Blue, be sure you have the right model numbers here. The Classic CL4436 model was discontinued in 2005 and replaced in 2006 with the CL5036 still produced today. It was a larger unit than the CL4030 offered today as well. All CB furnaces have a data plate located on the front face above and left of the door. The manufacture date and model number would be located there. A used boiler value depends on the condition of it. Is the firebox in good condition or is there metal pitting or bad corrosion in the firebox? If it appears in good condition it might be worth up to $2,500 if it is a CL4436 which would mean it is at least 8 years old. If in bad condition you may want to avoid. You could buy todays equivalent sized CL5036 new for around $6,500. If it is the smaller CL4030 model it would be worth less and I don't think it would not be large enough for what you say you want to heat. I'm guessing you may be pushing the higher end of the 4436 model range. Neither of those models are the newer low emission models. Those would be Eclassics. Not sure what your Mass requirements are regarding buying used boilers. Does it include any pumps or exchangers?