What size is your electric service? Most of those on demand need three 40 amp feeds. That's a lot of power and 6 spaces in your panel. If you don't have at least 200 amp service forget it.

Have you considered propane?

There are plusses and minuses to tankless heaters that you can find all over these boards and elsewhere.

Putting that aside, you need to look at the cost. You're spending $150/2 months for hot water. A tankless heater with similar capacity is likely to cost several thousand dollars to install, and will still cost money to run. Say you save 50% (which is not likely). That's $75/2 months or $400/year. That's at least 10 years before you break even (and I'm not even adjusting for present value).

Will you move in that time?

Will oil prices go down or electric prices up?

What is the current price of oil? If you're locked in at ahigh rate, it may be cheaper for you to break that contract than to get a tankless heater.

I highly recommend an electric on demand water heater over the one from the coil of your furnace. Your furnace still has to run to keep the temp up for the coil even when you aren't using it. Also, you can shut the furnace down for the summer.
I don't know what unit takes 3 -40a circuits or any costing several thousand dollars. Must be for a 2-family house or many hot water needs at once.
Anyhow,you can purchase a Titan Industries tankless electric for $250 & it should do the job for the 2 of you. You will need a 50amp breaker so you should have enough ampacity room for it in your panel. Of course if you can't DIY you will have to hire someone to install it, but still should keep it reasonable priced.......MrMike

Check out the spec sheet on these two heaters. On uses 80 (2x 40) amps the other uses 120(3x 40) amps.
Also check out this one. It ranges from 50 amps to 150 amps.

I don't know what unit takes 3 -40a circuits or any costing several thousand dollars.Mine is rated at 120a, has two 60a breakers in the house subpanel, and two sets of four ganged 40a breakers in a separate subpanel for the unit. This is a single-family house, 3BR, 2 full baths, 2 half baths (one is in the garage). The house was built 4 years ago by a developer, I don't know what the tankless cost. I vaguely recall that sales literature I saw later for the unit involved indicated $1,025 retail.

I've seen it run at full-capacity only during cold-snaps of near/below freezing temps that lasted a couple days which dropped the incoming water temp (well-water) pretty low, when I raised the set-point to 140°F for a specific hot-water task. Typically it runs as little as 7% of capacity to 66% or 70% ... but of course still needs a 120a circuit.

Hey thanks guys, "I guess I should have looked before I leaped" on this one. Those units take beau-coup power & would cost substantally more to install!
However, I can attest to this Titan as I have had it in my house, which has well water, for three years now without a hitch. I have it set at about 80%. There are just the 2 of us,like Aieger, and it fufills our needs with hot water for our showers, dishwasher, etc, & has saved us alot of money over using the furnace for the hot water. Note* I plumbed this in, so if there was a problem with the unit I could valve it out & valve the furnace back in, until I got it fixed or changed out.

You can no doubt save considerable amount of money by not using your oil furnace to heat your water. However, Electric tankless are generally not the way to go for full house water heating. The savings over an electric tank heater is only a few percent. Buy an electric tank heater.

THE SAVINGS OF AN ON DEMAND ELECTRIC WATER HEATER IS 50 TO 60% OVER A CONVENTIONAL ELECTRIC TANK HEATER. THEY ONLY USE ENERGY WHEN A HOT WATER DEVICE IS TURNED ON, WHILE AN ELECTRIC HOT WATER HEATER HAS TO KEEP UP THE TEMP OF THE WATER ALL THE TIME,WASTING ENERGY EVEN WHILE NOT BEING USED. TANKLESS HEATERS ARE THE ONLY WAY TO GO, WHETHER ELECTRIC OR GAS!!!

MrMarv,

Just because you type in all cap letters doesn't make it so. Please do just a little bit of research to support your claims. if you compare the power factors of electric tank water heaters to electric tankless water heaters you will see that there is only a three percent difference.

On gas, it's a different story. There is about a 35% or more reduction in gas usage. Depending on the cost of gas and installation, it can have a payback of about 5 years... which is okay, but not great.

I have done the math and I have a gas tankless.

if you compare the power factors of electric tank water heaters to electric tankless water heaters you will see that there is only a three percent difference.

This does not make sense from two points.

First power factor is a non issue in home power since POCO does not bill on power factor.
Second both units are pure resistive heat. Power factor should be 1.

joed,

Sorry, my mistake... intended to say energy factor, not power factor.

Thanks everyone for the great information. I have asked the hubs to study the input and all the suggestions and we will make a decision based on that. In the mean time, if anyone else wants to put in their 2 cents, we relish the info. Thanks /Abi

I don't know if such an animal still exists but some wood heaters/stoves had a water jacket incorporated, my mum and dad had a dedicated "chip heater" in their kitchen (this was, admittedly in New Zealand) that not only heated the water but the house as well.

Perhaps there's a pellet stove option with this, it might be worth considering.

Still looking for an answer on running a new loop onto the furnace for a cold start on demand hot water, vs. propane on demand hot water, in which I have to install it in my bathroom because we have no way to vent it out of the cellar.
I already have propane, the cost to install is within $100, though there is the Govt. tax break for the propane.
Which is more efficient?