What size water heater?

[Tom.B]

Hello team!

I am considering downsizing our water heater. Currently we have a 20g Raritan that is 22 years old. It’s just a matter of time before it fails. Anyway, it lives on the outboard side of the starboard motor and makes for some cramped quarters doing regular maintenance on things like the impeller and heat exchanger (just to name a couple). It is just the two of us… we never really have guests onboard and don’t have kids or grandkids. We rarely shower within and hour or two (or day or two) of each other, so it has a long time to recover. Even then, we are in the habit of not letting the water run the whole time anyway. So, would an 8 gallon heater be enough? It sure would open up a ton of space and at only 750w, we could conceivably run it off the inverter for a short time if we needed to.

What say ye’?

Thanks!

 

[SteveK]

Here is the one on my back burner for an upgrade.
https://www.pysystems.ca/resources/...em-provides-heat-and-hot-water-for-your-boat/

 

[rslifkin]

I just swapped out my 12 gallon Raritan for an 11 gallon Isotemp. The Raritan was big enough and so far the Isotemp has been great. It's definitely better insulated and the mixing valve on the output is nice. I did upgrade to the optional 1200w heating element (Raritan was 1250w) for faster heating on generator power compared to the standard 750w.

 

[DennisB1]

If you install a mixing valve to control temperature to 120 F a smaller tank temp can be raised to a higher temperature effectively increasing the supply of hot water. This helps in down sizing the tank.

 

[tiltrider1]

Size is one thing and water temp is another. Since you rarely have guest and never children you could consider a 6 gallon heater that is set to 180 degrees. There are some dangers such as never flush when some one is in the shower. You might find you have the same amount of usable hot water as a 20 gallon set at 120 degrees.

I have a 30 gallon set at 160 degrees. I use a mixing valve after the hot water tank to bring it down to 130 degrees. You can shower for an hour and not run out of hot water.

 

[Comodave]

A 10 or 11 gallon will work fine for 2 people. Especially if it has a mixing valve and you set the temp up high in the water heater. I don’t think I would go with a 6 gallon.

 

[O C Diver]

As long as YOU shower first, size doesn't matter.

I second the tempering valve. Installed one on my Raritan and have been very happy with it.

Regarding size, it depends on where you boat. Many boats have their water tanks close to the hull. The water in the tanks comes close to the outside water temperature. That's fine in Florida. In colder climates you tend to use more hot water to temper the cold. Also, after showering does that mean there's no warm / tepid water for the better half to wash her face with in the morning?

Ted

 

[Simi 60]

Full time cruiser friends on two other vessels have 25 litre - 6.6 gal dux 240v household units and reckon they are sufficient and, only take 20 minutes to get to temp..

Will be getting one ourselves to replace the 140 litre - 36 gal Rheem we currently have that sucks around 80amps @ 24v for an hour and a half.
Massive waste of power considering we only use hot water for washing up and hardly any in the shower.

$400 at big hardware stores

 

[healhustler]

I replaced my old original iron 5 gal. water heater a couple of years ago with a 6 gallon Isotemp. Starting with a Florida tank temperature of 79-80 degrees, after a 20 minute 110V heat, the system is able to deliver full blast, good pressure, four minutes of 1.5 GPM at 95 degrees, (a warm shower) before cooling back down to tank temperature. This is with no mixing with cold water at the faucet, hot side only. For our use, this is an easy, relaxing shower for each of us.

With a 40 minute heat, the system is able to provide 5 minutes and 30 seconds of hot shower water beginning at 108 degrees and still at 100 degrees at the 5:30 mark, this using about 3/4 hot to 1/4 cold at the mixer.

After a 1 hour heat, the system will deliver 8 minutes of hot shower water at 1/2 of hot & cold mixing at the faucet. This provides my wife and I with a hot shower each after the heat, and even though we are unplugged, also a warm shower for each of us the next morning.
Temperature of the Isotemp water heater is set at 160 degrees.

All the above is with plug-in only heating…no engine hookup.

 

[OldDan1943]

When folks talk a mixing valve, I am not sure what they are talking about.
I have 11 gal Seaward Model F1200 hot water heater. Also I have the engine heat exchanger piped to water heater tank.
I have ‘supported’ 4 people and still had hot water left.

 

[Tom.B]

I’m not sure I fully understand the “mixing” system or “mixing valve” thing. Can someone explain it, please?

-edit-
Nevermind… it was right there in the product description. Doh!

All Isotemp water heaters come standard with a mixing valve
Every Isotemp tank features a safety mixing valve that regulates the temperature of the water coming out of the tank so that water heated to 160+ degrees will not scald boat owners or their guests
Temperature of the hot water coming out of the tank can be adjusted to the preference of the owner by turning the mixing valve on the water heater
This feature allows the thermostat to be set at a higher temperature, while keeping the user safe from scalding
It also extends the capacity of onboard hot water by using only a fraction of the water in the tank to produce the desired water temperature

 

[Simi 60]

I’m not sure I fully understand the “mixing” system or “mixing valve” thing. Can someone explain it, please?

Safety device to prevent scalding

https://www.sydneyplumbinghotwater.com.au/hot-water-tempering-valve/

 

[psneeld]

Isotemp 8 gallon, has a tempering valve and was perfect for my 40 footer, with 2 liveaboards. Never ran out of hot water, heated fast even with 750W and didnt tax electrics, stayex hot for a day, warm for 48 hrs depending if no electric.

 

[Comodave]

A mixing valve takes some cold water and mixes it with the hot water to bring it down to a safe temperature, not scalding. It will also extend the useful amount of hot water since it adds some cold to it. You can do the same thing at the faucet but you have the possibility of scalding someone.

 

[koliver]

Hello team!

I am considering downsizing our water heater. Currently we have a 20g Raritan that is 22 years old. It’s just a matter of time before it fails.

What say ye’?

Thanks!

How do you measure the amount of time left in its life? Like people, every item on your boat is going to die, you just don't know when. Does your water heater have cancer? Is there some family history of fatal illness?
I will replace mine when it fails. It is a Torrid. I think 18 gal, but I don't know for sure. It sits in a handy place, simple to get at and replace when the time comes. Hopefully it is not on the slippery slope heading towards failure, as it is not displaying any symptoms of any fatal illness.
I have a daughter its age, at 42.

 

[rslifkin]

How do you measure the amount of time left in its life? Like people, every item on your boat is going to die, you just don't know when. Does your water heater have cancer? Is there some family history of fatal illness?
I will replace mine when it fails. It is a Torrid. I think 18 gal, but I don't know for sure. It sits in a handy place, simple to get at and replace when the time comes. Hopefully it is not on the slippery slope heading towards failure, as it is not displaying any symptoms of any fatal illness.
I have a daughter its age, at 42.

Depends on how well you can assess condition. The Raritan heaters are a lined steel tank. So if it's showing significant rust under the insulation, it may be near the end. The one I replaced was 17 years old and still working, but it was rusty and I wanted a better insulated unit. When I dumped the last bit of water out, I got some rusty sludge. So I'm thinking the interior lining was failing and it was probably near end of life.

 

[Tom.B]

Depends on how well you can assess condition. The Raritan heaters are a lined steel tank. So if it's showing significant rust under the insulation, it may be near the end. The one I replaced was 17 years old and still working, but it was rusty and I wanted a better unit. When I dumped the last bit of water out, I got some rusty sludge. So I'm thinking the interior lining was failing and it was probably near end of life.

This… and I have done zero routine maintenance to it. Yes, that’s on me, but waiting only means that it will fail at some inopportune time AND won’t add any additional room for engine maintenance until I do. I may flush it out and see what happens. That’s free, but I still think it should be done so it doesn’t fail at the worst time.

 

[DDW]

It depends on what you expect from a shower. I removed the 11 gallon Raritan and replaced it with a 20L Isotemp (that's 5.3 gallons in old money) and the two of us can take a shower without waiting between. We don't waste water, but don't leave the shower dirty or soapy either. It does have a mixing valve (more properly called a tempering valve).

 

[RedRascal]

I've had good luck getting two "boat showers" out of a 6 gallon tank. First shower can have very hot water and the second gets comfortable shower water but not super hot. I would think an 8 or 9 gallon tank should match your needs.

 

[Oeanda]

Our Seaward heater with six gallon tank easily provides enough for one person to shower with. The allotment can be stretched out and rationed in various fairly obvious ways. It also helps if your shower space is comfortable and warm, rather than below freezing, etc.

Of course there’s the paradox where -if the space is uncomfortable and freezing cold there’s the urge to GTFO sooner, balanced by the urge to stay under the hot water as long as possible. Compared to -having it warm and comfy where you aren’t in such a hurry so tend to linger, but also have the luxury of not getting frostbite if you ration by turning off the water for a minute while soaping up.

Not sure what the mathematical equation is for all that.

Anyway, never once has our second in line needed hot water sooner than the time it took for them to find the round tuit.
It’s always been surprisingly adequate. Including for dishes etc. and when it isn’t, just wait a little while. We are pretty thrifty with the hot water, but then I assume most boaters are.

 

[Tom.B]

Thanks everyone. This is helpful.

It is a bit scary jumping from a 20g down to an 8g. That’s a long way. I think we’ll be fine though. Bess is a little concerned that it would affect resale, but I am thinking that a new water heater would score more points than old and nobody, including me, knows what size anyone needs. It would be interesting to put an inline flow gauge on the hot side to really get an idea of what we use during a typical shower.

 

[mvweebles]

In my opinion, zero effect on resale to go smaller.

I went from an old 12g Raritan (I think it was 12g - round fiberglass I bought 20 years ago) to a 6g isotemp. Two reasons. I was in cooler San Francisco when I bought and installed the old Raritan and I will be in Florida. Second reason was I moved it out of the engine room into the lazarette to gain better engine access. I also went with the 750w heating element to better run off solar at anchor; and have less contention when plugged in (I have a 30 amp boat)

Good luck.

Peter

 

[psneeld]

Frame of reference can be important.

Shorter term cruisers may always think of conserving water in general, let alone hot water.

Liveaboards may think more broadly if hooked to city water and unlimited electricity.

I have found the cheapo 6 gallon water heaters to be a bit shy if showers are taken randomly throughout the day and hot water might have been used for various tasks throughout the day.

When I replaced, the few extra inches spared to go up to 8 gallons and dollars on a better water heater was one of the best upgrades I did. If I had the room, sure going up a few more gallons wouldn't hurt if on a liveaboard or cruise a lot.

Funny how some Wil, spend $1000 dollars on a larger, fancier chartplotter that the rarely really need but not a few hundred extra on something used most every say aboard.

 

[rslifkin]

My logic in not going smaller than the 11 gallon was not so much the amount of hot water we need, but how long it'll stay hot without power to the heater. I figured the larger tank should have less surface area per gallon of water contained, so it'll stay hot longer when away from shore power (my tank isn't plumbed for engine heat and we rarely run the generator more than once a day).



That same criteria pushed me to the Isotemp, as it has the best insulation from what I can find (and the shape is easy to add more insulation if desired). I also insulated all of the connections to the unit, etc. to minimize heat loss.

 

[Bmarler]

my last boat had a 35 gallon. never ran out on that one. (liveaboard use) our new liveaboard has a ten gallon. there's also an insta-hot sort of thing in line to the shower stall. i reckon we could shower pretty much continuously till the tank was empty.

 

[O C Diver]

My boat came with a 20 gallon Raritan. It was 13 years old when I started my refit. With the engine, generator, and floor out of the boat, it was never going to be easier to replace it. I figured that if I do it then, it would outlive my ownership of the boat. Ended up putting the same unit back. As I travel solo most of the time, unless I'm way up north, there's enough hot water for a second day if I don't move the boat. Other than cost, there was no advantage to a smaller unit. On the occasions when there have been 3 of us on the boat, it's nice to know you're not going to run out of hot water. Also, when I'm up north and the water in the tanks is cold, it's really nice to be able to do the dishes in warm water and not wonder if there will be enough left at shower time.

Ted

 

[mvweebles]

Bigger water heater is nice, and as rslifkin notes, offers heat retention. On a 36 footer with 500g of diesel tankage, space is a premium. I am constantly making compromises. Getting the 12g water heater out of the engine room and replacing with a higher quality 6g tucked away was an easy choice to make. We've never had issues with rationing hot water but I have to confess, our onboard lifestyle somewhat emulates classic sailboat cruisers circa 1970s. Oddly I suppose, we find comfort in a more minimalist approach to boating. Not sure that's common even amongst sailors these days. For the first 15 years, our Willard 36 was used primarily as a day-boat with plenty of friends, and short vacation cruises of up to a couple weeks. Now, it is setup for the two of us for long-term live aboard. We have room for a second couple as long as they are more backpacker types vs Marriott types.

Peter

 

[OldDan1943]

Remember, one can replace the electrical heating elements. Of course one should investigate the sludge level in the tank prior to making a decision.

 

[OldDan1943]

If you are starting with a originally equipped boat, the electrical systems are generally designed for the generators capacity while understanding there may be some electrical load shifting.
I would suggesting 2 options.
1. Replace with identical capacity equipment
2. Replace with a less demanding piece of equipment.

IMO, don’t go larger. You might unbalance the demands or ability of, for example, the generator.

 

[Simi 60]

.

When I replaced, the few extra inches spared to go up to 8 gallons and dollars on a better water heater was one of the best upgrades I did. If I had the room, sure going up a few more gallons wouldn't hurt if on a liveaboard or cruise a lot.

It "hurts" if power generation is borderline.

A bigger than needed HWS ( we have 37 gallons) requires more power to keep it hot and, if you miss a heating cycle it takes even more power / longer time to get it back to temp

We very rarely used the Genset for our first 5 years out here, the 2.5kw of solar could do the HWS in the middle of the day and the batts would still be at 100% by day's end.

Now we have the big lifepo4 bank that can handle big load without voltage sag we run an electric kettle , an induction cooktop and a piemaker as extras.
Every 3rd day we make water, all off of battery.

Solar no longer keeps up and Genset is coming into play.
But if we get rid of the 10+ year old 37 gallon has that takes 1.5 hours to "top up"
And replace with 10 gallon or smaller that takes 20 minutes to top up I reckon we'll be back to excess solar production at days end