Water heater

JPGator

JPGator

Active Member
Apr 25, 2019
495
Treasure Coast
Boat Info
2008 Sundancer 40
Engines
Cummins QSB 5.9 425HO
How long does the water heater take to warm up the water for a shower. We’ve never used ours because we mostly use the transom shower and the water is warm enough from the engines or genny running.
For reference we have an Atwood water heater. Also, that warning about hydrogen gas build up. Is that really a concern?
 
If your asking how long using shore power (110v) - I have never timed it, but its not been an issue -- I would guess you would have some warm water in 20min, and a hot tank in less than an hour for sure (they are small tanks). Your comment about warm enough from engines or genny -- those are (normally) two completely different heat sources. The engine will use a coolant loop through the water heater to heat. The generator would provide 110v AC and the electric heating element would provide the heat. So it seem's that you've used both methods for creating hot water.

When you're using 110v AC to heat water, make sure the hot water tank is full of water -- otherwise you will burn out the heating element (PIA to replace in the Atwood). Whenever we arrive at the boat, I run the hot water for several minutes, to help flush out whatever might be in the hot water tank. Then I flip the AC Breaker on -- which starts heating the fresh water that's in the tank.
 
To second what markrsimon said, it shouldn't take long at all to get hot water from shore power. We were out for the day last weekend and came back late in the evening and slept on the boat in our slip. We fixed dinner and the water was still hot from running back to the dock, and so I didn't switch the hot water heater on before bed. I woke up that next morning and flipped it on and had really warm water in ~10 min.

It's always a good practice to flush your hot water before flipping on the breaker, whether using the city water connection or your fresh water tank. This ensures that your tank is full of water and is flushed a bit. Most times when this goes wrong, is after spring commissioning if the water heater was drained and bypassed for winterization and someone forgets to reconnect it and fill the tank by running the hot water side.
 
Gentlemen Thank You,

Just to be clear how do you ensure your hot water tank is full of water? I filled up the fresh water tank but how do I ensure the hot water side is full?
 
Turn on your fresh water pump - which Im assuming you do already - as that gives you the cold water out of your faucets. To ensure hot water tank is full - simply open the hot faucet only - until water comes out. To flush the hot water tank, open the hot faucet and let it run for 5-10min to move water through the hot water tank.

If your docked, with dock water - skip the fresh water pump step.
 
Excellent. We never connect to dock water. We fill and go so I will follow your instructions.
 
As an added point of clarity which was mentioned above.. check to make sure you dont have a heater bypass installed.. typically done during winterization to minimize how much pseudo-antifreeze you dump in. Typically there are 4 hoses connected to the heater.. cold in, hot out, and two hoses off the engine to heat while under way.. if the cold in and hot out are connected - thats a bypass. Given you stated water is warm enough - it could simply be that your cold water is warm due to ambient temps.. So, after a 30-45min engine cruise - is the hot water hotter than the cold?

Can you get a pic of the water heater? Mainly just trying to validate your setup.
 
After running we do get warm, if not hot, water while using the transom shower.

We are a south Florida boat but I will take a picture tonight or tomorrow morning and post.
 
JPGator said:
After running we do get warm, if not hot, water while using the transom shower.

We are a south Florida boat but I will take a picture tonight or tomorrow morning and post.
Click to expand...

That hot water is going to be from the indirect heat circulation from your engine.

A quick and simple test is to turn on the heater and watch the load on your AC panel. If it moves then the element is putting on a load. If not the element may be shorted.

-Kevin
 
KevinC said:
That hot water is going to be from the indirect heat circulation from your engine.

A quick and simple test is to turn on the heater and watch the load on your AC panel. If it moves then the element is putting on a load. If not the element may be shorted.

-Kevin
Click to expand...

I did verify that Kevin. There is a load.
I’ll get you a pic in the am Mark.
 
Here you go Mark
 

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When cruising, my wife and I take showers right after one another. We both enjoy hot, steamy showers and take them as long as the water is piping hot. When it gets cold we stop. We alternate who goes last because that person wipes down the shower stall and cleans the bathroom. In the time it takes to dry off and change into fresh clothes the water heater replenishes its supply of hot water. So......I guessing 10-15 minutes to get back into the comfort range. With restrictive shower wands common on boats, the heaters make hot water at close to the rate you use it up.
 
JPGator said:
Here you go Mark
Click to expand...

That is not what I expected to see. The lower indirect heater feeds are not connected to the system so the engines are probably not heating the water.

The upper red PEX is connected to the outlet and many times there is a mixer valve there also (blends the very hot and cold to set a lower temp - yes this can be done at the faucets but it protects from scalding hot coming out). The lower blue would be feeding the heater. I can see the red PEX valve is on and I am guessing the blue is to. The other valve is a pressure relief valve.

If the system is providing water on the hot water side of the the faucets then water should be flowing through the heater. I would turn it on and give it 15 mins and turn on the hot water at a faucet. It may take a little time for the hot water to fill the lines but the red PEX tube should get hot to the touch.

If not heating check the voltage at the element which is under the little metal cover - be careful as it is 120VAC. If you have voltage and still no heat you will need to pull the element. If it is highly scaled give it a good bath in Vinegar to clean if not take it to HD or Lowes and match it up for a replacement.

-Kevin
 
JPGator said:
Not what you expected to see because something is wrong?
Click to expand...

No, because you were saying the water was hot after running the boat - I thought the engines were providing the heat. I was expecting to see the heater lines from the engine connected. It does not look like the engines are connected - those are the two nipples on the unit without hoses - they would normally be connected in a loop to your engines - much like a heater core in a car.

So, if you are out running do you have your genset and water heater on - if so then it is probably working - just may be taking a little longer to heat the 6 gallons of water. It is possible the element is scaled up and could be cleaned if it takes a long time.

-Kevin
 
I recently timed that it takes ~36 minutes for our hot water heater to heat up a tank of water from a cold start until the heating element switches off (by watching the amp draw).

I tested because when we wake up at anchor, sometimes I want the generator noise going only as long as necessary to give the batteries a morning charge, make coffee, heat the hot water...then shut down and get back to the sounds of nature.
 
KevinC said:
No, because you were saying the water was hot after running the boat - I thought the engines were providing the heat. I was expecting to see the heater lines from the engine connected. It does not look like the engines are connected - those are the two nipples on the unit without hoses - they would normally be connected in a loop to your engines - much like a heater core in a car.

So, if you are out running do you have your genset and water heater on - if so then it is probably working - just may be taking a little longer to heat the 6 gallons of water. It is possible the element is scaled up and could be cleaned if it takes a long time.

-Kevin
Click to expand...

We always run the genset when out but I wasn’t aware they were connected. I’ve never used the water heater on this boat because the transom shower always does the trick.
 
JPGator said:
We always run the genset when out but I wasn’t aware they were connected. I’ve never used the water heater on this boat because the transom shower always does the trick.
Click to expand...

The genset would just provide the 120VAC power to the water heater - nothing else.

-Kevin
 
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