Here’s a lot more detail, in case of interest for anyone who likes details…
EXCEL SET-UP
There is absolutely no problem setting up a venting system for an Excel. It just has to be done properly. It simply requires a competent worker who will do a proper job of caulking a hole through the deck, knows how to install a water hood over the vent pipe through that hole, and knows how to insulate the hot air hood which will go over the Excel.
Without knowing exactly what your boat already has, I can’t be specific about what you need. So, I’ll go through it as if you were starting from scratch.
There needs to be a metal vent over the unit that’s sort of an upside-down funnel. These are sometimes also called “air hoods” or “heat vents”. It will have a rectangular opening at the bottom slightly bigger than the unit, narrowing to a 3” or so tube at the top. If you can’t get one from the Excel supplier, you can find one that will work from many large home heating and plumbing suppliers.
Another metal tube, at least an inch wider, will go through the deck. That tube needs to be fitted very tightly to a hole cut through the deck, and caulked very thoroughly all around to prevent water intrusion. It needs to have a top cover designed to allow air to flow out but keep water from running into the tube.
The tube at the top of the vent hood is wrapped with an insulation material, usually fiberglass, and fitted inside the larger thru-deck tube. This allows the water heater exhaust and any propane fumes carried with it, to get outside the boat without hot surfaces that could burn someone or affect the boat deck.
This may sound intimidating, but it’s a job that any marine plumbing or competent general boat repair person is perfectly capable of doing.
HEAT EXCHANGER
It doesn’t really matter what kind of engine you have. A heat exchanger will work with any engine. There’s no additional load on the engine. It’s basically just adding additional plumbing that takes advantage of what the engine already does.
As an engine runs, the heat it produces is ultimately reduced by pumping sea water through the engine cooling system that absorbs the heat. That heated sea water ends up being mixed with the engine exhaust and pumped out a fitting on your boat’s transom.
All an engine-driven heat exchanger does is take advantage of that stream of heated water as it passes by. It diverts the hot sea water so that it runs through pipes in tank full of fresh water. That heats up the fresh water, which is stored in a hot water tank for when you want to use it. The now somewhat-cooler sea water continues on to get mixed with the engine exhaust and sent overboard exactly as before.
Heat exchanger water heaters often come with an additional electrical option. When plugged into shorepower, they can also heat the water in the tank just as an electric water heater in your home would.
It all depends how you choose to set up the heat exchanger. In all cases, it has to be plumbed into your water system. If you want shorepower-supplied hot water, it also has to be wired into the electrical system. If you want engine-driven hot water, it has to be plumbed into the engine exhaust system. You can purchase and set up heat exchangers to do one, the other, or both.
TRADE-OFFS BETWEEN AN EXCEL VS. A HEAT EXCHANGER
The Excel heater, like the Paloma it replaces, heats the water just before its delivered through the faucet. It therefore doesn’t need a hot water tank.
With a heat exchanger, the water in the hot water tank cools off if it’s been too long since the engine was run or shorepower was attached. In contrast, an on-demand heater like the Excel will always give you hot water (as long as you have propane). That’s why owners who sail a lot and spend time anchored or moored prefer them.
If you choose to set up an Excel, there’s no situation where you need a head exchanger.
If you choose a heat exchanger instead, you avoid the hassle of vent installation. However, the hot water tanks that they require cool off at about 2 degrees F per hour, so you lose hot water unless you run the engine or plug into shore power every day.
– Bob
I do not know how to mitigate this problem, though I expect that a very secure mounting would be an important start. Final risk is that an electric version might draw a lot of power and will require more careful management when at the dock.