I need to educate myself for a possible purchase. I saw a used WM 4400 locally for sale. I have not called and asked questions yet, and that is part of what I want to find out here. What do I ask? I have heated to some extent my house with our higher efficiency fireplace since we owned the house, but we cannot sustain a night-long fire, and it uses wood inefficiently. I have considered an outdoor boiler for some time. Our house is 3000 sq ft plus the basement. We did put regular pex in the floor of the basement and garage when we built the house....but not the oxygen barrier type. Ideally, I would start with a heat exchanger, and work my way into perhaps using the floor heat pex and even getting some hot water as well. What do I look for? What do I ask. Any pitfalls? It appears to be in excellent condition from the outside. I was not able to look inside the box as it was locked. They are at $3500 obo, which seems high for any used outdoor boiler to me considering the possible expense of replacing parts that may not be in good shape at this point. But there is the "obo". Also, what are the pro's and con's of this brand and model? Thanks in advance for any help. I need it!