Hi everyone, great forum you have here! I just picked up my new k8 boiler last week and am looking to complete the install over the next week or so. I plan to tie into my existing ductwork with a water/air heat exchanger and use the existing fuel oil furnace blower to distribute heat as the house is quite large (4500+ sq feet) and radiant is not in the budget for most of the house. My first stumbling block is how to size the w/a exchanger. Oil furnace is 180k btu input, and heats the house very well, but to the tune of over $900/month in fuel, just to maintain 64 degrees. Would a 180k btu exchanger be a good ballpark? aside from a circulator pump and expansion tank, most everything else can be purchased locally I believe. I would like to order from pexuniverse asap so I can complete the install between friday of this week and next wednesday. I have been reading here for the past week or so and gained a lot of insight, thanks again for a great forum! Any help on the heat exchanger issue would be greatly appreciated!