Get at least three!
When we bought our home seven years ago, it had a 20 year old boiler that made steam to supply the old fashioned cast iron radiators in the home. Unfortunately, only about half of the 12 rooms in the house had radiators. The remaining rooms were unheated. As a stopgap measure, I installed electric baseboard heaters in the previously unheated rooms (mostly bedrooms). It became obvious within the first year, that electric heat and Maine winters, combined with a drafty 100 year old home, were not an optimal combination!
Extending the steam piping to the remaining rooms was considered but didn't seem practical as very few heating contractors have steam heating expertise. My feeling was that the boiler still had a lot of life left in it, so I thought it might be worthwhile to convert it from steam to hot water and install new baseboard units in all the rooms. That combined with using plastic piping (PEX) to connect the baseboard heaters to the boiler, might make it more feasible than any other alternative.
A couple of years ago, we decided to make the change. The first heating contractor came to my house and looked over the old system. I explained my ideas for converting the boiler to hot water and running new baseboard. He looked and he thought. He thought some more and he looked some more. In fact, I don't believe that he ever said a word the whole time that he was at my home. I gave him my notes and asked him to get back to me with a quote. I never heard from him again.
The second contractor brought an engineer with him. He looked at the old boiler, and said it would not be a problem to convert it to hot water. He measured all the rooms, took detailed notes and said he would get back with a quote. After a few months of calling, I finally received a quote of $21,000 to complete the project. I thought that this was quite high, especially since it didn't include a new boiler! However, it was a reputable company and I had no point of comparison since the last heating system that I had purchased was installed over 20 years ago. After making a number of calls to other plumbing and heating contractors, I couldn't find anyone that was even willing to give me a quote on what I wanted to do. I called the second contractor back and told them that we were ready to get started. They said fine. We never heard from them again.
Earlier this year, I happened to mention my problem to a realtor that I work with on occasion. She mentioned that her son was in the plumbing and heating business and that I should give him a call. He was basically a one man operation, doesn't advertise and relies on word of mouth for obtaining jobs. Desperate, but not really sure about this guy, I gave him a call and he came over to check out the boiler and make some measurements. Within a week or so, he came back with his quote of $8400. Trying hard not to act surprised, I told him that I would get back to him. After receiving a previous quote of $21,000, I had serious doubts that the job could be professionally done for $8400! However, he was willing to get to work within a few weeks and he and I were on the same wavelength about what I wanted to do.
The end result was exactly as I had hoped for it to be. We now have heat in all of our rooms. The system runs smoothly, quietly and efficiently. The contractor thoroughly cleaned the boiler, replaced some parts, installed new piping and ran new baseboard throughout the house. His workmanship was top notch and he completed the job in about 3 weeks. My contribution was to remove the old steam piping and come up with creative ways to run the piping and thermostat wires through closets and crawlspace.
The bottom line is that it took a minimum of three interviews to find a contractor that had the time, the willingness and the expertise to do the job at a fair price. In retrospect, I consider myself to be very lucky that the first two contractors didn't really want the business. The lesson I learned is that you may need to explore as many alternatives as you can, to achieve the results that you want.