Hi, We're hoping to buy a used Harman Mark III, and I just have a few questions. What should we look for when we go to look at it? Is $800 a fair price? Will it heat a 3000+ 3 level house if its placement is on the lowest level. House does have ducting, thinking of creating a venting system for the Harman. I'm not too concerned about the seams, but are there other problems to look for that an older Harman may have? Thanks in advance for any input.