On demand hot water?

[RickB]

If they do not have this water pressure, the water can boil before it leaves the heat exchanger (PV=NRT) ...

Wrong law.

If water in the heater boils it is saturated vapor, it does not follow the ideal gas law. For calculations of the phenomenon you described you must use the steam tables.

The noise you mentioned is from vapor bubbles collapsing as they come into contact with cooler liquid.

 

[FF]

.and both are not very well insulated, so that contributes to their loses??

It just depends on your wallet and the tradeoffs you can accept.

Fridges are crap as the insulation is very thin to create the largest interior volume ,(as the purchaser demands) and the required heating elements to clear the wet insulation and door seals , just happen to NOT be counted in the annual power consumption tag. K street at work.

A Sun Frost is well, insulated , efficient and pricy.

Servelle is the equal for the propane folks.

WE have 240v in our Fl digs but it would have to be rewired for an instant heater.

Far easier to pay ONCE for an insulated tank that only loosed 5-deg a day .

 

[rwidman]

Wow,at what voltage is that AMP figure?


Wow, are they that costly? Sure a lot cheaper here in Thailand

And here they work off of 220v, so less amps I'm sure.

150 amps at 120 volts and 75 amps at 240 volts are the same power (watts). The same amount of energy and will produce the same amount of heat. On a boat, generating either from a battery/inverter setup will draw the same amount of power from the batteries.

You would need a very high capacity battery bank to use such a water heater for more than a couple of minutes without recharging the batteries.

That's about the draw of my microwave but it runs only a couple of minutes for each use.

 

[hollywood8118]

My take on demand water heaters.....

Electric demand WILL NOT WORK on anything less than a big genset. No way to do it with dc.

I have had 2 Paloma demand propane heaters on 2 different boats,, they will supply lots of hot water BUT have serious install issues and they are subject to wild heat fluctuations at low flow.

So serious I bypassed the last one in favor of a 12g marine storage unit... and I never fired the Paloma again.

Marine standard water heaters with a heat exchanger are dirt simple and can be had cheap.. there is ABSOLUTELY no reason not to use one unless space is the issue.


HOLLYWOOD

 

[psneeld]

I'm not sure "never" is the appropriate word...has anyone ever had both in line? The tank to handle the fluxuations (as Bligh pointed out... his choice already had 2 gallons in it) and a preheater (though still expensive for my tastes and probable use) to give closer to limitless hot water?

If we didn't reinvent the wheel...then the only options for a canoe would be what type tree do you carve it out of and humping it on your car roof instead of an aluminum or fiberglass one would be a PIA.

many great ideas have come from forums...not marine manufacturers.

 

[sunchaser]

Some of us don't live in FL. Some of us are quite happy to boat in cooler waters. Some of us have diesel fired boilers for hydronic heat. If so rigged, a hydronic heating system will heat the water in a HW tank while boat is anchored away from shore power. No genset required for this task.

And some of us don't think propane on a boat is a good idea especially with an on demand water heater. Seriously, does anyone think these are a good thing on a toy boat and can point to a happy long term user?

 

[Guinness]

Hello.
I run in to a fellow boater in Maple Bay few days ago looking for moorage, and he had been turned down everywhere because his boat failed insurance survey due to Hot water on demand fuelled by propane. Check with your insurance company and get a ruling in writing before you install that.He had a propane stove and that was fine but they did not accept Hot water on demand fuelled by propane. Just my 2 bits worth. Good luck.

 

[psneeld]

Some of us don't live in FL. Some of us are quite happy to boat in cooler waters. Some of us have diesel fired boilers for hydronic heat. If so rigged, a hydronic heating system will heat the water in a HW tank while boat is anchored away from shore power. No genset required for this task.

And some of us don't think propane on a boat is a good idea especially with an on demand water heater. Seriously, does anyone think these are a good thing on a toy boat and can point to a happy long term user?

I agree but that may be for only half of us...

For my boating too...the $$$ would be of much better use going into a hydronic system....

but I still think it is doable and remotely useful...

 

[Baker]

The danger to the engine is very minor , I have never seen or heard of it happening in 55 years , so far.

The DANGER of a leak of the engine coolant into the fresh water , which could poison the FW does in theory exist.

The solution is a double wall heating element , common in house alt energy setups , probably too expensive for most boaters.

Simple , if you TASTE anti-freez , dont drink the water.

FF...add this to your records. I had a sailboat with a heating loop from the engine through the water heater. Somewhere in that loop was a clog. And when it backed up to the engine, it caused some sort of bypass to open and the cooling water to continue on its way around the restriction(raw water system...Volvo 2002 diesel) and not cooling the engine properly. The engine would overheat at anything over idle power. Yet there was water happily flowing out of the exhaust outlet. It was very confusing to diagnose. I managed but it took my a week of going though every single part of the cooling system until I got to the water heater loop....bypassed it and all was well.

 

[O C Diver]

FF...add this to your records. I had a sailboat with a heating loop from the engine through the water heater. Somewhere in that loop was a clog. And when it backed up to the engine, it caused some sort of bypass to open and the cooling water to continue on its way around the restriction(raw water system...Volvo 2002 diesel) and not cooling the engine properly. The engine would overheat at anything over idle power. Yet there was water happily flowing out of the exhaust outlet. It was very confusing to diagnose. I managed but it took my a week of going though every single part of the cooling system until I got to the water heater loop....bypassed it and all was well.

Sounds like it wasn't plumbed correctly (not surprising on a Volvo ). All the installs I've seen have valves on the engine to isolate the HW heater loop in the event of a leak. On my charter boat we have the same type of loop to provide cabin heat. I close both valves during the summer to turn the heat off, without any effect to the engine.

Ted

 

[Baker]

After I gave up, if went to the Volvo dealer and told him what was going on. He asked if I had a water heart loop. And then said to isolate it. I then asked why I was getting good water flow...and he said there is a bypass in the system...I don't know what it is protecting other than the pump and maybe excessive pressure. Anyway, he knew exactly what it I was so it was probably a Volvo deal...

 

[FF]

Some of us have diesel fired boilers for hydronic heat. If so rigged, a hydronic heating system will heat the water in a HW tank while boat is anchored away from shore power. No genset required for this task.

No genset required , GREAT!! How is this performed with no electric?

I have a Dickinson furnace that circs water for finned heat tubing that is thermosyphon ,no circ pump, A first I think on a 33ft boat .

But I can not figure out how to heat tanked hot water with no electric .

How is it done?

 

[sunchaser]

No genset required , GREAT!! How is this performed with no electric?

I have a Dickinson furnace that circs water for finned heat tubing that is thermosyphon ,no circ pump, A first I think on a 33ft boat .

But I can not figure out how to heat tanked hot water with no electric .

How is it done?

Well FF, I guess my semantics were not quite perfect - the battery bank runs the 12V circulating pump and HX fans, as required.

 

[bligh]

Some of us have diesel fired boilers for hydronic heat. If so rigged, a hydronic heating system will heat the water in a HW tank while boat is anchored away from shore power. No genset required for this task.

No genset required , GREAT!! How is this performed with no electric?

I have a Dickinson furnace that circs water for finned heat tubing that is thermosyphon ,no circ pump, A first I think on a 33ft boat .

But I can not figure out how to heat tanked hot water with no electric .

How is it done?

Post or send me a schematic of your radiator piping and I will figure it out. It can definitely be done with your system.

 

[FF]

Post or send me a schematic of your radiator piping and I will figure it out. It can definitely be done with your system.

It would need to be a sepaerate system as it took 2 -3 years of tinkering the get a gravity thermo syphon to function .

The trick was to replace elbows created with 2 -45 fittings with slow ells from the refrigeration folks. The 3 or 4 inch radius helped the water flow as the difference in water weight when heated to 135F to 140F in a 75F cabin is really small.

Even went so far as lowering the feet of the furnace for a couple of inches in water lift height.

With a different smoke pipe that had a water jacket , it would be easy to pipe water to the HW line , and capture some more free heat.

 

[sunchaser]

It would need to be a sepaerate system as it took 2 -3 years of tinkering the get a gravity thermo syphon to function .
.

If you boated in colder climes you'd be electrically pumping that fluid in about 30 minutes.

 

[FF]

If you boated in colder climes you'd be electrically pumping that fluid in about 30 minutes.

Having lived aboard for almost 23 years ,and been frozen hard for over 6 weeks
ANY electric anything is dead when the juice in the marina is off for a week or more.

So far they do not tax or have an off switch for GRAVITY .

Have fuel? Have Gravity ? We have central heating!

 

[Earl34Mainship]

Wilson... nice American Optics Aviator sunglasses... Army issue a few years back...