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Conquest351
Conquest351 UltraDork
3/11/14 4:00 p.m.

Who has one? We have a 3 br 2 ba house and my wife and I along with our 18 yr old all take showers and baths (wife). Our water heater burned out the lower element and now makes weird noises and the wife wants to figure out a way to be more efficient. Who has any experience with these? Good? Bad? What do you know?

Tom_Spangler
Tom_Spangler Dork
3/11/14 4:01 p.m.

This thread is relevant to my interests.

kazoospec
kazoospec Dork
3/11/14 4:13 p.m.

My parents had one when I was a kid. The water was never hot. Warm/lukewarm at best. It didn't put out enough volume to have more than one showerhead running at a time and there wasn't a huge savings over a decent conventional waterheater. We hated it so much it was replaced within a year or two. That said, all that was approximately 30 years ago, so, like many other technologies, today's models could be entirely different.

SyntheticBlinkerFluid
SyntheticBlinkerFluid PowerDork
3/11/14 4:16 p.m.
Tom_Spangler wrote: This thread is relevant to my interests.

+1

Duke
Duke UltimaDork
3/11/14 4:17 p.m.

I have a Rennai gas-fired tankless. I bought it because it was the same price as replacing a 16-year-old tanker and installing a new stainless flue to make it code compliant. It supports a 4-bedroom, 2-bath house.

I like it a lot. It is NOT a huge gas savings over the old unit, though it is more efficient. It does save some gas. But the real deal is this - you never run out of hot water ever. 10, 20 people can take hot showers, back to back, no problem. It just keeps on trucking - no recovery time.

It does take small modifications to the way you use water. They are programmed to ignore small draws of hot water, because 9 times out of 10 when you are running a little (say in the sink, to wash your hands or rinse a plate) you don't expect hot water. Yet with the mixing lever typically in the middle, you're actually drawing from both supplies. So in order to prevent the water heater from firing up every time somebody touches a tap, it needs a certain volume being called for for a certain time before it lights up.

This means that sometimes, if you're running a modest amount of warm water, it will snooze on you. Or, like when you're loading the dishwasher, you need to keep the hot water running at a pretty good volume to keep the heater going. ordinarily you would turn it on and off with each dish, but you can't do that now. The flip side is that when you want just cold water, it's best to remember to move the lever to full cold rather than leaving it in the middle. When you want hot water, you have to run it at a pretty good clip for a short time to get its attention. If I turn the shower on in my 2nd floor bathroom, I have hot water in a little over a minute.

This is the main reason why the cost savings is not larger than it is. But it is still a savings.

Other than those items - and I think the "infinite hot showers" thing far outweighs the minor inconveniences - it's pretty much the same as a tanker.

Duke
Duke UltimaDork
3/11/14 4:19 p.m.

The older, under-sink type electric units can't make the volume, as Kazoo points out. But the Rennai will definitely put out. Whether you can do laundry without freezing someone in the shower depends on the piping layout, but the power is there to cover it.

Conquest351
Conquest351 UltraDork
3/11/14 4:21 p.m.

We do not have gas. This will be an electric only unit. Don't know if that helps.

Thanks Duke!!!

jimbbski
jimbbski HalfDork
3/11/14 4:41 p.m.

I saw a install of a water heater on TV that used electricity but also used a heat exchanger mounted to the top of the unit that drew heat out of the room and warmed the water to a higher temp then the room air. Sort of like a heat pump does. It works best if installed in a garage if you live in a warm part of the country but if you in a cold area then not so well unless it's in a heated part of the house.

stanger_missle
stanger_missle HalfDork
3/11/14 4:43 p.m.

Also, the water temp of the cold water plays a big part as well. If you live in a colder part of the country, your water will not get as hot as someone who lives in, say, Florida. Since the water doesn't sit in a tank, it only has a small amount of time to get heated as it passes through the unit.

In other words, the colder the water coming in the inlet, the cooler it will be coming out the outlet.

N Sperlo
N Sperlo MegaDork
3/11/14 4:48 p.m.
Duke wrote: *you never run out of hot water ever.*

Sold

aircooled
aircooled UltimaDork
3/11/14 5:17 p.m.

I have read they get clogged by hard water and have to be regularly flushed out. True?

Mazdax605
Mazdax605 SuperDork
3/11/14 6:23 p.m.

I hated the one we had in our boiler. We also have well water, that is very hard, and it wasn't very efficient. We have a boiler mate now, and in our first house we had one installed after dealing with the tankless. Tankless water heaters suck ass in my opinion.

SVreX
SVreX MegaDork
3/11/14 6:50 p.m.

What does "worth it" mean?

Most of the people I know who have them like them. But they were convinced before they bought them, and I think it is kind of a psychological appreciation.

Financially, I am convinced they rarely are cheaper (I've never seen a situation like Duke described where the install cost was similar).

It's kind of like people who buy hybrids. They are very happy with their cars after they buy them, and will tell you all about how they are saving money over their old 20 mpg car. But they never seem to notice that they traded a car that was paid for and took on a $30k car loan.

I've installed several dozen. A gas fired Rennai is a good unit, but installation costs are typically 3-4 times the cost of a tank unit. Electric units aren't worth the box they are packed in.

Incentives are often available.

stuart in mn
stuart in mn PowerDork
3/11/14 6:56 p.m.
Conquest351 wrote: We do not have gas. This will be an electric only unit. Don't know if that helps. Thanks Duke!!!

Electric tankless heaters that are big enough to handle a house with showers, clothes washers, etc. require a LOT of current - in the range of 80 to 140 amps, depending on size. Of course they are only using that power when you're running hot water so the overall cost isn't that bad, but it does mean you need to have at least a 200 amp service to the house, plus there is some heavy wiring required for connections to the water heater.

stuart in mn
stuart in mn PowerDork
3/11/14 6:57 p.m.
aircooled wrote: I have read they get clogged by hard water and have to be regularly flushed out. True?

They do tend to get clogged up with scale, so depending on how much you use it (and how hard your water is), they do need to be flushed out - maybe once a year.

petegossett
petegossett PowerDork
3/11/14 8:28 p.m.

I bought an AO Smith Vortex 50 galon tank heater. It's high-efficiency(it has a flue fan & is vented like a furnace), it can supply continuous hot water, and it's always on without the wait of a tankless unit. I think I paid $1700 shipped about 2 years ago.

I have a small Bosch tankless unit under the downstairs sink(separate water supply). The first one I installed was defective, the heating unit didn't shut off and it melted the CPVC pipe and spewed all over. The 2nd hasn't had any problems beyond the usual tankless issues mentioned above. Though it doesn't get much use.

aussiesmg
aussiesmg MegaDork
3/11/14 8:39 p.m.

I run one for the bathroom at my shop, it has worked fine for a couple of years, until someone who shall remain nameless. turned the room heater off during Winter and froze the unit, which promptly sprayed water everywhere out of the heat adjuster once it melted. To be fair, they also broke the toilet and only the Pex line saved the rest of the water lines.

However for the amount of water used at the shop it makes a lot of sense, the hot water never runs out, and I am not paying to heat a tank of water that doesn't get used for days or even weeks at a time.

If I did a full house I would use one smaller unit for each room which requires hot water. Then the use of the water will not affect someone in a shower elsewhere, as well as using less power to heat for one small area instead of pumping heated water from one end of the building to the other.

It has worked for me.

Ian F
Ian F UltimaDork
3/11/14 9:03 p.m.
stuart in mn wrote:
Conquest351 wrote: We do not have gas. This will be an electric only unit. Don't know if that helps. Thanks Duke!!!
Electric tankless heaters that are big enough to handle a house with showers, clothes washers, etc. require a LOT of current - in the range of 80 to 140 amps, depending on size. Of course they are only using that power when you're running hot water so the overall cost isn't that bad, but it does mean you need to have at least a 200 amp service to the house, plus there is some heavy wiring required for connections to the water heater.

Yep. Our plumbing dept loves to spec these little bastards, to which I'm usually ranting to them, "you want me to provide how much power under a bloody hand sink???" By the time you factor in the recovery rate and the delta-T (how much temperature rise the unit can do based on ambient incoming water temp), the power draw can be brutal.

codrus
codrus HalfDork
3/11/14 11:02 p.m.
stuart in mn wrote:
aircooled wrote: I have read they get clogged by hard water and have to be regularly flushed out. True?
They do tend to get clogged up with scale, so depending on how much you use it (and how hard your water is), they do need to be flushed out - maybe once a year.

That said, flushing it is easy, so long as it was installed with the proper service valves. Basically you put 5 gallons of vinegar in a bucket, turn the valves so that the heat exchange is disconnected, shut off the gas, and pump the vinegar through it for 20 minutes. I do it once a year (it's due now).

The plumber wanted $300 to do it, took me < $100 worth of parts.

As for the tankless unit itself, I like it. We installed it at the same time as repiping the house with copper, which reduced the installation labor. We also went with an outdoor unit (fine for California, not so good for the northeast) because that meant no special venting was required.

Infinite hot water, and it got me some extra space back in the garage.

pbkelley
pbkelley New Reader
3/12/14 7:33 a.m.

I have a Rennai - Natural Gas and I love it. As stated above it takes a little getting used to regarding the time to heat the water and how you wash dishes. My gas bill did drop. Just my wife and I in the house and our gas bill in the summer is always the minimum now. Installing it is a little more complicated, but doable. I have a split level house and moved the water heater out of the garage onto the back of the house. I was able to cap the lines in the garage and "t" into the lines under the kitchen. Wiring it was simple. Took about half a day including the trip to HD to get parts needed.

DaveEstey
DaveEstey UberDork
3/12/14 7:47 a.m.

I have a tankless water heater, but it runs through my oil-burning steam furnace to warm up. Never ending water that is as hot as hades and zero quirks.

None of that helps you though, unless you plan on converting your entire heating system.

Ian F
Ian F UltimaDork
3/12/14 8:41 a.m.
DaveEstey wrote: I have a tankless water heater, but it runs through my oil-burning steam furnace to warm up. Never ending water that is as hot as hades and zero quirks. None of that helps you though, unless you plan on converting your entire heating system.

My ex-g/f has a similar set-up. A System 3000 gas boiler for basebaord and radiators with a heat exchanger for domestic hot water. The system does have a 40 gallon hot water holding tank, but it essentially never runs out of hot water. When the effing boiler doesn't break.

16vCorey
16vCorey PowerDork
3/12/14 3:57 p.m.

I have a Eccotemp gas, and I really like it. It's probably not big enough to do multiple showers at once, although I can shower while doing laundry or running the dishwasher and just have to adjust the shower temp a little while they're filling. I have a one bath house so it's fine for what I've got.

I've never flushed it, but I do have a whole house filter and the water heater has a filter screen that I check about every 6 months.

Never running out of hot water is pretty awesome.

codrus
codrus HalfDork
3/12/14 4:15 p.m.
16vCorey wrote: I've never flushed it, but I do have a whole house filter and the water heater has a filter screen that I check about every 6 months.

It's not a flush, it's a descale. Unless you have a water softener, you'll get mineral deposits in the heat exchanger which will plug it up.

stumpmj
stumpmj Dork
3/13/14 8:51 a.m.

I have a friend who has an HVAC and plumbing business. He won't install them due to issues with scale build up and reliability in our area not to mention the pain involved with installing them. We do have pretty hard water in our area.

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