Tankless Electric Hot water heater ?

IMO tankless electric are not a good technology...pricey, not great water temp control, etc. The 'advantage' of tankless is low standby loss, which is moot for electric....without a flue, electric tanks can be very well insulated....look at energy factor EF, which gives the ratio of delivered BTUs to input BTUs in normal use....numbers for nice units (e.g. marathons) are 0.90 (i.e. only 10% standby loss). IF you have the space for it (like a large unfinished basement or attached garage) then heat pump water heaters are worth a look. I replaced my oil fired DHW with a 'Voltex' HPWH with an EF = 2.3 (i.e. it uses only 40% as much energy as a conventional electric tank). It cost $2000 for the unit, but saves me >$1000 per year vs oil.

First off, all electric resistance heaters are 100% efficient at converting watts into heat. You are not choosing an inefficient heating fuel but you may be choosing an expensive fuel. Depending on your area, electricity can be cheaper than oil or propane.

I, like woodgeek, am not sold on the whole tankless rage. The only benefit I can see is a space savings in a tight location. Plenty of drawbacks like sensitivity to imperfect water, high cost, complicated, and not as dependable.

As far as time for hot water to reach the fixture, it is exactly the same as a tank heater. There is a reason they call them instant. You still have to purge the plumbing of the cooled water before the heated water arrives.

The benefit of multiple smaller heaters is a shorter run to each fixture which can save you money by not wasting long lines of plumbing full of hot water. The drawback is reconfiguring your plumbing, several circuit breakers, high amperage circuits, and several units will be more expensive than a single large one. Unless you have a big split in your hot plumbing like a remote bathroom then I would stick to a single large one.

So I would recommend a standard electric tank heater. If you must go tankless and electric then a single big one in the same location as your tank would be.

Been there. Electric tankless was the first tech I considered too. Then I thought solar DHW. Then I thought conventional electric (marathon). Then I thought marthon + airtap. Then I settled on an all in one HPWH (Voltex). There is a lot of discussion of this tech in the Green Room if you search.

The good news is that there is an opportunity to save considerable cash. The bad news is that pretty much any tech will show a decent payback relative to oil. You don't need to find a cheaper method of heating DHW, they all are. You need to find the one that fits your budget, serves your needs, and hopefully is near the cheapest 'cost of ownership' (install + 5 yr operating) end of the spectrum.

One thing that helped me was to realize the low efficiency of oil for DHW. Maybe 20-30% of the oil BTUs actually came out as hot water, the rest went up the flue and into the boiler room (and doubled my AC bill in the summer). If you have a cold start boiler on your indirect you might be doing a little better (50%?), but probably you are in a similar place. So, most expensive fuel at 20% eff worked out to >$1000/yr just for DHW for me.

In VERY round numbers, conventional elec DHW (get a tank with 2" of foam, which will soon be standard on all tanks) runs ~3000kWh and ~$500/yr for a family w/kids with typical usage. Compare that to your summertime oil usage. I opted for an 80 gal HPWH that costs an extra $1-1.5k, but cuts the usage in more than half and my DHW costs <$200/yr.

Another advantage of tanks....hot (short) showers during power outages.

One big disadvantage of tankless (electric or gas) is that if your water is hard, they will scale up quickly, and there could be a lot of maintenance or a shorter life associated with that. You also have to have a 240V high amperage circuit for each tankless unit, and this can increase your cost of install.

A typical whole house electric tankless will require somewhere around 140 amps.

i had one put in 3 years ago.

http://www.stiebel-eltron-usa.com/

i am happy with it. it replaced a very old electric tank model. running the electric wires and the setup was expensive but in Long Island electric is very expensive too, and that is the only option we have other than oil or propane. gas lines have not reached my side of the neighborhood yet.

anyway, if i had to do over, i would buy an electric tank. just because the new models look really nice and efficient, and i would not have incurred the electric install expense.

but now that i have the setup, i will continue with the tankless, unless it really begins to crap out in the next few years.

Retired Guy said:

A typical whole house electric tankless will require somewhere around 140 amps.

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Very high amp appliances but, the ones I have seen, use more than one circuit so you are dealing with regular romex like 6/3 and since the materials are free the cost of the electrical work is zero. I imagine a basement with a stout panel and the water heater close by, it would be no sweat to add in a couple big circuits. For example, I used 3 feet of scrap 6/3 romex to add a 50 amp welder plug right next to my subpanel in the shop. Big circuit but the biggest cost was the plug.

glenc0322 said:

Did you have a whole house unit installed ? and if so how do you like it? How many bathrooms and sinks? and did you also use it for your washing machine? thanks

Glen

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Sorry, should have answered these basics first. It is a whole house unit installed in the basement. 2.5 bathrooms, 1 kitchen, washer and dryer in the basement. Handles them all with no issues. I have opened hot water at two faucets at the same time and no issues. The temp control is easy and the hot water stays that temperature and does not fluctuate. You just have to get the correct unit for the foreseen use and climate in your area, and then go a little bigger in case.

For disclosure, the original unit stopped working in the first 3 months and the company sent a replacement no charge. However the plumber charged me another $100 to swap the units. It was an electronics problem, which I image can happen with the new tank units too as they have more electronics.

Look them up on Amazon.com, you find plenty of customer reviews on them.

I have to say, I just recently started thinking of the effects of mineral accumulation in the pipes inside. Not sure how it handles them as only years will tell. But there is no flush valve for maintenance.

Good luck

woodgeek - I live in CT. You think HPWH can work in NE climate? Would need to put it in my basement.

Currently have oil burner for DHW.

Maybe all tankless do not have this issue, but one I installed for our kitchen water supply had this defect: turn on hot water, tankless quickly supplied, turn off hot water briefly, tankless reached shutoff point, turn hot water back on, a quick blast of very hot water, then cold water which then activated the tankless, hot water then again supplied, repeat.

Point is that in the kitchen we turn on/off hot water a lot to save water. Tankless did not work in this situation. Would work OK if hot water left on, then left off for long enough for water in the tankless to cool down.

slate said:

woodgeek - I live in CT. You think HPWH can work in NE climate? Would need to put it in my basement.
Currently have oil burner for DHW.

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Is your boiler ok with being shut down for long periods (i.e. the summer)? The major savings on any new DHW heater will be from reduced standby loss on the boiler. But many (cast iron) boiler were not made to sit idle cold. This is the biggest issue if you decide to go for either electric conventional or HPWH.

There is a lot of information out there that discusses 'heat stealing' by a HPWH as an issue in northern (heating) climes. In practice, if you are putting it in a (large) semi-conditioned space like a basement or an attached garage, then it will drop the temp in that space 1-2°F, and heat stealing from the conditioned space is not that significant.

If you are numerically inclined, the simple explanation is that about half of the BTUs in the output water come from the grid (powering the compressor) and the other half come (worst case--in conditioned space) from your central heat (in the winter). If your space heating BTUs cost that same as electric resistance (and oil is close), then in the winter the HPWH and conventional cost the same to operate. You would still save 50% in the summer.

Sorry about the complex answer...I'll boil it down.
--conventional elec DHW for a family costs $400-500/year. Compare that to your summer oil usage to see if you would save. Older boilers often run >1 gal oil/day, so over a summer that can add up.
--HPWH in semi-conditioned space >50°F, or conditioned space in a house with cheap BTUs (wood) will cut the number above in half, saving ~$200-250/yr relative to conventional elec.
--HPWH in a conditioned space with expensive oil heating will break even with conventional in the winter, and save 50% in the summer. So this case might only save $100/year net relative to conventional elec.

Also, it turned out half my AC bill in the summer was from the waste heat put off by the oil boiler...another $100-150 there if you shut it down. Previously, many times it would cool off outside, we'd open the windows and the house wouldn't cool off. I still cringe when I hear my neighbor's AC cranking when it is 65°F out for this reason.

To woodgeek,

Just reading about HPWH. I was considering a Solar DHW system with a tankless WH as cloudy/winter makeup. Was thinking Solar DHW using a HPWH might be a good way to go. Your Thoughts?

Thanks

We were in the same situation and chose to fit a Geyser HPWH in parallel with our oil water heater.
We kept the tank intact and used it as a storage tank for the Geyser.

The geyser is in our basement, which is fully in-ground.
The air temp down there does not get below 55 degF year round
We have run the Geyser as our primary source of DHW for about 2 years now.

We save 1 gallon of oil per day and increased our electric bill by $15 per month on a yearly average.


Our Geyser makes great gains in cost saving from April thru November.
It makes a huge difference in the summer where the hot air into the HPWH helps the efficiency and the dry air output helps lower the house A/C bill.
I've found that we are never worse off in winter, just a smaller gain.

If we have a housefull of guests, I turn on the oil water heater to help with water temperature recovery.
On very cold nights (circa 10 days/year), I do have the oil WH on a timer so that it heats water for the morning showers.
Otherwise the Geyser does it all.

I agree with Woodgeeks numbers in the post #16 above.
I actually think that he is being conservative as our numbers are better.

I can't comment on the electric tankless, but I did put in a natural gas tankless. The wife and I absolutely love it, never experienced a down side to it in the two years its been in. We were told if we run 4 or more appliances (shower, dishwasher, clothes washer and a sink for example) at the same time then the volume of water will drop to nothing. We haven't changed our lifestyle at all and never seen it drop. I suppose if you have 4 people showering in the morning all at once it might be an issue, but it works great for us, big thumbs up for tankless.

jrd1990zr1 said:

To woodgeek,

Just reading about HPWH. I was considering a Solar DHW system with a tankless WH as cloudy/winter makeup. Was thinking Solar DHW using a HPWH might be a good way to go. Your Thoughts?

Thanks

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Solar DHW + HPWH would have the lowest operating costs (if NG is not an option), but ties up a LOT of capital for making hot water. If you already have a HPWH and are spending $250 a year, putting in solar DHW system with a 60% solar fraction drops your annual bill to $100. But if a pro install solar system costs $10k (min), saving $150/yr, that is a 60 year (simple) payback!

The same comparison for an electric tank at $600/yr, versus a HPWH costing $250/yr...the HP saves you $350/yr, and costs ~$1000-1500 more than the conventional, for a 3-5 yr simple payback.

I have a neighbor who uses a solar DHW system as a preheater on his GE HPWH.
He's an engineer and self constructed the solar DHW system. Works well.

Physical size restraints on his property stopped him building a 100% Solar DHW system but his DHW numbers are in line with Woodgeeks in post #20.

We've had a Rinnai tankless for about ten years. It's saved us money because our propane is very expensive. It only cost $1700 to install it back then, and I think we reached payback after a year or two.

As far as time for hot water to reach the fixture, it is exactly the same as a tank heater.

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It takes a lot longer for the water at the tap to heat up, here's why: With a tank heater, the hot water in the tank is continuously diffusing into the pipes. So, with a tank, the water in the pipes is usually pretty hot. Of course you are spending money on keeping those pipes hot day and night.

This delay is the biggest disadvantage we see, but our water is cheap, and we are patient. Just checked, and at our kitchen sink it takes 16 seconds before the water stops being cold, and 27 seconds before it reaches full temp. For one of our showers it takes about 2 minutes IIRC.

I've insulated the pipes where they are accessible, and that helps if you used hot water recently.

Every year I flush the heater with a special procedure and vinegar.

The other day I was showering when the wife did some laundry, and the flow definitely decreased. But that hasn't happened much.

The unit requires about 4 watts of electricity, and won't work when the power's out, but I use an inverter and plug it into the truck so we can shower during outages.

Our propane usage went way down after the installation, but I also started using the furnace less.

Bottom line: I think it's saved us a lot of money, and would do it again.

WarmGuy said:

It takes a lot longer for the water at the tap to heat up, here's why: With a tank heater, the hot water in the tank is continuously diffusing into the pipes. So, with a tank, the water in the pipes is usually pretty hot. Of course you are spending money on keeping those pipes hot day and night.

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I don't believe this. Perhaps if your water heater is in a basement and you failed to install heat traps but my tank is on the same floor as the house and from the heater the pipes go down under the house and then back up to the points of use. I have never felt a warm hot water pipe unless it was being used. Further, when I wait for the hot water to arrive at my tap it switches from cold all at once and not some sort of mixed temperature followed by hot water.

Interesting theory but we would need to see more evidence.