Point of Use Water Heaters

[Senojev]

A few bits of info first about our trawler usage. Never on shore power, about 80% anchored often for days at a time, located in 45 deg. N, 1600W solar, 700Ahr AGM (actual), 9kW genset, 15 gal hot water tank, all electric boat. We do not use the genset except when solar does not get us to 100% or very close or when we run a large water maker. Our heater is plumbed into engine system.

On a good solar day we can get to 100% SOC with no problem. On a very good day we can heat the water tank as well. The problem is the tank rarely gets fully used in the same day and by the next day is not warm enough for showers as it has partially filled with cold water.

I am considering adding a 1500W 3 gallon point of use heater (not a tankless heater) in the head plumbed into the hot water line. From my calculations, we could power that for 20 minutes twice daily for a relatively small consumption compared to the 15 gallon heater, getting two showers and not wasting water to get the hot water flowing in the shower.

Any experience out there with these types of heaters or comments for or against.

Thanks

 

[mvweebles]

Sounds like a workable plan. You have a lot of solar compared to battery capacity so powering 1500w heater makes sense.

I have 800w solar and 700ah LiFePO4 so a bit different dynamic. I went with an Isotemp water heater which is reportedly very well insulated, and a 750w heating element. I went from a 10g Raritan to a 6g Isotemp which has worked well for me in the warmer waters as I head south.

Peter

 

[O C Diver]

A few bits of info first about our trawler usage. Never on shore power, about 80% anchored often for days at a time, located in 45 deg. N, 1600W solar, 700Ahr AGM (actual), 9kW genset, 15 gal hot water tank, all electric boat. We do not use the genset except when solar does not get us to 100% or very close or when we run a large water maker. Our heater is plumbed into engine system.

On a good solar day we can get to 100% SOC with no problem. On a very good day we can heat the water tank as well. The problem is the tank rarely gets fully used in the same day and by the next day is not warm enough for showers as it has partially filled with cold water.

I am considering adding a 1500W 3 gallon point of use heater (not a tankless heater) in the head plumbed into the hot water line. From my calculations, we could power that for 20 minutes twice daily for a relatively small consumption compared to the 15 gallon heater, getting two showers and not wasting water to get the hot water flowing in the shower.

Any experience out there with these types of heaters or comments for or against.

Thanks

Before heading down that road, I would consider experimenting with how much generator time it takes to make the luke warm water useable. Might also consider adding external insulation to the water heater.

Ted

 

[Comodave]

We had a Seaward water heater in a previous boat that had the engine heat exchanger in it so the water was heated to 180. It would stay hot, not warm, for 2 days. Maybe a new water heater with good insulation?

 

[Simi 60]

We have a 25 litre Rheem 240v 2.4kw onboard
Never run out of hot and takes about 15 minutes to charge.
All runs off of lifepo4 and solar, stays on continuously.

Before that was 180 litre 240v 1.8kw power sucking p.o.s that we had to control manually, load share and should have got rid of 6 years prior.

 

[Mambo42]

My water heater is heated via electricity and the engine coolant. It only takes about 20 min to heat up the water on electricity and since the heater is 1000 W at 220 V, which means 45 Amps at 24 V, it only takes 15 Amps to heat the water, so we don't mind when we draw that from the batteries.
When the engines run they will heat the water and that means when you come into an anchorage you can comfortably take a shower after your day at sea.

One thing I do have to keep in mind is the following. When we take a shower in winter time we also have a heating element that warms up the shower area, but that element draws 1500 W @ at 220 V, in other words about 65 Amps at 24 V. Then of course the water pump has to switch on and that is another 65 Amps at 24 V. Lastly we have the water heater, which will also switch on when you take a shower and that is another 45 Amps. So taking a shower really draws 175 Amps from the batteries, which is quite a bit. If I then add the normal load of the boat I get to about 200 Amps total during a period of around 15 - 20 min.
So not only look at just the water heater, but also to any additional equipment and find on which fuse they are connected. If they would all be on the same fuse you could run into trouble. E.g. we used to have a 16 A (220V) shore power connection, but we now changed that to 32 Amps. Everytime we would take a shower the shore fuse would pop.

 

[Simi 60]

.

One thing I do have to keep in mind is the following. When we take a shower in winter time we also have a heating element that warms up the shower area, but that element draws 1500 W @ at 220 V, in other words about 65 Amps at 24 V. Then of course the water pump has to switch on and that is another 65 Amps at 24 V. Lastly we have the water heater, which will also switch on when you take a shower and that is another 45 Amps. So taking a shower really draws 175 Amps from the batteries, which is quite a bit. If I then add the normal load of the boat I get to about 200 Amps total during a period of around 15 - 20 min.

WTF
65 amps for a water pump?

 

[Mambo42]

WTF
65 amps for a water pump?

Yep, it is a hydrofoor, uses 1500 W at 220 V which is about 65 amps at 24 V. Can't help it, it was already in the boat, don't see the need to exchange it. At least I have very good water pressure in the whole boat.

 

[luna]

Adding insulation or replacing a perfectly serviceable hot water tank with one with "good insulation" will not solve this issue as the problem appears to be (like us) the feed water to the original hot water tank is cold, likely 50 degrees F, not 85 F. like Florida.

If the original tank is holding luke warm water at say 85 F. you will likely get your 2 quick showers 20 minutes apart with the new POU tank hot. The 2nd shower will be cooler at the end as the lukewarm water is now cooler.

I have 2 POU, 3 Gal. tanks, one supplies only the galley sink. The logic here is that when the boat is at it's home port for days, this gives me enough hot water to wash the lunch dishes, my hands and maybe clean whatever I'm working on, then I go home. The feed water is cold because it's sourced from the 20 Gal. water heater that is not energized.

The 2nd one is plumbed in right at the outlet of the 20 Gal. water heater and will get you a small amount of hot water to all taps on board. This also means that the galley sink can get about double the hot water if both POU tanks are energized.

Both work quite well, With 1.5 kW elements and 50 F. feed water, about 20 minutes to 150 F.

I also installed a loop and circ. pump so that while underway the 2nd POU water heater can, by way of the alternator and inverter, heat the 20 Gal. hot water tank. It' nice to arrive at your anchorage for the night with full batteries and lots of hot water without running the genset.

You logic is sound, but by day 2 you will have to increase the temperature of the water in the original hot water tank unless you can tolerate a cold ending to your showers.

I don' t have solar yet, nor engine coolant sourced heat, never.

 

[Jeff F]

I am considering adding a 1500W 3 gallon point of use heater (not a tankless heater) in the head plumbed into the hot water line. From my calculations, we could power that for 20 minutes twice daily for a relatively small consumption compared to the 15 gallon heater, getting two showers and not wasting water to get the hot water flowing in the shower.

Makes sense to me. I have a diesel furnace that provides hot water, but it bugs me to have to run the shower for a while to get the hot water through the lines.

What about HW at the galley?

 

[dvarholy]

I have three ways to heat the water in my 12 gallon Raritan. One, run the starboard engine for 20 minutes. Two, shore power or generator for about 30 minutes. Three, run the galley WSHP for about an hour on a warm day. Yes, I am an HVAC tech and use a heat exchanger from an old drinking fountain to recover waste heat from one of my WSHPs. Living aboard full time and my water heater's circuit breaker has been off since May. A small "solar" pump is used to circulate the water and is controlled by a pressure switch. Another pressure switch controls the seawater cooling pump, which only has to run after the water heater warms up. From October to April, I must use the electric element. I installed a lower wattage element, 1kW, to reduce my peak load in the winter.

Daniel

 

[Lepke]

I have a 50 gallon house water heater. It's surrounded by 2" foam, top, bottom, and sides. Also the water lines are insulated including cold so it doesn't draw heat from the tank. On the boat alone, I have hot water for 3 days including showers. Insulation helps a lot.

 

[motion30]

I have a 3 gallon whale heater. I makes enough hot water to take a shower in 5 minutes. Draw is high at around 147 amps dc tru the inverter.

 

[SteveK]

Makes sense to me. I have a diesel furnace that provides hot water, but it bugs me to have to run the shower for a while to get the hot water through the lines.

What about HW at the galley?

I have a plan on the back burner, near the bottom of the To DO list of priorities. My two heads, sink & shower have one hot water feed line daisy chained. I will be teeing into the end of the run and back into the inlet of the circ pump. In theory if this circuit is opened the domestic water pump will circulate the water bringing hot to the sinks and showers before it goes down the drain.
Then do similar to galley sink.