240VAC water heater wiring?

[Mischief Managed]

When replacing a water heater, I recommend using extra long silicone heater hose and brass 3/4" MHT/FHT connectors (like washing machine hoses). Makes Winterizing a breeze, and when the water heater needs to be replaced in the future, the long and flexible hoses allow for all styles of water heaters to be installed without re-configuring the plumbing beyond moving some hoses around.

 

[luna]

The Isotherm Catalog for USA on page 78 of 84 lists all of the horizontal Basic units as 16" in diameter, weight in pounds, volume in gallons, you know real units.

Here is the link. https://www.indelwebastomarine.com/....com/EN_US/Documents/Isotherm-Catalog-USA.pdf

Hopefully it's a hot link, otherwise copy and paste it into your browser.

Note that the only wattage listed is 750, albeit in 2 voltages. The notes further say some models can accept 1200 or 2000 W elements.

Perhaps you have been using the International Catalog which is expressed using Metric units.

Unless Isotherm uses some proprietary design of element, higher wattage elements are likely available cheaply at your local HD, but use an Inconel based element for longevity.

To deliver 3kW from 240V split phase power only requires 12.5 amps per leg, but due to the loads duration, prudent design would require at least 12ga wire and a 20 Amp 2 pole breaker. But be sure to do your own research, I'm just some guy on a forum.

 

[rslifkin]

If your 11 Gal. water heater has a 1200 W element and you don't consider passive gains or losses during the heating period then it will take about 2 hours to raise the water temperature 90º F.

Using a 750 W element the time goes to over 3.25 hours.

Using the 20 Gal tank and the 750 W element you are now are at about 6 hours to make temp.

I don't know about your use patterns but if my boat is in the house unused for a few days the water heater is not energized.
I would not consider it acceptable to have to be at the dock for more than at most a couple of hours for the water to heat. I always leave with a full tank of hot water and by choice do not heat water using waste heat from the engines.

Further, we often have 6 or so people overnight and the recovery time using a 3 kW element speeds the morning shower process, regardless as to whether we are on the dock plugged in or on the hook.

Recovery time for us is important.

We leave the water heater on full time any time we're on shore power even if we're not on the boat, so heating time is only an issue when we're away from shore power and heating with the generator (only 2 of us on board, so we don't deplete the heater when showering). But with good insulation, the water heater is typically still warm enough that it gets back up to temp in an hour or less with the 1200W element with 1 heating cycle per day (the Isotemp heater heats to 167* and uses a mixing valve to provide hot water at a more reasonable temp). 45 - 60 minutes is about how long we'd need the generator for other non-inverter activities like cooking dinner anyway.

Long term, when I make sufficient upgrades to heat water on battery/solar power, I'll swap the smaller 750W element in as the low power draw will be preferable to faster heating in that use case. With lots of people on board, fast recovery becomes more important.

I agree probably not frequency sensitive, but I think too much trouble to change the whole electrical system given the Torrid 240VAC version would be a straightforward connection mirroring our original. (And I haven't a clue how to get 3-wire 230VAC from a 4-wire 240VAC system.)

That part is easy, you just don't use the neutral wire. So in place of L and N marked for a European setup (where you get 230V from L, N, and Ground) the US setup has L1, L2, N, and Ground. L1 - L2 gives 240V, so you'd use L1 and L2 to the heater. L1 or L2 to N gives 120V, so you don't need the neutral connection if you're only using 240V.

 

[psneeld]

Isotherm I believe uses a proprietary element... never seen one anyplace else....picture below.

I used engine waste heat to heat the water heater...seemed silly not to. As long as the hoses were easy to check maintenance wise...never a problem with several boats and 10 years living aboard. The engine waste heat warmed the 11 gallons water in less than an hour, maybe not to highest temp, but useful for showering and washing dishes.

 

[rslifkin]

Isotherm I believe uses a proprietary element... never seen one anyplace else....

I used engine waste heat to heat the water heater...seemed silly not to. As long as the hoses were easy to check maintenance wise...never a problem with several boats.

Agreed, I think they are proprietary. Not particularly expensive or hard to change though. I bought my heater with the standard 750W element and then bought the 1200W element to swap in. That ended up being easier than special ordering one with the 1200W element pre-installed.

 

[ranger58sb]

The Isotherm Catalog for USA on page 78 of 84 lists all of the horizontal Basic units as 16" in diameter, weight in pounds, volume in gallons, you know real units.

Here is the link. https://www.indelwebastomarine.com/....com/EN_US/Documents/Isotherm-Catalog-USA.pdf

Hopefully it's a hot link, otherwise copy and paste it into your browser.

To deliver 3kW from 240V split phase power only requires 12.5 amps per leg, but due to the loads duration, prudent design would require at least 12ga wire and a 20 Amp 2 pole breaker. But be sure to do your own research, I'm just some guy on a forum.

Interesting. I only looked here:
https://www.indelwebastomarine.com/us/isotemp/

And here:
https://www.indelwebastomarine.com/us/products/basic-slim-water-heaters/

Not exactly the same info as in the catalog link. And the 20G version in the catalog with 16" diameter is also 42" long, which exceeds my platform length. But not to worry...

Yeah, I'd have said the 12.5A is too close to our probable 15A breaker size, and also I haven't checked the existing wiring size yet. But given that our original is a 240V/1500W element, I'd expect breaker and wire size is all optimized for that... and I don't have much appetite for changing breaker or wire sizes... especially since our original 240V/1500W system has been entirely adequate.

That part is easy, you just don't use the neutral wire. So in place of L and N marked for a European setup (where you get 230V from L, N, and Ground) the US setup has L1, L2, N, and Ground. L1 - L2 gives 240V, so you'd use L1 and L2 to the heater. L1 or L2 to N gives 120V, so you don't need the neutral connection if you're only using 240V.

Hmmm... the 240V version doesn't use the neutral wire already. But I suspect there's also a significant difference in likely wire gauges between a 3-wire and a 4-wire set-up? Pulling new wire would be approximately the next to last thing I'd want to do.

I'm new to 240VAC 4-wire stuff, so sometimes I don't understand the magic involved... and I haven't come to terms yet with the differences between that and 230VAC 3-wire...

So far, though, it still seems to be coming down to a potentially easy solution: horizontal Torrid 17 240VAC, with the only pain being some higher cost. Assuming my eyeball guesstimate about getting it into place without removing engine parts is close to correct.

Well, I'll probably have to fiddle with existing water and vent line lengths versus new hook-up locations, too... but that looks like it'd be the case with all the other brands/models except for the Kuuma. And if I have to remove the Atwood with a Sawz-All (maybe figurativly) a new Kuuma clone isn't much of an attraction either.

-Chris