Meaning amps, to run fans and circulators(for hydronic). They're trying to copy a household central heating system with various ducts or piped loops. Just trying to get the hot air through the duct work increases the fan energy needs while decreasing the efficiency of the heaters.

It seems a better design for many boats might be a single source that heats air or water to an air assisted radiator(like a bus heater) from one central location. Moving a large amount of air at a slow rate would heat a boat quickly(one grill/duct). Essentially if you can heat the salon of most boats to a comfortable warm level, all will be pretty livable throughout.

That would eliminate the extra fans, ducting or piping installation, cutting costs and labor, and add efficiency to the system while cutting it's house battery usage. This could perhaps be a middle of the road cost central boat heat system for medium sized boats.