I have a Kuuma 6 gallon water heater. How long should it take to heat up water (120º) with coolant temp between 160 - 180?
How long to heat water
- Thread starter Hayden Watson
- Start date
My Yanmar 3 GMF takes about ten minutes to heat the 6 gallon Seaward water heater in my boat from "everything cold" state. Your time will vary with the coolant flow scheme on your boat. Your cabin heater may be adding enough back pressure into the coolant flow circuit that it could be slowing the flow..?? collapsed or kinked hoses? Ya might be able to rig a bypass of the cabin heater (get it out of the circuit) to see if that is the problem ..?
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Wow. I replaced my thermostat yesterday because the engine would not get more than 140º under load. it now heats up to 180 which is the thermostat rating. With my IR thermometer the WH inlet hose reads 159º and the outlet hose is 147º but after running for an hour the water had only gone from 60º to 80º. My WH is a Kuuma 6 gal and I have been told that the heat exchanger inside is a "U" shaped loop of aluminum double wall tubing. I have scoped the inside of the tank and the tube is clear. It seems that if the problem was restricted flow then the outlet temperature would be close to water temperature.
Hayden. You need more info to decide if it may be a broken system.
Your info reports coolant is loosing 12º passing through the WH. We assume it is transmitting that to the water in the tank. It is taking an hour to change the water temp 20º. This is measured where? At the faucet, I guess. What happens between the WH and the faucet for the hot water? Is there a mixing valve in the system? Do you know the efficiency of the Kuuma WH? Perhaps the heat exchange is programmed to be slow? How old is the WH?
I do not know how long it takes to get hot water. I know that water in the system takes a while to get hot water to the faucet. I know that the insulation around the tank keeps hot water available over night.
Your info reports coolant is loosing 12º passing through the WH. We assume it is transmitting that to the water in the tank. It is taking an hour to change the water temp 20º. This is measured where? At the faucet, I guess. What happens between the WH and the faucet for the hot water? Is there a mixing valve in the system? Do you know the efficiency of the Kuuma WH? Perhaps the heat exchange is programmed to be slow? How old is the WH?
I do not know how long it takes to get hot water. I know that water in the system takes a while to get hot water to the faucet. I know that the insulation around the tank keeps hot water available over night.
Heat transfer is a function of flow rate and temperature - your info indicates only that the temp delta shows some transfer. A low flow rate which is a function of engine speed and specifically water pump speed can cause the situation you describe. Are you running the engine at idle speed while testing?
Just be sure not to watch it. It always takes longer if you do.
- Water temp was taken at the outlet hose at the tank and at the sink to confirm. There is no mixing valve in the system.
- If I knew the flow rate of the coolant I could calc how many BTU's were being passed but a 12º delta seems fairly decent.
- The raw water heat exchanger drops the primary loop from 160º down to 85º but it is a double flow multi-tube system that would obviously be much more efficient.
- Using a borescope to look inside the tank I have confirmed that there is no scale on the exchanger pipe in the tank and that it is a "U" shaped pipe.
- Tank is about 10 years old and I have never been able to get hot water from the engine.
- Water fully heats with electric element in about 30 minutes.
- Talked to Kuuna engineering and they say that it should get fully hot in well under an hour.
- For the first 30 minutes I ran in gear at 1900 rpm which is full cruise speed on my M25XP. The next 30 minutes was at 1400 rpm in gear. Engine temp stayed constant at 180º
- It could be that Justin_NSA has the answer. The pot was being watched very closely
Yes. It is a pain about the watched pot.
Your issue may be the coolant plumbing to the system not the WH.
- 10 years old does not seem old in boat years.
Your issue may be the coolant plumbing to the system not the WH.
Hayden, what you don't know is if you have a water heater problem or a coolant flow problem. So why not test both to isolate what is wrong? Plumb the water heater directly into the flow stream of coolant just before the raw water heat exchanger. Just cap off or use a jumper hose for your bypass loop temporarily. If the water heater heats right up when the thermostat opens you know it works fine and that your problem is flow rate of coolant in your bypass loop. Another option is bypass the cabin heater and see if the hot water heater improves performance. Is the cabin heater providing any heat? Try these this afternoon and let us know what you find.
I tested the flow yesterday by removing the return line.
Here are links to videos of flow at idle and 1600 rpms. Testing the flow this way shows the flow at closed thermostat but because it bypasses the thermostat the coolant temperature could not get above 120º.
Idle: https://www.screencast.com/t/rOoXrkEtq4S
1600 rpm: https://www.screencast.com/t/DIaSbdq9WOSw
I reconnected the system and motored at 5 knots (1900 rpm @ 180º) for one hour. The heating was better but still not as fast as others have indicated. In one hour the water temperature went from 60º to 90º.
Here are links to videos of flow at idle and 1600 rpms. Testing the flow this way shows the flow at closed thermostat but because it bypasses the thermostat the coolant temperature could not get above 120º.
Idle: https://www.screencast.com/t/rOoXrkEtq4S
1600 rpm: https://www.screencast.com/t/DIaSbdq9WOSw
I reconnected the system and motored at 5 knots (1900 rpm @ 180º) for one hour. The heating was better but still not as fast as others have indicated. In one hour the water temperature went from 60º to 90º.
Hayden. It sure looks like you have adequate flow. Who knows.. You may need to run you system longer than others. Perhaps the engine you have runs cooler than others. When I get to my boat this month I will run and test my system.
Heat exchange pipe might be coated with "sludge" that would preclude adequate heat transfer?
Is the heat exchanger copper or aluminum in the hot water heater? You might discuss cleaning it ultrasonically or with some acid cleaner -- UNLESS it's aluminum or isn't in good shape.
Is the heat exchanger copper or aluminum in the hot water heater? You might discuss cleaning it ultrasonically or with some acid cleaner -- UNLESS it's aluminum or isn't in good shape.
Thanks for the replies.
jssailem: The temp gauge on the engine panel read 180º and I was getting readings of 165º at the inlet hose with my IR thermometer
jviss: I purchased and installed the current heater in 2006. It has never heated water well from the engine but gets fully hot on 120v in about 30 minutes.
SV: A couple of years ago I bought a gallon of commercial boiler de-limer and cleaned out the tank. I have used my borescope to look inside and it is clean aluminum. I have talked to the Kuuma engineer and have been told that the heat exchanger is an aluminum tube in a tube design. One tube is placed inside another with a small gap between. the two tubes are then bent to the proper shape which puts much of the tubes into contact. the outer tube is welded to the tank wall and the inner tube extends out of the tank and has a threaded coupling added. This is done so that if there is a leak in either tube the fluid will leak out instead of cross contaminating the water supply with antifreeze.
jssailem: The temp gauge on the engine panel read 180º and I was getting readings of 165º at the inlet hose with my IR thermometer
jviss: I purchased and installed the current heater in 2006. It has never heated water well from the engine but gets fully hot on 120v in about 30 minutes.
SV: A couple of years ago I bought a gallon of commercial boiler de-limer and cleaned out the tank. I have used my borescope to look inside and it is clean aluminum. I have talked to the Kuuma engineer and have been told that the heat exchanger is an aluminum tube in a tube design. One tube is placed inside another with a small gap between. the two tubes are then bent to the proper shape which puts much of the tubes into contact. the outer tube is welded to the tank wall and the inner tube extends out of the tank and has a threaded coupling added. This is done so that if there is a leak in either tube the fluid will leak out instead of cross contaminating the water supply with antifreeze.
Hayden:
So you have an aluminum tube heat exchanger. There I wouldn't try to clean it out with acid. Cleaning out the main heater tank, may be a different issue with a decalcifier through the thin tubes of the heat exchanger. (I'm not sure that an aggressive boiler cleaner is such a good idea in an aluminum tank.
I guess, unless you're tired of going though this on this forum...
As you know, the thermostat opens and closes to allow water to circulate through the heat exchanger. Your Straights of Juan del Fuca water is much cooler than (say) Florida, but that's not this issue as much as your engine's load and RPM speed. You fixed your engine's thermostat so it opens and closes (letting the engine operate more evenly at 180° vs. opening MORE and having the operating temperature lower). Without getting to the discussing enthalpy and conservation of energy, that shouldn't be the issue anymore.
To really help you further, or talk with the hot water heater manufacturer, I suggest:
Get the engine is up to temperature, and running at moderate RPM/Loads, so that you have more "like continuous flow" through the heater loop. Prepare a little chart of those things with the water temp that you have in the tank as it supposedly "heats-up". You want the time being shown on one of the sides of the chart. Note the ambient temperature of the hot water heater compartment (more or less).
I'm assuming that your hot water isn't being cooled before it reaches your sink or shower? But lets measure the hot water close to the source and/or make sure it's not being "mixed down".
In practice, under engine exchanger, the hot water in the tank should be close to "dangerously" hot unless you're careful or the temp regulating valves because the electric unit is regulated to keep the tank a lower temp then the "dumb" heat exchanger from the hotter engine coolant loop.
So you have an aluminum tube heat exchanger. There I wouldn't try to clean it out with acid. Cleaning out the main heater tank, may be a different issue with a decalcifier through the thin tubes of the heat exchanger. (I'm not sure that an aggressive boiler cleaner is such a good idea in an aluminum tank.
I guess, unless you're tired of going though this on this forum...
As you know, the thermostat opens and closes to allow water to circulate through the heat exchanger. Your Straights of Juan del Fuca water is much cooler than (say) Florida, but that's not this issue as much as your engine's load and RPM speed. You fixed your engine's thermostat so it opens and closes (letting the engine operate more evenly at 180° vs. opening MORE and having the operating temperature lower). Without getting to the discussing enthalpy and conservation of energy, that shouldn't be the issue anymore.
To really help you further, or talk with the hot water heater manufacturer, I suggest:
Get the engine is up to temperature, and running at moderate RPM/Loads, so that you have more "like continuous flow" through the heater loop. Prepare a little chart of those things with the water temp that you have in the tank as it supposedly "heats-up". You want the time being shown on one of the sides of the chart. Note the ambient temperature of the hot water heater compartment (more or less).
- What's the temperature at the of the take-off of the heater loop at the engine?
- What's the temperature at the supply side of the hot water heater exchanger?
- What's the temperature at the discharge side of the hot water heater exchanger?
- And for funnzies, what's the temperature at the return side where the line runs back into the engine loop?
I'm assuming that your hot water isn't being cooled before it reaches your sink or shower? But lets measure the hot water close to the source and/or make sure it's not being "mixed down".
In practice, under engine exchanger, the hot water in the tank should be close to "dangerously" hot unless you're careful or the temp regulating valves because the electric unit is regulated to keep the tank a lower temp then the "dumb" heat exchanger from the hotter engine coolant loop.
Ever see these coffee mugs with a double wall, metal on the inside and metal on the outside, they keep ice cold for 24 hours in a car in the hot sun in the south. I have verified this fact repeatedly. So telling us that your water heater is a double tube design kind of sounds like a very well insulated mug that prevents heat transfer. The comment about the tubes in contact when they are bent is likely just along a tangent line so minimal conduction is taking place and you are relying on radiant heating and convection across the insulating layer between the tubes. The Kuuma also seems to use 5/8 fittings (ref. the Kuuma manual) where other brands use 3/4 so your flow rate is lower than others. The hoses in your video seem small compared to the ones I've seen on other vessels. Other heaters use a serpentine style heat exchanger that provides much more surface area for heat transfer than a simple half moon loop. I would plumb it into your main coolant flow before the engine HX to maximize the flow and heat transfer, but not at the expense of restricting flow to the heat exchange if that requires 3/4 hoses. I get scalding hot water when powering under load in about 15 minutes.
jibes138
I think that the contact or lack thereof is probably the root of my problem but this is the same design as used in all Kuuma and relabeled West Marine heaters made by them. I can understand the safety aspect with antifreeze running into the bilge instead of the potable water. I am thinking that when mine got bent it must have not gotten as much contact as typically happens. Practical Sailor tested this heater and reported that it performed better than average so I must have just gotten a lemon. The work I have done this week has improved it because I got 30º increase in 1 hour where previously I would take 3 hours.
The hose size you see is 3/8" and is only for the first couple of feet and then the rest of the circuit is 5/8". On the M25XP, the bypass ports are 3/8" so it needs to start and end with that if I use the bypass. I prefer to keep it in the bypass as a safety measure. much shorter run of the critical hose and if I get a leak in the bypass loop I can cut out 6" of good hose and return to straight bypass hose eliminating any problems in the heaters.
I think that the contact or lack thereof is probably the root of my problem but this is the same design as used in all Kuuma and relabeled West Marine heaters made by them. I can understand the safety aspect with antifreeze running into the bilge instead of the potable water. I am thinking that when mine got bent it must have not gotten as much contact as typically happens. Practical Sailor tested this heater and reported that it performed better than average so I must have just gotten a lemon. The work I have done this week has improved it because I got 30º increase in 1 hour where previously I would take 3 hours.
The hose size you see is 3/8" and is only for the first couple of feet and then the rest of the circuit is 5/8". On the M25XP, the bypass ports are 3/8" so it needs to start and end with that if I use the bypass. I prefer to keep it in the bypass as a safety measure. much shorter run of the critical hose and if I get a leak in the bypass loop I can cut out 6" of good hose and return to straight bypass hose eliminating any problems in the heaters.
Just out of curiosity, Hayden, is the electric element lower in the heater than the top coolant connection? Just thinking that if there is a trapped bubble (potable side) that is small enough to have the electric element heating the water but the heat exchanging tube is not fully covered, heat transfer area for coolant would be limited and it would kinda display those symptoms.. ?? Have you lifted the lever on the TP safety and bled the tank from there (tank cold).. (that should be close to highest point) ..