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Discussion Starter · #1 ·
I plan to install a water heater in my boat. It never had one, but I can use a storage bin in the engine room. A 6.5gal will fit, but just. A 5 will be easier to install, leave a little storage space. This will use a heat exchanger, not electric. I plan to cruise the boat south in the fall, then spend some time aboard over the winter. She has 200 gallons of fresh water and a pressure shower already. So, if you have a 5, is it enough? Do you wish for more? Or did you install a bigger one and wish you had the space back?
 

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Practical sailor did a comparison review of these a couple years ago. Anyone w a subscription can get to back issues. One of the things I remember from reading it was that the heat exchanger option had a very quick recovery time, allowing for smaller tank vs shore power electric. I've got an old five, but never use as I'm restricted to day or weekend sails by job/family.
 

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I'm with those above;the largest possible.
However, a word of warning, the engine heating will take the water to 180+or- (whatever your engine runs at) which is dangerously HOT so be very, very careful.
 

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Dec 2013 issue, if you wanted to get a copy. You can get a premix valve added to deal with the superheating that comes with the exchanger off the engine, which appears to be a very recommended addition.
 

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Discussion Starter · #9 ·
Thanks for the constructive replies. The boat doesn't have a shore tie, this will be strictly on heat exchange. The units I'm looking at are Isotemps by Isotherm. They come with mixing valves. Mostly I'm concerned with a warm shower for my wife while anchored, and for myself too in cool weather. I very rarely dock while cruising, and when I do, we shower ashore.
 

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You ask about 5 or 6.5 gallon. Not much of a difference. Go for more if you have room. Hot water is a rate issue. Bigger does not mean much if you can't keep the tank continually hot. Since the temps are high you use little at a time.

Watch out for the Very hot water, These tank are poorly temp regulated as mentioned above comments. I mean Really hot.
 

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I agree. Not much difference between 5 and 6.5 gallons. Enough for a (very) quick shower or two and washing few dishes.

When cruising in the summer, I supplement the hot water heater with a solar sunshower.
 

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What temp do you have it set at? We used to have a boat for 2 couples and we had a 12 gal. We did just fine with it.
When I'm on AC shore power, the temperature is set at 105 degrees, but it gets much hotter when using the engine, somewhere around 125 degrees. Unfortunately, the heating element just fried last fall, so I'll have to crawl into the engine compartment to replace it. Damned I hate being claustrophobic.

Cheers,

Gary :cool:
 

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Mermaid Hunter
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However, a word of warning, the engine heating will take the water to 180+or- (whatever your engine runs at) which is dangerously HOT so be very, very careful.
Dec 2013 issue, if you wanted to get a copy. You can get a premix valve added to deal with the superheating that comes with the exchanger off the engine, which appears to be a very recommended addition.
In this day and age, an anti-scald valve should be considered mandatory. It doesn't add much cost or complexity to the install.
Capta and Gary are correct - the thermostat on the water heater doesn't affect the heat from the engine on any water heater I have seen. Whether you call the device a premix valve, an anti-scald valve, or a tempering valve (they all mix cold water in with the hot water from the heater to deliver water at no more than a preset temperature) it is a good idea. Look carefully as not all water heaters have one out of the box.
 

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I'd go with the 6.5 and be done with it. How much "hot" water you need depends on how long you shower. How hot you shower, how hot you let the water in the tank get...a lot of variable stuff. And if you have company one weekend? Right, needs more. Many folks for many years set their home hw heaters set at 160F to get "lots of hot water" and scalds were just accepted as normal. Today? Building codes often require an inspection when they are replaced, and a setting no higher than 125F. Scalds are not acceptable any more.
So why debate how many angels can dance on the head of a pin? Just roll up the carpet and give 'em all the room you've got.
 

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Rafiki 37
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Thanks for the constructive replies. The boat doesn't have a shore tie, this will be strictly on heat exchange. The units I'm looking at are Isotemps by Isotherm. They come with mixing valves. Mostly I'm concerned with a warm shower for my wife while anchored, and for myself too in cool weather. I very rarely dock while cruising, and when I do, we shower ashore.
I have one of the SPA from Isotherm. Works a treat
 

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Super Fuzzy
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Ours is 50 litres = US 13 Gallons. Wouldn't want it any smaller. I know that fresh water on board is a valuable commodity but with a watermaker and 500 litres storage we don't have, or at least havn't had any problems keeping tanks topped up. This is acknowledging that we havn't really gone off the beaten track.
 
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