Point of use hot water heaters

[Startracker]

If anyone finds a diesel fired tankless, let me know I keep thinking they have to exist. My last boat used a mini-keg as a hot water tank. Seems to have lasted since '72 and kept the pilothouse warm in the winter too. Just a simple loop from the diesel furnace of the same vintage.
Part of me wants to build a small tank on a circulating system using a diesel fired hydronic heater like the webasto. Stick the most efficient plate heat exchanger in and see what happens.

Also, for those with undersized tanks but good shore power. There are inline electric booster heaters, west marine used to carry them, don't think they ever took off as I got some for like 75% off list. I think from 750w to 1200W, about the size of a small paperback. I had a few but never got around to using them. They increase the temperature by X at a given flow rate, say you're boosting by 20 degrees, still makes a big difference in the length of shower. Like this but smaller and a hell of a lot cheaper. I think I paid around 30$ each.
https://www.homedepot.ca/product/rhe...ter/1001323685

[garyfdl]

Originally Posted by Startracker

If anyone finds a diesel fired tankless, let me know I keep thinking they have to exist. My last boat used a mini-keg as a hot water tank. Seems to have lasted since '72 and kept the pilothouse warm in the winter too. Just a simple loop from the diesel furnace of the same vintage.
Part of me wants to build a small tank on a circulating system using a diesel fired hydronic heater like the webasto. Stick the most efficient plate heat exchanger in and see what happens.

Also, for those with undersized tanks but good shore power. There are inline electric booster heaters, west marine used to carry them, don't think they ever took off as I got some for like 75% off list. I think from 750w to 1200W, about the size of a small paperback. I had a few but never got around to using them. They increase the temperature by X at a given flow rate, say you're boosting by 20 degrees, still makes a big difference in the length of shower. Like this but smaller and a hell of a lot cheaper. I think I paid around 30$ each.
https://www.homedepot.ca/product/rhe...ter/1001323685

Here you go!
https://www.alibaba.com/pla/5KW7KW12...caAq1nEALw_wcB

[Martinini]

I have a 2 1/2 gal water heater and it is to small to do anything but wash your hands or a pot and a couple of dishes! Needless to say I am replacing it with a 6 gallon one so I can at least take a quick shower. Don't waste the money for a tiny water heater.

[smj]

Originally Posted by Martinini

I have a 2 1/2 gal water heater and it is to small to do anything but wash your hands or a pot and a couple of dishes! Needless to say I am replacing it with a 6 gallon one so I can at least take a quick shower. Don't waste the money for a tiny water heater.

Could you please name the brand of the water heater so we know what not to buy? We have the Bosch 2.5 gallon and it will easily produce 2 hot showers, and that’s with shutting it of after the initial heating of the water.

[Martinini]

Steibel, at least I think thats how it's spelled. Don't misunderstand- it works well, just to small. All have a longer than expected recovery time and thats why I'm opting for a larger one.

[garyfdl]

Originally Posted by Martinini

I have a 2 1/2 gal water heater and it is to small to do anything but wash your hands or a pot and a couple of dishes! Needless to say I am replacing it with a 6 gallon one so I can at least take a quick shower. Don't waste the money for a tiny water heater.

I'm inclined to agree. The 2.5 is a 'lav' heater, mainly for washing hands, and maybe your face. That's partly why I'm opting for the 4 gal. Set at it's highest, I'm guessing there will be enough water for a warm(ish) shower (or two) and to rinse dishes.

[smj]

Originally Posted by garyfdl

I'm inclined to agree. The 2.5 is a 'lav' heater, mainly for washing hands, and maybe your face. That's partly why I'm opting for the 4 gal. Set at it's highest, I'm guessing there will be enough water for a warm(ish) shower (or two) and to rinse dishes.

Guess it all depends on how much water you need for a shower? As I’ve said, the 2.5 is plenty for 2 showers for my wife and myself. The 4 gallon for us would only mean a longer heating time and wasted hot water!

[garyfdl]

Originally Posted by smj

Guess it all depends on how much water you need for a shower? As I’ve said, the 2.5 is plenty for 2 showers for my wife and myself. The 4 gallon for us would only mean a longer heating time and wasted hot water!

I 'weigh in' at just over 1/8th of a ton (US), so I might need a little more than the average person to get wet...

[smj]

Originally Posted by garyfdl

I 'weigh in' at just over 1/8th of a ton (US), so I might need a little more than the average person to get wet...

4 gallon it is!!!!!!

[garyfdl]

Originally Posted by smj

4 gallon it is!!!!!!

LOL

[thataway41]

Originally Posted by valhalla360

Again what is the temp of the fresh water tank (and also the hot water tank)?

Assuming the fresh water tank is 60F and back calculating, the hot water tank would need to be around 213F. Actually a little less as there would be some recovery from the heater element running but not a lot with a small 1200w heater......

I would be surprised if there isn't a fail safe far lower than the boiling point

I figured that there would be some objection: We live in Florida, where the ambient temperature of the water is far higher than 60*. The max temp. of our Bosch 2.5 gallon is 140* (some others have note closer to 120*, but you can turn the thermostat past the soft stop.). We are the only ones to use the galley and thus avoid any scalding temperature water on our hands. The hot water to the head, only goes thru the mixing valve and hot water tap. Only the "hot" tap is opened for shower. Since we are recovering "sailors" we took showers on the boat with minimal amounts of water.

There is no recirculating. The "dead" space in 1/2" water hose was about 2' each to shower and the shower mixing valve. The refresh time is very short--about 10 minutes. (element is 1440 watts) Being ex-sailors, we are very frugal with usage water for showers. It works fine for us.

When we were in Northern Climes (Alaska), we had an 11 gallon typical water heater on our Cal 46. The Water heater was close to our shower in the aft cabin, so no real waste of water there, but we did put in a re-circulating valve which manually returned the water for the galley and forward head/shower--about a 20 foot run from the water heater. It took about a minute to get to good shower temperature. That water would have been wasted if no recirculating system. At our home, we have a timer controlled recirculation system, so that there is always hot water at the selected taps. (valves under the counters control which baths have the recirculating system at any one time). That water heater was also heated in series with the returning hot water of the hydronic diesel fired 45,000 BTU boat heating system. The re-circulation was for retention of water, not retention of heat.

[valhalla360]

Originally Posted by thataway41

I figured that there would be some objection: We live in Florida, where the ambient temperature of the water is far higher than 60*.

Not so much an objection as a clarification.

Without the understanding of what the incoming fresh water temperature is, the resulting claims of how many gallons of hot water are available can be very misleading.

[thataway41]

Originally Posted by valhalla360

Not so much an objection as a clarification.

Without the understanding of what the incoming fresh water temperature is, the resulting claims of how many gallons of hot water are available can be very misleading.

True, and thanks for pointing that out. Hopefully each person who reads responses can use the information and his own perimeters to determine if the 2.5 gallon water heater is a good match for his own vessel. This not only depends on water temperatures, but availability of tank water, if the water is re-circulated. and the dead space in the water lines. The mixing valve puts another slant to conservation of both heat and water use.

[Startracker]

Originally Posted by garyfdl

Here you go!
https://www.alibaba.com/pla/5KW7KW12...caAq1nEALw_wcB

Unfortunately they might pitch it as such, but I am extremely skeptical. As a heater to heat a hot water tank via heat exchanger? I do buy that one. However air+HW out of the same unit strikes me as less efficient than a strictly hydronic loop, as you can then run hot water only.

[Martinini]

IF You have the room for and the money for-----------DO YOURSELF A FAVOR AND GET A 6 GALLON HEATER! You will be much happier with the result. Been on my boat for 15 years.