120 volt AC Tankless Electric Water Heater

[sailscubasurf]

I am considering putting in a 102 volt ac tankless electric water heater at my galley sink and would like to get any recommendations / advice for fellow members if they have installed one.

What brand(s) do you suggest?
What is the minimum GPH I should look for?
Is the temperature rise sufficient?

Gary

[john61ct]

Tankless means you need to run the genny to get hot water when you're away from shore power?

Maybe look at 12V or propane, or a well-insulated tank setup if you run the genny daily.

[Chuck34]

Tankless water heaters are great if you have gas.
Electric...not so good. You need a lot of amps. On a boat, I can see one having to turn off other electricity hogs just to turn on the hot water spigot, otherwise, you going to be popping breakers every time you use hot water.

Better off with a tank model.

[sailorchic34]

it is amazing how many kw is needed to heat water instantly. For example a small 3.5 kw 120v unit will heat 1/2 gpm, roughly 47 degrees. So if you have 50 degree cold water, it will heat it to 97 degrees which will seem luke warm. Doing so will use 29 amps or all of a 30 amp shore power cable.

A 1/2 gpm is barely enough for hand washing. Most galley faucets will flow 1.5 gpm. If I was using this type for hand washing I would be specifying at least a 6kw unit (which is 240v/208v). For galley, you would need at least a 9kw unit, which is too large a load for shore power.

[john61ct]

But propane instant works great, can really be conservative but of course depends on users being aware it is a finite resource.

Nice thing about a dual-element well-insulated tank setup is the 12V side makes a great load dump for free "excess" solar production if the bank gets to 90%+ and acceptance is falling quite low in the middle of the day.

[sailscubasurf]

Ok, your replies have convinced me not to go with an electric tankless.

So in everyone's experience, what is the best propane Tankless/ventless water heater?

[Chuck34]

Unless you already have propane installed on your boat or you want to put propane on your boat for cooking, heating....
Keep it simple and just install a small water heater. Takes up less space, no need for a dedicated propane locker, doesn't use gobs of electricity....just much simpler.

[john61ct]

Meaning a well-insulated tank version.

Dual elements so either mains/genny or solar/battery can be used.

I agree adding propane infrastructure just for a HWS may be overkill.

Lowering your energy requirements is the "investment" with the highest and fastest return.

[foufou]

1/2 gallons per minutes seems extravagant for hand washing in my opinion. Water use extravagance is a modern flaw. Your mileage may vary

[Brewgyver]

Actually, 0.5 GPM is the water conservation spec for hand sinks. Put another way, it takes almost 8 seconds to pour a cup of water. The best way to use even less water for hand washing is with a hands-free faucet, allowing efficient washing with just a couple of short run times to wet, lather and rinse. Battery operated units work fine on boats as well as ashore. Wash your hands with mere ounces of water.

[denverd0n]

Have to wonder why you are so set on a tankless system. Gas tankless systems work pretty well, but none of them (at least, that I'm aware of) are rated for marine use. It's not absolutely necessary to have one rated for marine use, but you'd better be sure that you have a really, really knowledgeable installer put it in. Because if you have any problems later, expect your insurance company to give you grief over the non-certified installation.

Tank systems have been around on boats for decades. True, they are not the most efficient, but they work, they're relatively inexpensive, and they are an accepted and well known commodity.

Just wondering if you have some specific reason that you don't want to consider a standard tank installation.

[Paul L]

On-demand, tankless marine diesel hot water systems are available in boat heaters built by ITR (Hurricane Zephyer)

[transmitterdan]

Any tankless system needs a huge amount of energy to instantly heat water. To take 1/2 gallon from 20C to 50C in 6 seconds requires over 35 kilowatts of power. For a 120V system that is about 300A of current. For a gas or diesel system it requires even more energy per minute because of heat losses. Basically these things are not that practical on a small-medium boat.

[Paul L]

Originally Posted by transmitterdan

Any tankless system needs a huge amount of energy to instantly heat water. To take 1/2 gallon from 20C to 50C in 6 seconds requires over 35 kilowatts of power. For a 120V system that is about 300A of current. For a gas or diesel system it requires even more energy per minute because of heat losses. Basically these things are not that practical on a small-medium boat.

So how much diesel do you think you need to burn for a 10 min shower? It is miniscule with our ITR.

[GordMay]

Low flow rate instant water heaters will only work with very low wattage heating elements.
For an excellent explanation, see Gary Klein’s Reply 3 ➥ Tankless water heater with a low minimum flow rate? | GreenBuildingAdvisor.com