Because of this, you may find it difficult to get three or four competitive prices if you base the comparison on a particular boiler. You see, the contractors you speak to may buy from different wholesalers. If you ask for Brand A and the contractors' wholesalers stock Brands B or C or D, each contractor will try to sway you to the brand he's used to installing.
Rather than try to level the playing field by having them all quote on a certain boiler, do this: Let each contractor quote on what he thinks will best heat your home, but have each contractor guarantee the results in writing. Have them say, for instance, that when they're finished, your house will heat comfortably, evenly and with no noise or squirting air vents. Some contractors will run for the hills when they realize you're buying results instead of just a boiler, but you're better off without those guys anyway.
A good contractor will talk to you seriously about your system's problems and their solution. He'll most likely suggest things that go beyond a simple boiler replacement. There are people out there who have no problem guaranteeing results.
A final note. Competent steam contractors generally charge more for a boiler replacement than others, but these guys deliver those wonderful results - increased comfort and substantial fuel savings.
They'll never be the low-bidder, but they're well worth their price.
And please remember that to be proficient at steam heating, a contractor doesn't have to be 70 or 80 years old. He just has to be someone who's done his homework well, and who knows how to listen well to your concerns about comfort in your old house.
Respectfully,

Dan Holohan

"Plumbers Protect The Health Of The World."