Steam systems respond by firing less or more, as needed.

I imagine that outdoor reset has the biggest payback in terms of comfort and efficiency with high-mass systems. With ODR, the likelyhood that a large thermal mass like a concrete slab will overheat a room is lessened, for example. Steam systems are lower in mass, quicker to respond to actual conditions, and hence are likely to benefit less from ODR. Nonetheless, considering the cost of fuel and the cost of the control...

Plus, I doubt you wouldn't come close to the 9% minimum savings that (IIRC) Honeywell reported way back when they did their ODR testing.