Tankless Gas Water Heaters

Install in well-vented space and get a CO alarm.


I recently acquired a project boat, and the former owner had purchased a tankless propane water heater that he was planning to install on the boat. Any comments, considerations, or warnings on installing such an item on board?

Steve Horinek
Tropic Whisper, Irwin 42
Fort Myers, Fla.

Tankless propane water heaters carry serious risk of causing carbon-monoxide poisoning or oxygen depletion when mounted in a tight or sealed space. Because a boat is more tightly sealed than a shoreside home, the carbon monoxide is more likely to become trapped. Multiple boater deaths have been attributed to tankless water heaters, and several brands have been recalled over the years-among them Wolter Water Heater, Paloma, and Rheem-Rudd-because they posed a carbon-monoxide poisoning hazard.

That said, you will find tankless propane water heaters on some production boats, but it is buyer beware, in our opinion. Where you mount the heater, how it is installed, and how it is vented are of critical importance. Weve heard of boat owners mounting them successfully in vented spaces such as cockpit lazarettes, galleys, and anchor lockers, and many install them with heat shields. For extra precaution, you could run the water heater on a propane system separate from your stove, and rig it with a water solenoid that opens when the propane solenoid opens so the propane wont flow unless there is water flowing.

If you decide to install the tankless water heater despite the risks, you should first be sure that your heater hasn’t been recalled. We also recommend investing in a quality carbon monoxide detector like the Fireboy/Xintex (PS, December 2005), and always keeping a hatch open in the shower when using the heater. Also, check out our recent blog on inspecting marine systems for propane leaks (Dec. 30, 2013). It wouldnt hurt to look into your other water-heating options as well; youll find a good sampling of whats available on the marine market in our December 2013 water-heater test.

PVC bilge lines

I am thinking about replacing the hose for the bilge pumps and was wondering about using PVC pipe instead of hose. Have you ever seen such an installation? As I understand it, I should get better flow due to less resistance, it should last forever, and it would probably be cheaper than using hose. Thoughts?

Lloyd Herman
Rendezvous, 1987 Nonsuch 30U
Port Washington, N.Y.

The American Boat and Yacht Councils standards do not address rigid PVC plumbing in bilge systems. But plumbing must be able to withstand temperatures as low as 40 degrees below zero, and it must be supported so that it would not fail under stress. All joints have to be able to withstand this as well.

We agree with past PS contributor Steve DAntonio (www.stevedmarineconsulting.com), whose plumbing durability test is a good rule of thumb: Any plumbing components that could lead to flooding in the event of a failure must be able to withstand being stood upon. If I can’t stand on it without worrying about causing a failure and flooding, its simply not rugged enough, DAntonio explains in his blog. Many PVC components and some metallic ones wont pass this test.

The plumbing must be supported so that it wont crack or split when you step on it or some blunt object comes in contact with it-as may happen after a knockdown, when stuff is flying around. Flexible hose is pretty impervious to that sort of thing. And then there is the risk of the pipe splitting if there is water in the line when temps dip below freezing, and the headache of finding hose-PVC pipe sizes that match.

Also worth considering: Each turn in the plumbing run will add resistance, and with PVC pipe, youre likely to need more turns and connectors. There are plumbing tables to calculate how much head pressure loss each elbow, etc., puts in the line, but basically, each fitting you add is the equivalent of adding a length of hose.

Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida.


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