Water Heater Question


Would there be much difference in operating costs for a 40 gallon gas water heater vs. a 30 gallon ?
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Energy req'd=f(weight of the water)----So with all other things being equal, increasing the tank size by 33% (10/30), one would expect to see the operating cost go up by 33%. MLD
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No, not really. The cost of maintaining the thermal mass will go up a bit, but surface area for heat loss must be taken into consideration and it is not linear. The cost of taking say, 20 gallons of hot water out of the tank and replacing it with 20 gallons of cold water, is the same.
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tank. Bigger tank (more surface area), more heat loss, so as you noted, some increased cost associated with maintaining the same temperature. MLD
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Wrong. With storage tank heaters, the primary cost is usage, not heat loss from the tank. Given that volume increases much faster than surface area, given the same amount of use, you might see a slight increase in cost, but I'd bet it won't be noticable.
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Not really. It takes a little bit more to keep the thermal mass warm all the time, but you have more water to draw from when needed. The real cost is the energy needed to heat up the replacement water coming into the tank. Tanks are better insulated today than they were years ago. My 40 gallon tank can hold the water hot for a couple of days with no added heat if no hot water was used is used.
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desgnr wrote:

Depends on temp setting and how many users. Operating cost is a function of how many minutes per day that burner is lit. Living alone, I could probably get by with a 20 gallon. A house with 3 teenagers, even a 40 gallon is struggling to keep up. I'd go with a well-insulated 40 gallon, for resale value if nothing else, if you have multiple bedrooms. You burn a little more gas getting 40 gallons warm than 30, but it cycles less often if there are multiple users. To save money, turn the temp setting down to the lowest you feel safe with and can stand to shower with. (120 or so?)
-- aem sends...
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On Sun, 23 Aug 2009 09:39:54 -0400, aemeijers wrote:

I had a 40 gallon that I set at the temperature the pilot kept it at and had no problems with hot water. The pilot was all that was needed to keep it warm. Increased storage cost will only increase in a gas water heater if you want hotter water. Otherwise the cost to run the pilot light should be about the same no matter what the size of the water heater.
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If I was shopping for a water heater I would go to www.energystar.gov and compare all by EF, Energy Factor is their efficency rating.
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far better off with the larger tank.
Vertex tanks are very high efficency and now qualify for the federal 30% tax credit. Plus their recovery is awesome. Never run out of hot water:)
although vertex tanks do cost more.
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Since our fairly well insulated (as from the factory) ELECTRIC hot water tank, in our slightly cooler basement loses heat so slowly that the water is still tepid after being away for a couple of weeks with it completely shut off (Yes that surprised us too!); opinion here is that heat loss from the tank itself or because a larger hot water tank/ heater be installed is almost insignificant.
After all;even a heater holding twice the amaount of hot water does not have 'twice' the surface area from which to lose heat!
e.g. Volume for a 'round' tank = circular area times height! and twice volume = say, twice circular area times same height. Since area = pi x r squared; the r squared would only have to double for the tank volume , or in other words the ' r ' (unsquared, would only have to increase by 1.4 times. And consequently the outside heat losing surface, of a tank holding twice the volume would only increase 1.4 times. So one could argue that, for that small difference, a bigger tank might be more efficient: in not losing static heat?
What does cost the money is to actually heat the water, by some 100 degrees F from typical ground water temperature of say 50 deg. F to perhaps 150 deg. F. Note 1. After that how much hot water is used or wasted etc.?
Gas (except expensive bottled propane) not available here so have never used gas hot water heater. Understand the advantage is that piped-in gas is a relatively cheaper fuel and/or the 'recovery rate of a gas powered hot water heater can be faster? Whether that in itself leads to more usage depends on the habits of the occupants/users.
Note 1: Some health departments call for, or recommend at least 160 deg. F for sanitary/safe dish washing! Whereas to prevent, say children from scalding themselves nothing higher than 120 deg. F is recommended!
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On Sun, 23 Aug 2009 12:18:37 -0700 (PDT), stan

Less then 120 degrees is a risk. They did this at the Ohio State University (to reduce energy usage) and it made several thousand students sick due to pathogen growth.
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all water heaters should have a energy guide label with yearly operating costs on label.
for me cost of hot water isnt nearly as important as comfort and convenience which is why I upgraded to a 50 gallon 75,000 BTU water heater, from my old 30 gallon 29,000 BTU unit/ this more than doubled the amount of hot water available. we rarely run out. money well spent
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Yes, no, definitely, and maybe.
It depends on the temperature it's set on. It also depends on the demand. If the 30 was marginal in providing hot water usage, the 40 will work less. Yes, it will take the same amount of energy to heat up the same amount of water, but from the same starting point. If the 40 has some warm water left, the starting temperature is going to be more than if cold water from the pipe is heated.
IMHO, the 40 wouldn't have to work as hard, but then there are the issues of heat loss during periods of nonuse. So, wrap it good, and whatever you get is whatever you get.
Steve
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a larger tank will likely have a longer life, since the thermal shock will be less.
the fewer cold to hot the better
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wrote:

Not sure, but I would say the one with thicker insulation and lower ef value will probably have the lower operating cost. Where I live it costs 2X as much to heat water with electricity than with natural gas--of course that can change but it hasn't in the last 20 years.
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The burner comes on only when the water cools down enough to cool the sensor. That's because of
1) use of hot water by opening a faucet 2) heat loss through the walls of the tank 3) heat loss up the chimney
The difference between heat loss of a 30 or 40 is minimal. The 40 is cheaper to buy and install, since it's a more common size. I'd go with the 40.
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