Steve, Note: In several places I mention 'heating season', yours may be different from mine, since you are at a different 'latitude'. For me a heating season is November through March, plus maybe a bit on each end . <<Did you buy your system from Sure Marine?>> Indirectly, yes. I had a local friend ('boat maintenance' person) purchase the parts, as he was able to get them at a better price than I could from Sure myself. Not all parts were purchased from Sure, only the furnace itself, the 'MSR' heaters, wall thermostats, some relays, the exhaust piping (3" SS), and a few other things. The rest of the hydronic parts, i.e. tube fin, expansion tank, air purger, poly tubing and fittings, etc, was purchased through a friend that is a plumber (again for cost savings). I did purchase the crimping tool that is used for the rings user to secure the poly tubing to the copper fittings. If you have a machinist friend, the crimping tool could be made from a standard pair of bolt cutters, at a considerable reduction in price! I could help you with the modifications you would have to make to the bolt cutters. <<very few circulator pumps will make it through more than one heating season Very interesting data. I've not yet researched the pump issue. I'm a little surprised that the pump life is so short. Centrifugals are inherently pretty reliable, so long as the pump is selected to match the continuous duty cycle required.>> It is not the pump itself that is the problem, it's the DC motor driving it. It seems that DC motors have a life expectancy of 3000 hours or so, and by the time it's run that long, either the brushes are worn out, or the commutator is worn down enough that it begins to 'eat' brushes at an alarming rate. I tried a system that had a motor with replaceable brushes, that one lasted two seasons, then started eating brushes. Even with the replaceable brush motors, you will spend $15-$20 bucks for a set of two brushes. My first pump lasted for a heating season and and a half. It crapped out in January, on a nice cold night (naturally!). Let me tell you the Admiral was not happy when she discovered that that fans were running, but no heat was coming out. It was no fun changing that pump out in the middle of January! After that I changed out at the beginning of the season, that's why I say they last 1 season. <<Could you please tell us which brands of DC pumps failed for you? And which 12VDC pump you chose for your parallel scheme?>> The pump that was recommended by Sure at was the Johnson pump. That one has a sealed motor (no replaceable brushes), and it will last for 1 heating season. When the first one failed, I simply replaced it with another of the same make. After the second failure I had Sure make me up a motor/pump combination that had replaceable brushes, that was good for 2 years. Then I tried some off-the shelf solutions that were not much better. 2 years ago, I 'engineered' the parallel pump solution, and that has worked out fine for us. <<I've been particularly focused on your zonation scheme. This is one of the things we would like to do. The specific problem on a cat is you have so much real estate to cover. Plumbing one loop around the boat takes a LOT less piping than separate loops for our 5 zones (the A/C is 5 zones). Given that configuration, how do think the "zone by fan motor" approach will play out?>> What about a loop from hull 'a' to hull 'b' with a manifold in both hulls creating the required zones? That you should be able to do, and still only have to bear the cost of one circulator pump. If you simply use one large loop, I don't know how you would 'divert' the water flow through to a heater unit without having a small pump for each unit (they should be in parallel across the supply and return, not in series). With the 1 1/2" manifold with 3/4" risers, presuming the pump has enough flow, it will cause the water to naturally divide across the 3/4' outlets (I can also 'trim' the flow through a zone using the valves on the manifold). Not being familiar with what's between hull 'a' and hull 'b' on a cat (routing spaces, etc.), I cannot offer too many suggestions. <<Could you estimate the window area that you are demisting?>> The pilot house has 3 windows in the front, each about 30" wide by 28" high. <<Jim Schimke is recommending plastic tubing by "Wirsbro", but hasn't given me the details as yet. Is this the one you mean?>> don't know for sure, I recently observed it being used in South Carolina in a new house. Cheers, +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Anne & Henri Monnier m/v Sea Flat (50' Ocean Alexander Trawler) sea_flat@mymail.com http://www.seaflat.com +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+