On Demand Water Heater

[Play'N Hooky Too]

Consider:

1 BTU is the amount of energy required to raise the temperature of 1 lb of water 1 degree Fahrenheit

1 gallon of water is 8 lbs so to that's 8 BTUs per gallon per degree.

To go from 65 degrees to 120 degrees that's 440 BTUs per gallon

At a flow rate of 1/2 gallon per minute for the hot water that equates to 220 BTUs per minute (13,200 BTUs/hr) or about 3870 watts for an electric on-demand water heater.

The current draw at that rating would be 16 amps/32 amps respectfully for a 240 volt/120 volt system.

[Photolomy]

And a typical shower is 2 gal / min, so multiply that by 4.

[Pascal]

Check out the draw of tankless water heaters... most use 12000 to 24000 Watts Yes thousand not hundred.

https://www.homedepot.com/b/Plumbing...s/N-5yc1vZc1ty

[Play'N Hooky Too]

Our local electric utility has published several articles lately trying to discourage residential installation of these type water heaters for that very reason. Apparently the typical residential electrical grid isn't set up to handle a bunch of 100 amp loads switching off and on like Christmas lights.

[racclarkson@gmail.com]

Much more complex on a boat, but.... I use a timed recirc pump at home that solves long distance from heater to kitchen problem very satisfactorily.

[oscarvan]

Much more complex on a boat, but.... I use a timed recirc pump at home that solves long distance from heater to kitchen problem very satisfactorily.

Seen that done, but it does take energy to keep that line full of hot water.

My diesel pusher came with an on demand propane hot water heater. Because of the way the system was laid out, it took anywhere from 30 (galley) to 50 (shower) seconds to get hot water, especially annoying in the galley. Also, if you shut it off even for just a second it would take a few seconds for the heater to fire up again and you would get a "cold sandwich".... (Absolutely no navy showers).....

I installed a 7 gallon electric tank heater right before the distribution manifold, fed by the on demand heater... It acts as a buffer and brings hot water to the galley in 12 seconds. Still allows for endless "Hollywood" showers for my bride...

This works in residential applications too. The tanks are 3000W....

[racclarkson@gmail.com]

Seen that done, but it does take energy to keep that line full of hot water.My diesel pusher came with an on demand propane hot water heater. Because of the way the system was laid out, it took anywhere from 30 (galley) to 50 (shower) seconds to get hot water, especially annoying in the galley. Also, if you shut it off even for just a second it would take a few seconds for the heater to fire up again and you would get a "cold sandwich".... (Absolutely no navy showers).....I installed a 7 gallon electric tank heater right before the distribution manifold, fed by the on demand heater... It acts as a buffer and brings hot water to the galley in 12 seconds. Still allows for endless "Hollywood" showers for my bride...This works in residential applications too. The tanks are 3000W....

14-25W for 3 hours a day. That’s the point relating to a boat and its limited power supply.

[Tim Powell]

Good point. I can see this will take a little more research on my end. A 20 degree rise sure isn't much
if that's the case.

call Sams when i got my 52 i had a hot water maker at the kitchen sink. But it was short lived i threw it out. the water was not hot enough for coffee and to hot to wash hands kinda usless.
I want to think it was from Hatteras copper pipe and all. It was electric. As for on demand electric ones suck the ones i have seen you have to adjust water flow to control water temp. You know what that means . Cold water or no pressure.

[Photolomy]

14-25W for 3 hours a day. That’s the point relating to a boat and its limited power supply.

That's pretty neat though, for a house. I didn't know that existed.

[madhatter66]

I've read the Bosch water heaters are good and only draw 12amps.

2, 4 or 7gal. the 7 gal has to be hard wired though. The other 2 just plug in. Also not ignition protected so don't install in the engine compartment.

https://www.homedepot.com/p/Bosch-7-Gal-Electric-Point-of-Use-Water-Heater-ES-8/206428468