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Old 02-17-2010, 12:36 PM   #1
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Post Water heater efficiency GAS vs ELECTRIC in Landyacht class A

We have the factory hot water heater in our 2000 Land Yacht 33' and am curious about the best effeciency for its use.

When connected to electric which way wil provide fastest and or cheapest hot water: GAS or ELECTIRC or (is both possible and would that provide faster recovery after shower?).

I have been just running electric unless dry camping and Ido notice the electric bill is pretty high. I had the hotwater heater checked at Camperworld a couple of months ago and they said the element was OK and they also adjusted the GAS flame for best.

Any advice or council would be appreciated.

Thanks
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Old 02-17-2010, 01:15 PM   #2
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Easy questions first. Yes you can run both at once and get more hot water faster. Either one by itself produces about the same amount of hot water per hour.

Efficiency wise I use 99% for the electric and 75% for the gas, not considering the heat loss through the tank wall which is the same either way.

There are 3143 BTUs in a kWh of electricity, and about 91,250 BTUs in a gallon of propane.

So allowing for efficiency you get 3112 BTH from a kWH, and 68,437 BTU from a gallon of propane.

68,437 divided by 3112 is 22.

That means that if the price of a gallon of propane is less than 22 times the price of a kWh of electricity, the propane is cheaper.

At one of the nearby Flying J plazas, the price of propane is $3.119 a gallon. So if that's your propane price, electric is going to work out better if it's below 14.5 cents a kWH. Electric rates vary depending on where you are. We pay around 12 cents, and people a few miles closer to the city pay around 8 cents.

Now, the local LP dealer right down the road from us will sell propane today for $1.81 a gallon, delivered, as long as you are having them fill a tank of 500 gallon capacity or greater. Dividing by 22 that puts the break even point at 8.2 cents a kWH for electric. The price goes up or down a few cents if you have larger or smaller tanks, and though I didn't ask them on the phone today, usually they'll fill a 100 gallon tank for about 20 cents more a gallon than the 500 gallon rate. So, if you're staying in one spot for a while it pays to have them bring a tank out.

I figure the modern furnaces are a little more efficient than the water heater so I'd use 25 as a divisor for the furnace instead of 22.

Of course if your electric service isn't metered and you're just paying by the day it's always going to be cheaper to run electric.
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Old 02-17-2010, 11:23 PM   #3
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The on demand water heater is more efficient than the kind that heats up a tank of water. They claim they save up to 75% on energy compared to standard water heaters.

But they are a lot more expensive to buy.
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Old 02-18-2010, 01:22 PM   #4
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I find my LP efficiency is greatly increased when I connect my water heater to shore power.

Pat
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Old 02-18-2010, 02:22 PM   #5
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No RVer I've talked with has claimed the electric element in a 6 gal water heater is as fast as gas for heating the water, and for our house (the former one, sticks and bricks) the gas water heater was waaay faster recovery rate than electric.

Jammer, great way to simply break down the break point between propane and electric. Thanks for showing this, makes it easy to remember and use,

Jim
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Old 02-18-2010, 03:47 PM   #6
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There is no way an electric element,has the recovery rate of a gas heater.Been there,done that.
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Old 02-18-2010, 05:34 PM   #7
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Quote:
Originally Posted by Ganaraska View Post
The on demand water heater is more efficient than the kind that heats up a tank of water. They claim they save up to 75% on energy compared to standard water heaters.

But they are a lot more expensive to buy.
It depends but a 75% savings would be extremely rare.

Rv water heaters are small and in order to keep the size down some efficiency must be given up. So I use 75% for efficiency. A typical residential gas water heater would be in the 80-85% range. These are for efficiency of combustion and heat transfer and don't consider heat loss through the tank walls.

Most of the tankless units are also in the 80-85% range. To go above that they have to be condensing and while I've seen condensing boilers (have one in my house) I've never seen a condensing tankless water heater. Maybe they're out there.

If you use a lot of hot water it's the combustion and heat transfer efficiency that matters most. If you use very little hot water the amount of heat lost through the jacket starts to matter more. The efficiency benefit of tankless heaters comes from the absence of any heat loss while the unit is just sitting there.

So if you have a test where you compare a tankless water heater to a typical 40 gallon residential gas water heater, and your test involves using 10 gallons of hot water a day, sure the tankless unit is 75% more efficient (or whatever, make up a number and adjust the temperatures and the gallons a little and it will come out right). For most people that isn't real world, typically it's 15-20 gallons per day for each person in the household (stick house, including laundry and everything).
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Old 02-18-2010, 05:38 PM   #8
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There is no way an electric element,has the recovery rate of a gas heater.Been there,done that.
Dave
A 1500 watt heating element will deliver 1500 * 3.143 = around 4600 btu/h

A 12,000 btu/h burner at 75% efficiency will deliver 9,000 btu/h, about double.
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