Probably a 40 or 50 gallon, I dont think you need an 80 gal. I still think you would be better off with a propane heater, look at power vent heaters that dont need a chimney, they're about 95% efficient.

i would go with electric 50 or 80 gal.

Now why would 2 people need 80 gallons of hot water?

Electrics recover more slowly.
Dollars are up to you; you know best.
40 gallon water heaters are "bread and butter."
They are competitively priced due to high
contractor demand.
The further you stray from 40, whether up or
down, the higher the price.
Have not priced in last 8 years; technology
has changed; prices are up.

Rules still apply, but check prices.
...
Either:
1. Get 2 40-gallon water heaters and hook
them up in parallel. This means you have a "T"
in the incoming and outgoing water lines, and
that the pipes from the T to each water heater
are the same length. The T acts as a splitter.
2. Hook them up in series. Then the
first water heater does all the work and
the second acts as a storage tank.
...
If you are responsible, you and your wife
will not need more than 40 gallons. But
you must consider dishwasher, clothes washer,
shower and bath usage.
...
With a parallel hook-up, you can reduce
the load per heater. When one fails,
you can shut its water supply and continue to
use the other.

With a series, you strain the first WH
immensely, and you will have no immediate
recourse when it fails.
...
A main reason for early WH failure is
high heat. Heat causes corrosion of
the anode rod and tank, and sediment
build-up in the bottom of the tank.
The lower the heat, the longer the
life.
...
With 2 electric water heaters, you
have 4 heating elements, so you
speed up recovery time dramatically,
and you can do this at a lower heat
setting.
You have 2 anode rods, so you
reduce corrosion over time.

I take that back about anode rods; I can't say one way or the other.

Regarding "Now why would 2 people need 80 gallons of hot water?"...

If they have a whirlpool 40 gallons goes pretty quick.

Personally, I'd go w/ a minimum 50 gallon or larger. Actually, the actual water heater cost for a 80 gallon versus a 50 gallon is somewhat insignificant when you amortize it over 10 to 15 years & the annual operating costs are not a huge difference so I'd just replace the 80-gallon tank w/ an 80-gallon tank.

If you want to somewhat feel like you are making the right decision from an "enviromental" perspective split the difference & go w/ something in the range of 66 gallons.

25 years old? Not this time. You will be lucky to get 10 years. The difference is probably double to triple the operating costs between a 40 and an 80 gallon electric. HD sells a 40 for about $225. As I grew up, 20 gal. was considered the average for a family of 3 and sometimes 4. I will install a 40 for a 3 bdrm. house next week. It is a 2 hour job. This subject is not that complicated.

Check out Marathon water heaters. They're made quite differently from the HD variety and should last much longer. This is what we're installing in our new build.

Kevin

Here is a link that might be useful: Marathon Water Heaters

i agree. marathon water heaters are the best.they are kind of hard to find in some places though.

Go tankless! I'll never purchase a tank water heater again. I highly recommend the Rinnai tankless hot water heater. More expensive than tank models but pays for itself with energy savings. I purchased the Rinnai V2532W (propane gas) 2 1/2 years ago and I've never run out of hot water since. We can have 2 showers going at the same time with good water pressure. It only uses energy when you turn on the hot water faucet. Tankless has been around for decades in other countries. USA is just catching up.

Here is a link that might be useful: Forever Hot Water - Rinnai Tankless

Bob Brown, you continue to amaze me with your misinformation. Why would you make a statement like "The difference is probably double to triple the operating costs between a 40 and an 80 gallon electric."

If you had ever looked at the required Energy Guide labels on the water heaters you would know better.

If you go to:

http://waterheating.rheem.com/dealers/catalogRes_detail.asp?id=24

and pull up the PDF spec sheet you will find that their tall 40 gallon (83VR40-2) water heater has an average annual operating cost of $402. The tall 80 gallon (83VR80-2) water heater has an average annual operating cost of $411. That's a $9 difference not 2 or 3 times which would be $800 or $1,200.

While I think realistically it would be a little higher it is certainly not 2 to 3 times.

Re: "With 2 electric water heaters, you
have 4 heating elements, so you
speed up recovery time dramatically,
and you can do this at a lower heat
setting. "

this is only true if your electrical wiring supports running 2 water heaters at the same time. With a single water heater you have 2 heating elements but they are never both turned on at the same time. With 2 water heaters/4 elements & using the existing wiring to what was a single water heater, you still most likely (unless they oversized the original electrical wiring by a large amount) need to limit the 2 water heaters such that only 1 of the 4 is on at the same time.

The OP would most likely have to run a new 240V line to the location to support the 2 water heaters or they could wire the controls up between the 2 water heaters such that they never have more than 1 element turned on at the same time.

I think two 40's would use way more power than one 80, you have twice the tank surface area to lose heat through and when both are going you'll be using almost 10 Kw of power. Another option would be use one all the time and only torn on the second when company comes over, which is a pain. A single 50 gallon sounds like a better solution, unless of course you go gas or tankless. You already have propane available so why not look at tankless LP heaters.

You will need a couple of large solar collectors on your roof and a 135 gallon solar water heater and then two 30 gallon regular electric heaters zoned to differnet water use areas. Should be able to get it all setup for under 10k. Should have payoff of under 100 years. Hurry up if Al Gore is right we may have to swap over to water chillers in a few years though.

HereÂs what we did a few years back, and weÂre very happy with our choice. We installed an electric OSO stainless steel 62-gallon hot water tank. Water temp is 175ºf. Internal cold water mixing valve reduces output temp to 120ºf when there is a demand for hot water. This gives this 62-gallon tank the equivalent hot water reserve and output of a 90-gallon tank. WeÂve never run out of hot water. OSO has a 15-year guarantee; you have a problem with leakage, they replace the tank.

SR

Here is a link that might be useful: OSO Stainless Steel Hot Water Tanks

I actually thought about running a hot water "loop" up through my attic during the hot summer months, a simple parallel piping arrangement with isolation valves going up to a loop of copper in the hottest part of the attic and an insulated return pipe. I could build it for about $100, of course it would only supply hot water about 4 months a year and would need to be fully winterized in the fall.

for 2 I would say stay with at least a 50 gal electric. and about the split power rate thing I had that at my last house that was all electric. the off peak rate was 8pm to 8am and all day on weekends. the house had a time of day meter and the water heater was controled by a small box next to it that was wired to the meter. it had an overide so if you needed more water during peak time you could get more. If you bathe and do your washing in the mornings and eveinings mostly your fine the tank will store the water and it will be plenty to wash your hands or fill a sink with dish water. The problem is when more than one or two wants to shower outside of the off peak time when the heater is on or you want to do laundry. I had a 50 gal bradford-white with 3 in the house, I would always run out early in the evening when washing and all happened before 8pm. now I have gas, I love the way it recovers faster and no on/off-peak rates.

The cost of running 2 40-gallon water heaters is not found by adding one to the other. With 2, you have more of the benefits of the 80, yet not nearly the cost of a 40 in two separate houses. Two 40's together may even cost less to operate than the 80, depending on usage.