Water Heater Size

My 20 gallon water heater has developed a leak after just 5-years. Probably partially my fault as I never installed an anode. Anyway, I need to replace it. What size do I really need. We are liveaboards; just my wife and I with an occasional couple as guests for a week or two. Would an 11 or 12 gallon heater suffice or do I need to stick with the 20 gallon? Thanks to all.

Howard we have too much of a good thing. The water gets too hot. It’s quite likely because the tank is too small (small boat).

With hot water, more is better.....too much is just right!

Howard: We have a Raritan 12 gallon (11 gallon capacity) and live on the boat full time. It has a quick recovery time, 13 gallons per hour with the 1250 watt element plus and integral anode. The unit was on the boat when we bought it 10 plus years ago. We’ve changed the anode 3 times. I’ve never had a larger one but haven’t felt the need for a bigger one either.

Often the price for a 20 vs say a 15 gallon unit are close. If you've got the space, 20 sounds good. BTW, some tanks are just junk right out of the factory. The term "glass lined" is a nice to have.

good insulation is better than size to a point.

went to the 8 gallon Isotherm with only 750W element and it is way better than the cheapo stainless or aluminum 6 gallon with tbe 1500W element.

If I had the room, a good 12 gallon would be more than enough and might be hard to reheat larger sizes quickly at anchor using a genset.

Put some wood blocks under it to raise it up. That should let the bottom dry out and prevent a leak.
(assuming the leak is at the bottom)

We have a 6 gal and water is so hot that we have enough for a day for 2 people for shower, dishes etc but it is just enough for 2. As mine developed a leak too we are changing it for a 12 gal to get a bit more capacity.

L

Don't forget, this is, in effect, also an extension of your freshwater holding capacity - I would vote for bigger if you have room.

Bay Pelican has had a six gallon unit for now on 20 years. Have had four and five aboard. Never had a problem. Of course living at anchor we take short showers because of the value of fresh water, not hot water.

our isotherm unit stays warm from one day's running of the generator to the next.

You do have a built in small heat exchange on the engine to heat the water too?

I think I have about a 6 or 7 gal. hot water heater and have never run out. It have a very fast recovery. You might consider showering with a 'close friend' too.

20 sounds good. Depends on what your usage is. We had a 40 on the Hatt, no heat exchanger, never ran out even when using extravagantly when at the dock. As previously noted, gave us another 40 gallons of fresh water storage. We lived aboard full time, 2 adults, frequent guest via various other couples. We like taking long showers, and had both laundry washer and a full size household dishwasher. Based on our overall freshwater use when drawing from the tank, which I could measure very precisely via our Watercounter, I guesstimated that we could get by with a 20 or 30. there were times I considered adding yet another Watercounter (one of the best boat upgrades I ever did) to the heater's output to see how much hot water we used, but decided to spend it on diesel fuel instead.

just curious. With a 20 gallon unit, what is the size of the heater, 1,500 watts, 1,000, or 750 watts? And for a 110 volt system how long does it take running the generator to heat 20 gallons?

"no heat exchanger,"
Hmmm, my Lugger had a heat exchanger but I had to connect it.
My Cummins 380 has a heat exchanger that was hooked up by the builder. The only thing I can recommend is in and out quick throw valve be installed, "just in case".

Might want to check/confirmed with an engine tech.
IF you have an engine heat exchanger remember, the hot water produced will be "more hot" than just from the hot water tank. Might catch the guests off guard.
I have a red, engraved plaque glued to the inside of the shower, "Hot water is HOT".

OldDan1943 said:

...IF you have an engine heat exchanger remember, the hot water produced will be "more hot" than just from the hot water tank. Might catch the guests off guard.
I have a red, engraved plaque glued to the inside of the shower, "Hot water is HOT".

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You’re right, it can be a problem but for less than $100 you can add a mixing valve and don’t have to worry about the water heater water temp. I’m surprised they aren’t standard on new boat builds for the reason you mentioned.

Bay Pelican said:

just curious. With a 20 gallon unit, what is the size of the heater, 1,500 watts, 1,000, or 750 watts? And for a 110 volt system how long does it take running the generator to heat 20 gallons?

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I did the math for mine the othet day....it is dependent on temperature rise.


If heating from 60 degree water versus 90 degree water in the heater and what is going in...the time is quite significant..so your question cant be answered without a few givens..

I wandered down into my AT34 engine room and came up with the following about the hot water heater:
Seaward Model F-1200, 11 gallons, 120 volts.

I am making the assumption it is the standard hot water heater because if fits perfectly on the shelf.

Standard for your model vessel?

psneeld said:

Standard for your model vessel?

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Yes. Best guess based upon the 'fit'.

Thanks for all the feedback. The water heater is in a position that requires removing exhaust components from the port engine to get it out. Called the yard I regularly use and they sent a mechanic over. Took about 2 minutes to locate a leak from the fitting that is used to drain the tank. It's a faucet tap like fitting made of plastic and screwed into a brass female fitting on the tank. It was leaking from the threads. He removed the entire fitting and replaced it with a brass plug. All is fine now. Whew!

You just save the price of a new expensive water heater... CHAMPAGNE!!!

I have a 20 gallon Raritan with a tempering valve. Have never run out of hot water and can sit on the hook for a second night without running out. Nice to be able to sit for 36 hours without running the generator.

Ted

psneeld said:

I did the math for mine the othet day....it is dependent on temperature rise.


If heating from 60 degree water versus 90 degree water in the heater and what is going in...the time is quite significant..so your question cant be answered without a few givens..

Click to expand...

My question about the time to heat the water in a 20 gallon tank relates to the amount of time needed to run the generator when you are at anchor for several consecutive days. If you are on shore power, or if you are moving and use the main engine to heat water this is a non-issue. My question relates to a boat at anchor for extended periods. Thus the water is already on the boat. Assuming the water in the heater is 75 degrees to match a 70-80 degree outside temperature.

On Bay Pelican we had a 1500 watt, 6 gallon, 110v unit. Took 15 minutes to heat the water. We deliberately switched to a 750 watt element to reduce the draw on the generator when heating water. It now takes 30 minutes of run time.

To explain the draw on the generator when we start the generator (8 kw) we have two 135 amp chargers, the refrigerator, freezer and the water heater on, as well as normal household AC usage. With the 1500 watt unit the total initial draw would drop the generators output frequency (hertz) from 61 to 57 or 56. With the 750 watt unit the hertz drops to 59 or so. Using a 1,500 watt unit I reduced the draw by cutting back on the chargers until the water heater shut off (clear signal from my draw and hertz meters). We also avoided using appliances with significant draw, coffee pot, toaster etc.

If I project the time required for heating the water in a 12 gallon unit by just doubling the time of my six gallon unit it would be 30 minutes at 1500 watts or 60 minutes at 750 watts. Using the same projection the 20 gallon unit would be approximately 1 hour 40 minutes at 750 watts or 50 minutes at 1,500 watts.

Normal nightime generator run time on Bay Pelican is less than 45 minutes. It seems that a larger water heater at anchor would increase the run time. This factor may be important to some cruisers.

I agree....but cant say for sure that doubling the water volume would double the time.

There might be some losses, but with an immersed element, they may be insignificant.

Your times projections seem pretty good.

I did the math usung kW to Btu, and Btus needed to raise temp of water. Seemed for 8 gallons for a 60 degree rise.... well over an hour with my 750W element...

But I did a bunch of calculations and I forget now as they were rough and I figured I would pkay around with them next month while sunning in the Keys.... ..... and worrying less about thermal rise....

OldDan1943 said:

I wandered down into my AT34 engine room and came up with the following about the hot water heater:
Seaward Model F-1200, 11 gallons, 120 volts .

Click to expand...

My Seaward Al tank catastrophically crapped out after 9 years. The local yard advises unlined Al tanks require a watchful eye. It appeared the heat exchanger metals were not compatible with the tank. EMFs at work maybe?

Lou_tribal said:

You just save the price of a new expensive water heater... CHAMPAGNE!!!

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Interestingly, we would all spend the money on a hot water heater but never on a good bottle of champagne.