tankless water heaters

[Paul45c]

I'm going to need to replace my 15gal HW heater soon, and I'm looking covetously at the space that big boy takes up (outboard of the port engine). It sure would be nice to go with one of the new tankless types, but I've heard they use more power when they're running than does a conventional heater and I'm worried about blowing my main breaker when too much stuff is running.

I'm wondering if anyone knows specifics on current draw as a comparison with the old tank-style heater.

Assuming higher current draw on the tankless, I suppose I could just force the crew to be more disciplined with what is allowed to run at the same time. The only time I ever use hw, it seems, is for crew showers at the end of a cruising day; unfortunately, this is also when the admiral is cooking and at least the salon a/c is running because of that hot engine room right below it. Pop goes the breaker.

 

[SKYCHENEY]

We once had a boat with an electric water heater that also had a heat exchanger off of the engine. It was nice to have hot water without running the gennerator. I don't think I would want one of those tankless, though. It seems it would cause problems with amp draw and you may also not get enough hot water for 2 showers at a time.

 

[egaito]

I studied these for my home when we built it, and thought about it for the boat too. That 6 gallon tank gets used real fast in the winter when it's mixing with cold water.

You mentioned the draw, which is the big problem with these heaters for a boat, but there is another factor to consider, assuming you get past the draw. They only heat water a certain number of degrees over the input temperature, even when they're getting all the power they want. You have to look at the flow rating, and the temperature rise. If they aren't sufficient, you'll end up with the faucette on pure "hot" to get a good shower, and drawing everything your dock (or genset) and boat are worth to do it. Additionally, you end up with less overall water flow to the fixture as you're not mixing the cold circuit to get the desired temp.

If we could generate the power these things need (wonder if there's a diesel fired unit out there), they would be pretty cool on a boat. There are times I'd kill for a long hot shower...like after a day of dealing with a leaky holding tank!

 

[SKYCHENEY]

If you want a diesel fired unit, get a Wabasto. The are mainly used to preheat truck engines and cabs, but are also used in the RV industry to provide hot water heat and domestic hot water. Neat units. I put one in a coach that we converted and just rigged some relays to control zones.

 

[Paul45c]

Cool idea on the diesel, you guys. I was just thinking the same after browsing the tankless...many of the larger capacity units are natural gas-fired, so diesel also seemed a natural.

Yeah, it appears the lightest you can get away with on the tankless I've browsed thus far is 240v/50a. That's a lot! And yes, those are very restrictive as far as flow & how much temp they'll heat. At least where I am input temps are no prob -- high 60's would be the the lowest I'd typically reach. So, the unit would need to be able to heat a steady flow of about 60 degrees to do it right. Sounds like one other drawback for a tankless on a boat -- the water coming through the unit is what "wakes it up," so you'll have to run the tap until it comes online enough to heat. That'll waste water, though they say there are pumps that can reduce the wastage somehow. Sounds like a "forget it" for now.

At least one of the sites I browsed also carried a line of small conventional heaters and one of those looks like a winner -- a 15 gal Rheem that had a synthetic tank. That's the prob with my existing steel one -- it works fine, but it's got bad rust all around the bottom rim. Assuming the synthetic tank is fine sitting inches away from a 175 degree engine, that sounds like the way to go. I guess now my only question is on how big to go for a tank, since I've only got one galley sink, one head sink and a shower that can possibly use h/w. I rarely ever use h/w in the galley, and the same goes for the head sink. So, I'm not sure exactly how big a tank I'd need for just mainly shower usage. Again, I'm trying to save whatever space I can in the ER.

 

[yachtsmanbill]

Ive got a 12 gallon RHEEM 110vac (MAYBE 10amps cold) heater and it takes 2 non conserving showers to deplete it. Recovery is maybe 1/2 hour.
Water saver shower heads do help too. Elements usually last 5 years and are 10 ROYS at the HOMO DEPOT. ws

 

[Angela]

We have one of those tankless heaters in my office. Hate it! It's constantly requiring a reset of the breaker, but more importantly, and more consistently, it scalds folks. We can never find a happy medium of warm no matter how tediously we play with the faucet. It's either on enough to scald skin, or completely off. There is no middle ground with it. We have it for the purposes of having a dishwasher and it does fine for that. But, I'd NEVER want to take my chances and shower with it.

 

[Maynard Rupp]

We have one of those tankless heaters in my office. Hate it! It's constantly requiring a reset of the breaker, but more importantly, and more consistently, it scalds folks. We can never find a happy medium of warm no matter how tediously we play with the faucet. It's either on enough to scald skin, or completely off. There is no middle ground with it. We have it for the purposes of having a dishwasher and it does fine for that. But, I'd NEVER want to take my chances and shower with it.

And certainly not in your office, eh Angella?

 

[Boss Lady]

The flow rate is critical to get acceptable temperature control, these things are power hogs too. The flow rate is too low for a decent shower, and forget shampooing long hair and a good rinse if you put one of these in. We do not have enough amps on our boats for a real good tankless heater. The propane/natural gas ones work great, but look at the btu's available.

I just bought an all stainless 20 gallon water heater with built in heat exchanger for using engine heat to heat the water. The old one had a heat exchanger too. We always started taking showers on the way back to the dock if it wasn't too rough, and never ran out of hot water if the engines were running. The old one was a 12 gallon and the new one is 20, I am a water abuser when it comes to hot showers, so that explains the bigger tank, no navy showers here! Underway is no problem but on shorepower it takes time for the tank to heat back up after a couple of showers. The extra gallons are needed.

 

[shvldis]

Installed a tankless on our 58 when original water heater went bad. I spent the day removing the old, rewiring, pluming and installing new unit. Spent the next day replacing it with another tank type, they draw to much power and dont produce a great enough temp rise except at very low flow rate.

 

[spartonboat1]

Installed a tankless on our 58 when original water heater went bad. I spent the day removing the old, rewiring, pluming and installing new unit. Spent the next day replacing it with another tank type, they draw to much power and dont produce a great enough temp rise except at very low flow rate.

...nuff said!

 

[REBrueckner]

A Webasto or Hurricane diesel water heater will heat water quickly, but these are not made for tankless applications. However, since you are in Flordia and may not need much space heat aboard, a diesel fired heater is really overkill from a cost perspective. And they take about the space of an 8 or 10 gallon tank plus exhaust space.

It's hard to beat a standard electric water heater with a heat exchanger coil to permit "free" water heat from a main engine if you run you main engines much. If you sit in place for four,five days or longer, "free" engine heat is not much of a factor. A smaller tank, say ten gallons, will heat quickly while a larger tank, say 15 or 20 gallons, will take longer to heat but will stay hot longer.
A good potential alternative, depending on how you use your boat, is to run the water tank coil from your genny coolant...use "free" heat from it if you use it frequently. This means you are getting hot water with no electric power consumption, or can use both electric and the coolant together. Or you can heat the water tank from a main engine and run a heat exchanger from your genny cooling system...This may require a small circulation pump to pass water thru the water tank coil and secondary of the heat exchanger.

Also, relocating you water tank is another possibility as the length of hoses to and from an engine makes little difference. A valve on each line near the engine is a good idea just in case a leak develops in the water heater or connection hose.

Finally, instant hot water heaters are also available in propane.

 

[Paul45c]

As usual, good advice all. Thanks for the help.

 

[waymaker]

As usual, good advice all. Thanks for the help.

Paul,
What water heater did you decide to go with?
Are you happy with it?

 

[Paul45c]

I haven't made the swap yet, unfortunately. It's still on the list, but I'm leaning towards a simple replacement of similar type. The only thing I'm coin-flipping about now is the size. That 15 gal. may be overkill for a boat with only one head.

 

[thoward]

We had a 6 gal stainless in the 43' and I really liked it. You could cruise without the generator and still have hot water for 48 hours(that was in Fla winter)if you took short showers. The water thermostat was set really hot though.

 

[(Nobody You Know)]

I just bought an all stainless 20 gallon water heater with built in heat exchanger for using engine heat to heat the water.

Chris,

if I know you (and Starman) you are probably very diligent in installing HD water hoses and double clamps on that thing. It's just "one more link in a chain" where you can't afford failure. I guess others need to know this.

I heated water off an engine on 2 other boats without a problem (except on the Carver - ok so I screwed up once - where the mfg. installed the wrong fitting on the water tank and made up for it with a glob of teflon tape. No engine trouble, just a hard-to-get-to leak. As I said before these things always happen to me way past 10:00 PM. Way to go Carver).

The hose/clamp issue is why we omitted using engine heating on the Hatteras and just run the genny - which doesen't get enough usage as it is!

 

[waymaker]

We had a 6 gal stainless in the 43' and I really liked it. You could cruise without the generator and still have hot water for 48 hours(that was in Fla winter)if you took short showers. The water thermostat was set really hot though.

Tod,
What kind and where did you you get it?

 

[Boatsb]

I was about to replace mine when it stopped working. Looked at the options and was told the recovery time is more important than just capacity. If a 6 gal can keep up with the shower Its pretty good. I was looking at 12-15 gal as it was about the size of the one in ther. Thats when I found the switch. Turned it back on and felt a bit stupid but I did learn a lot.

 

[thoward]

Tod,
What kind and where did you you get it?

Seaward
S700
6 gallons
13w x 19d x 13"h
Stainless Steel
30 lbs.

Combination electric/heat exchanger or electric only
Inner tanks made from Alcoa Alclad aluminum alloy
Hold down brackets welded to inner tank
UL (120 V models) or CE (240 V models) approved
Temperature pressure relief valve
Magnesium anodes available
Large 1/2-inch drain valve
Exteriors are marine galvanized steel
Optional stainless steel or painted aluminum exteriors
Ignition protected
T & P drain tube included
Tempering valves available