How long for hot water?

Hayden Watson

Hayden Watson

.
Apr 5, 2009
3,171
Catalina '88 C30 tr/bs Oak Harbor, WA
How long should it take to make hot water when running the engine?
I have a Kuuma water heater on my 1988 C30 which is plumbed to the engine through the thermostat bypass hose but it is REALLY SLOW to heat. I tested it yesterday with a digital non-contact thermometer. The inlet hose from the engine was about 140º but after a 40 minute run, the hot water coming out of the water heater was only 6º warmer than the water going in.:cussing:
The really weird thing is that I have a RedDot heater that is in this same loop that uses the engine coolant after it leaves the water heater and it heats the cabin quite nicely. It seems like the heat exchanger in the water heater exchanger has insulation around it.
 
Don S/V ILLusion

Don S/V ILLusion

.
Sep 25, 2008
7,523
Alden 50 Sarasota, Florida
Hayden Watson said:
The inlet hose from the engine was about 140º but after a 40 minute run, the hot water coming out of the water heater was only 6º warmer than the water going in.
Click to expand

I can't make sense of this. I'm assuming the heater is not energized as you are running the engine to produce hot water. As such, the water being pumped out of the engine at 140 deg to the heater cannot increase in temp as it flows through a non-energized heating element.

What am I missing?
 
Jackdaw

Jackdaw

.
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Don S/V ILLusion said:
I can't make sense of this. I'm assuming the heater is not energized as you are running the engine to produce hot water. As such, the water being pumped out of the engine at 140 deg to the heater cannot increase in temp as it flows through a non-energized heating element.

What am I missing?
Click to expand
Don,

He's talking about the potable water side only warming 6 degrees, not the engine water in the heat exchanger.
 
Hayden Watson

Hayden Watson

.
Apr 5, 2009
3,171
Catalina '88 C30 tr/bs Oak Harbor, WA
Jackdaw said:
Don,

He's talking about the potable water side only warming 6 degrees, not the engine water in the heat exchanger.
Click to expand
Jackdaw is correct. I will try to paint a better word picture. I will use the following abbreviations: heat exchanger on water heater (HE), potable water (P). All references to in and out are at the water heater.
The test started with cold water in the water heater at 73º. The engine anti-freeze heated to 140º within 5 minutes. After 40 minute of motoring at 6 knots the temperatures at the potable water heater connections were as follows.
HE-in = 140º
HE-out = 137º
P-in = 73º
P-out = 80.4º

There is a RedDot cabin heater in-line downstream from the hot water heater. Its inlet and outlet temperatures were 137º and 124º.

It seams really strange that the water/water exchange in the hot water tank only pulled 3º from the antifreeze when the water/air exchange in the cabin heater pulled 13º.
 
Stu Jackson

Stu Jackson

.
Feb 26, 2004
23,102
Catalina 34 224 Maple Bay, BC, Canada
It takes our M25 engine 45 minutes at cruising speed to make hot water.

The heat excahnge coefficient between water and air and water and water is different.
 
Jackdaw

Jackdaw

.
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Do you have hard water? The heat exchanger might be calcified.
 
Bob S

Bob S

.
Sep 27, 2007
1,805
Beneteau 393 New Bedford, MA
Stu,
How hot is it after 45 minutes? I never timed it but my water can get too hot after running the engine guessing 45 minutes to an hour. I should probably add a mixer valve for safety. There has been posts on the subject. My galley faucet is the stem type so when I turn it on it's already mixing. I did replace the hoses going from the engine to the back of the water heater last season. i noticed they where cracked from age when I was mounting SPX5 autopilot computer behind the cabinet. You have to remove the four draw cabinet to access the back of the water heater. I'd recommend checking them out. If they spring a leak they be spewing antifreeze. That's one of those out of sight out of mind things that can happen on our boats. I'm sure there is a write up on the C34 site on this. You guys are pretty thorough ;).
 
Hayden Watson

Hayden Watson

.
Apr 5, 2009
3,171
Catalina '88 C30 tr/bs Oak Harbor, WA
Jackdaw said:
Do you have hard water? The heat exchanger might be calcified.
Click to expand
I have been wondering if it might be a calcification problem because it seems to be the only way to insulate the exchanger. I think that I might pull the electric heating element and see if I can see the heat exchanger through the hole. any suggestions as to how to remove any buildup?
The weird thing is that the electric element will heat the water in about 30 minutes. I would think that if one was calcified the other would be too.
 
Jackdaw

Jackdaw

.
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Hayden Watson said:
I have been wondering if it might be a calcification problem because it seems to be the only way to insulate the exchanger. I think that I might pull the electric heating element and see if I can see the heat exchanger through the hole. any suggestions as to how to remove any buildup?
The weird thing is that the electric element will heat the water in about 30 minutes. I would think that if one was calcified the other would be too.
Click to expand
Depends on how often it was used.

There are treatments for that; same as home water heaters. Most hardware stores sell them.
 
Hayden Watson

Hayden Watson

.
Apr 5, 2009
3,171
Catalina '88 C30 tr/bs Oak Harbor, WA
What brand of water heaters do you have? Can anyone with a Kuuma/Force-10 heater tell me know long it take to heat water with the engine?
 
You must log in or register to reply here.

Top Bottom