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Old 20-02-2013, 06:05   #1
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We are gobbling up the kWh and spending lots of money at $.40 per kWh over the winter. We live aboard and I am analyzing the power usage for the umpteenth time. I am wondering whether with the water heater it would be better to turn on the breaker once a day for a while or to just leave the water heater on? I know at home most of us would never turn off a water heater; you just leave it on all the time and have hot water when you need it.

What's the general conclusion on a boat? Should you just leave it on, or is it cheaper to heat once a day? We do use the shower, but if we heat it once a day it does seem to be hot enough in the AM for a shower, but of course then you are using a higher mix of "hot" and you probably use up the whole heater tank and then start from scratch on reheat.

Thoughts?
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Old 20-02-2013, 06:17   #2
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Re: Water Heater - more efficient to turn off or leave on?

We lived aboard for five years before we started cruising...

Our hot water heater usually heats in bout two hours and keeps the water very hot for about 24 hours.

Leaving the breaker on will allow the heater to cycle sevearl times thoughout the day, thus using more electricity.

So if you goal is to save money, try running the hot water heater late evening for about 1-2 hours every day and see if that reduces your bill and gives you enough hot water for showers in the morning.

Good Luck!
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Old 20-02-2013, 06:31   #3
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Greetings,

As a fellow live aboard, I've done both. Turning it on 30 mins or so before you need it provides hot water, but you're right about using more hot in the mix, making the end of a long or multiple showers a little chilly. The power savings can be significant.

My 11 gallon marine hot water heater is my largest power draw onboard. During the winter, the bilge it resides in can get pretty chilly - much colder than where most homes have the water heater installed (basement, garage, or closet). So, it has much higher heat loss for storing heated water. This causes the heater to cycle more often during the winter.

I'm actually thinking of installing a timer on my water heater to kick it on about an hour before the alarm clock goes off in the morning, turn off, then kick back on for an hour or so in the evening.

Later,
NJ
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Old 20-02-2013, 07:18   #4
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Re: Water Heater - more efficient to turn off or leave on?

At $0.40 per KWh, $1000 of solar panels would save about $1 per day during winter and about $2 per day during summer, at the OP's latitude.
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Old 20-02-2013, 07:32   #5
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Quote:
Originally Posted by neptunesjester View Post

I'm actually thinking of installing a timer on my water heater to kick it on about an hour before the alarm clock goes off in the morning, turn off, then kick back on for an hour or so in the evening.

Later,
NJ
Sounds like a good idea. I hate having to get up two hours before a shower. I'm going to try the 2-hours at night schedule.

I wonder, if you leave one on all the time what percentage of the time it is "cycling," or running, when no water is being used? Any idea? I'm guessing 10 minutes an hour, but I have no real info on that.
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Old 20-02-2013, 07:34   #6
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Re: Water Heater - more efficient to turn off or leave on?

How would an on demand water work into this ??
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Old 20-02-2013, 07:36   #7
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Re: Water Heater - more efficient to turn off or leave on?

Quote:
Originally Posted by PamlicoTraveler View Post
... Should you just leave it on, or is it cheaper to heat once a day? ...
Yes, it will be cheaper to turn it off, when hot water is not required; but it may increase the danger of bacterial growth.

Caution: The recommended temperature for an electric storage-type water heater is 60 C (140 F). Any hotter, you risk the danger of scalding. However, a set temperature of at least 60C (140F) is required for the reduction of legionella & other bacteria.

If your hot water tank is insulated to R-10 or less, consider installing an insulation jacket or blanket, particularly if it is located in an unheated area such as the bilge or cockpit locker. Install insulation on the sides and top of the tank. Cut the insulation to leave holes for the pressure relief valve, thermostat, and plumbing pipes. Also insulate hot water pipes/hoses to reduce heat loss from the hoses themselves.
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Old 20-02-2013, 07:36   #8
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At $0.40 per KWh, $1000 of solar panels would save about $1 per day during winter and about $2 per day during summer, at the OP's latitude.
We have 2-80 watt panels, but I expect we get 10-12 amp hrs a day at best from them. A water heater at 110v probably uses 1,500 watts when running...so 500 ah? Anyway, I doubt the panels are helping much.
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Old 20-02-2013, 07:44   #9
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In the winter the lost heat from the hot water heater goes towards heating the interior of the boat, so not really lost energy. I would keep water heater on in this situation.
High electrical costs most likely due to space heating requirement in winter, assuming you are using electric space heater.
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Old 20-02-2013, 08:18   #10
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Re: Water Heater - more efficient to turn off or leave on?

For the last 20 years we have turned the hot water heater off most of the day, turned it on in the evening to heat water for dishes and showers and then turn it off again when finished. Not only has this saved us on electricity used but it seems to have prolonged the life of the heater considerably. The one on our former boat is still working for the current owner after 17 years of use. It still works and looks like new. Chuck
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Old 20-02-2013, 08:39   #11
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Re: Water Heater - more efficient to turn off or leave on?

Not all water heaters are the same. I just switched out an 11-gallon Force 10 for a 6-gallon Isotemp. The Force 10, which was poorly insulated, used a 1,500-watt heating element. The Isotemp, which has substantial insulation, uses a 750-watt element. I'm much more inclined to leave the Isotemp on throughout the day because it draws significantly less power.
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Old 20-02-2013, 08:47   #12
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Re: Water Heater - more efficient to turn off or leave on?

Just recently gone to an on demand from Eco Temp. Hot water when away . Haven't figured the cost savings, but the avalablety is what we were looking for.
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Old 20-02-2013, 08:55   #13
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Re: Water Heater - more efficient to turn off or leave on?

Basic laws of thermodynamics say that more energy will be lost through the walls of the heater if it is left on at temperature 24/7 than if it is turned on once a day just long enough to bring it up to temperature.

The question is if the difference in heat loss is worth having to turn it on and back off once per day. If the water heater is well insulated then probably not. Putting it on a timer might be the thing to do. It probably won't be long before the timer pays for itself in energy savings.
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Old 20-02-2013, 09:00   #14
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Re: Water Heater - more efficient to turn off or leave on?

Okay, I'll give the scientific POV or at least attempt that:

If you want to save on the energy bill, you can only do so significantly by:

- reducing the amount of hot water you use.
- having a top notch water heater with good insulation.
- matching the size of the water heater with the amount of water used.

Let me expand on that a little bit: the insulation of the water heater is eating up some of the energy consumption. When you want hot water all day long, there is no way around this but when you only want hot water in the morning, you can use a timer switch. In Europe, many electric water heaters have that.

Like Gord wrote, do not use any regime in which the water does not get boiling hot. Doing that might kill you with Legionnaires bacteria (neck cramp, nasty way to die...)

cheers,
Nick.
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Old 20-02-2013, 09:22   #15
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Re: Water Heater - more efficient to turn off or leave on?

It costs less per month to only turn the marine heater on 30-40 minutes before use and turn it off either during or just after use. Standby heat loss will account for roughly 65-70% of the hot water portion of an electric bill, perhaps a bit more in cooler locations. When I had a hot water heater, leaving it on 24/7 just about doubled my electric cost. I then switched to using it at a demand heater and dropped the electric bill by $15 a month.

Additional insulation around the water heater will help reduce standby loss.
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