# Gas water heater capacity

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• posted on August 23, 2008, 8:17 pm

I need to replace my 50 Gal. gas water heater. I've been living alone in a house and never run out of hot water. I always take showers, never baths, and my overall hot water use is exceptionally low.
I'm wondering about two things. Would a 40 Gal. tank meet my needs and would I realize a noticeable savings by going with a smaller tank?
BTW, I rent the tank.
Thanks!
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<%-name%>
• posted on August 23, 2008, 8:40 pm

You mean by a 40 gallon gas heater? Or a 40 gallon electric heater? If comparing electric versus gas do a cost comparison of the two fuels, for your area. . As long as it provides sufficient hot water each time you use it is doubtful that you would save very much, if anything noticeabl;e by installing a smaller tank. the amount of heat lost from a well insulated tank/heater being very small. Note:
Also the heat 'lost' from the heater helps, in winter anyway, to warm the house!
Note. The difference in surface area of a 40 gallon compared to a 50 gallon tank will be approx. of the order of 22% (very roughly). So the slight difference in loss of heat from the hot water inside a well insulated tank to the ambient air temperature of whatever room in which it is installed will be very slight!
My electric company says that my hot water costs, typically, less than 20% of my total electricity bill. In my case as a single person less than that. So even if that could be reduced by one quarter the reduction in cost each month would hardly be significant. maybe 30 cents per day; at best?
My 0.02
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<%-name%>
• posted on August 23, 2008, 8:53 pm
"terry" wrote

Look another way. 30cents a day adds up to 30x30=9\$ a month. It may not be much, but it's a decent lunch a month when eating out, or 2 at many a fast food place.
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<%-name%>
• posted on August 23, 2008, 8:59 pm

That's right. If I could save \$9 a month and not notice any hot water shortage, I'd go for it.
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<%-name%>
• posted on August 23, 2008, 9:02 pm

i doubt the savings will be that much, ands check the first hour rating of the old and perspective new water heater. not all are the same
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<%-name%>
• posted on August 24, 2008, 2:42 am

most folks used 20 galon heaters decades back no problem. even with a family
if you are in a cheap electric area. pacific northwest, an instaneous water heater will save you a lot
I can get by with a 5 gal heater in my motor home ,, 40 is gross overkill imo
Phil scott
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<%-name%>
• posted on August 24, 2008, 7:09 pm
"phil scott" wrote

Probably. I just checked and we have a 40G gas unit. House of 3. We do have to time our showers/tub baths a bit but it is not hard. The dishwasher has to be accomodated for as well. Nominally need about 20 mins between bath/shower/dishwasher uses.
40G is plenty for one person. Ok for 3 with a little timing.
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<%-name%>
• posted on August 24, 2008, 7:07 pm
cshenk wrote:

Something definitely out of whack if a 40 g doesn't cut it for only three. Raised four kids and wouldn't be able to think of time it was an issue...
--
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<%-name%>
• posted on August 24, 2008, 7:46 pm
"dpb" wrote

Yes, and you are right. It's an older unit and was not maintained at *all* by the renters. I am pretty sure we are getting about 50% efficency out if it.
I dont expect anyone to really 'track' all any of our posts to add things up so I'll add I'm the one who was in Japan almost 7 years with house rented. I am pretty sure this unit was replaced while we were gone, about 6 years ago? I bet it has a coil problem of some sort.
We have to unpack the last of the boxes in the garage before we can just drain it and see what's up. Having only just repaired the 'sunroom' we have not yet repopulated all the stuff stored in the garage so this isnt an option to just drain it.
It is very possible the unit is about 7 years old now with zero maintenance. With regular maintenance, they nominally last 15 years. Not sure what you can expect with none at all though?
It is not impossible to think we might be getting about the efficency of a 20G unit just now? I only can see it is a 40G and a long shower (over 10 mins) means a reheat time of about 20.
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<%-name%>
• posted on August 23, 2008, 8:56 pm
On Sat, 23 Aug 2008 13:40:41 -0700 (PDT), terry

Yes I mean replacing my 50 gal. gas heater with a 40 gal. gas heater.
Wouldn't it cost more money to heat more water on an on-going basis? Just wondering.
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<%-name%>
• posted on August 24, 2008, 1:24 am

Minimal difference.
FWIW, we had a 40 gallon for our family of four in our old house and we never ran out of hot water. Showers, laundry, dishwasher, it kept up with our needs.
The savings to be had are the difference it takes in gas to keep 50 gallon versus 40 gallons at temperature. This is a direct ratio of the heat loss of the two tanks as the larger tank has more surface area. In either case, if you use 10 gallons of hot water it will be replaced by 10 gallons of cold water and on either sized tank it will cost the same to bring it up to temperature.
If you heat your house in the winter there will be no savings. The heat lost from the water through the tank and into the air is just the same as the heat from your furnace or boiler that would have to run longer, so, your savings may take place only half the year or so.
I'd replace it with the easiest solution. If the connections of the 50 gallon tank line up, it is an easy swap. If, however, you'd have to re-plumb for the smaller tank, you'd probably wipe out a year or two in savings.
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<%-name%>
• posted on August 24, 2008, 4:22 am
wrote:

Thanks Ed, this is good to know.

I was just thinking that a 50 gallon tank that needs to be kept at a certain hot temperature would require more gas than a 40 gallon tank.
I don't know how the tanks work, but I was assuming that the tank's complete contents are kept at a fixed temperature.
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<%-name%>
• posted on August 24, 2008, 4:40 am

Yes, they are. The greater the mass the more heat to be stored and the more heat given off during the down times. What you need to know is how often and how long the burner runs just to maintain the heat level. As I said, if that "lost" heat from the tank is helping to heat your house, there is no additional cost during heating season.
If you do downsize, under your circumstances even a 30 gallon would be OK. That is really a lot of hot water for showers or even a batch of laundry, especially since most can be done in cold water these days.
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<%-name%>
• posted on August 24, 2008, 5:48 am

As pointed out the cost of the slightly less heat leaking from the surface area of a 40 gallon tank as compared to that leaking from the surface pf a 50 gallon tank would be minimal.
Also that heat, if you heat your house during say the winter or longer (depending where you live) merely means that your furnace or other heating devices would operate slightly longer to make up for the heat 'not' coming from the hot water tank.
Personally thinking the the difference will be so slight that the most economical plan is just to slap in another heater with exactly the same dimensions and plumbing hook-ups.
Also as pointed out the cost of hot water is not, usually, one of the major ongoing household costs. Unless you consider that cost of gas will increase drastically?
Intensive discussion about the difference in cost of the amount of heat leaking (into the house itself) from keeping the difference of 10 gallons of hot water at a certain temperature seem rather pointless. Presumably the water heater/tank is insulated???
What we do is leave warm shower water and the occasional hot bath to cool down warming the air etc. in the bath room before drainuing it away. Of course because of moisture we run the bathroom fan while doing that which 'wastes' some warmed air to outside.
If you are really agonising about the overall cost of hot water and your hot water use is low; look at the cost of electricity versus gas in your area and the costs of installing a cheaper and smaller electric hot water heater. There will also be plumbing costs if you can't do it yourself. And then get rid of the gas connection, chimney or flue vent completely.
This discussion is getting far too complicated.
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<%-name%>
• posted on August 23, 2008, 10:50 pm

More exactly, (50/40)^(2/3) = 1.16, ie 50 would have 16% more surface.
Nick
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<%-name%>
• posted on August 23, 2008, 9:02 pm

Why rent, buy it its cheaper in the long run, you will save with a smaller tank. You will also save because the new tank wont have scale at the bottom. To save more shop and compare by EF energy factor, alot of cheap ones are still 50 EF
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<%-name%>
• posted on August 23, 2008, 11:27 pm
On Sat, 23 Aug 2008 14:02:54 -0700 (PDT), ransley

Well had I known I would be still be in the same house ten years ago, I would have bought a tank then.
If I buy a new tank now and move in a couple of years I think I would lose out on the deal. A move is a distinct possibility for me in the next few years.
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<%-name%>
• posted on August 23, 2008, 9:21 pm
RepairNovice wrote:

Check out the following:
http://www.nipsco.com/energyprograms/images/WaterHeaterInfoSheet.pdf
It's a rather indirect but valid way of guesstimating the annual savings a 1 person household would see in replacing an old water heater with a 40 gal vs a 50 gal.
So, assuming that the 40 and 50 gal heaters are equally efficient and adequate to your needs, you should save approx 20 therms per year with the 40 gal. Where I live, gas is running between \$1.25 and \$1.50 per therm, so that would be a \$25 to \$30 savings per year.
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<%-name%>
• posted on August 23, 2008, 11:27 pm
wrote:
Thanks Erma for this info!

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<%-name%>
• posted on August 24, 2008, 1:26 am

Well that depends. Where is the lost heat going? If it is going into the house and assisting the home heater there is really no savings at all during heating season so it may be half what is stated.