I put in the AT3500 which has been replaced by the AT3900. It is their mid size unit. I put heat vents in the main cabin,the head and in the forward cabin. The air intake is in the main cabin as well, not outside. I bought the unit from Binnacle in Halifax during an online special. Webasto had very good information on their web site re sizing and installation. I believe that the installation manual is online. I bought the complete installation do it yourself kit but ran short on a few items. Brewers in Portland sell Webasto I think. The mid size unit was borderline for our boat according to literature but I can tell you that it is more than sufficient. We set the thrmostat just past half way and cabin temp is around 72 deg F. Set it higher and you roast. Great in summer as well in foggy weather as the heater keeps the air dry. Gear actually dries out.
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