It’s time for a new electric water heater. Should I just replace the one I have or go to the trouble and expense of putting in one of those instant water heaters?

I’m kind of leaning toward an instant water heater because I’ll probably live here until I’m carried out feet first so long term savings are a priority.

Instant, no question.

One question, why electric?

We're definitely going for a (gas fired) instant heater once our existing (gas fired) tank dies.

But one unknown for us, is how much noise do these things produce when operating? Anyone know?

Our main motivation for going tankless is that our current tank unit is in a very suboptimal location, a good 15' from the nearest hot water outlet tap. Which means lots of wasted water as we wait for the warm stuff to arrive.

There's a much better location to put the heater, within 5' or so of all but one (the laundry) hot water tap here, but that new location is too small/cramped for a full tank.

Thus the real motivation for tankless in this situation, though the energy (and planet) savings are also a strong consideration.

Cheers

There is no gas service where I live (way out in the sticks). The idea of a propane tank and all trouble that goes with it is just not what I want.

Assuming these are essentially the same things as are sold in the UK as "combi boilers" (to which Wikipedia says yes), they're nearly silent. You can hear a slight, low-pitched whirring from the pump and maybe a low hiss when the burners come on, but if anything the sound is quite restful. (And of course you hear the pump with any central heating system, it's no louder with a combi system.)

Peter

One thing to consider with 'instant' heaters is the max hot water flow rate. ie ambient +X degC litres/minute.

The main problem is that to run a decent shower or fill a bath in a reasonable time you need many kW of heat to be transferred into the flowing water to raise the temperature. In the UK you'll typically be limited to about 3kW for an electric unit.

In the winter this equates to a lukewarm trickle from the shower

Gas of course avoids this problem and some 'instant' heaters and combi-boilers actually have very well insulated tanks built in - not as big as your traditional tank but enough to smooth out delivery. Also, IIRC, look up plate heat-exchangers; I think they provide a very compact way of heating flowing water.

Oh, FWIW I understand that washing machines are better served by a cold water feed.

The logic goes that they use so little water in real terms that by the time the pipe run has been flushed and some hot water trickles in then the tub is full and you just have a hot pipe run. Additionally they now run at much lower temps. All told it makes sense to just use a cold fill and let the internal heater warm it up.

That logic may be different in the US where washing machines are usually connected to 120V circuits.

Also, you can install instant water heaters inside, so the ambient temperature should be reasonably high. I would imagine that electric ones would have a 220V circuit for them.

Great tips and advice, thanks!


That would apply around the world, except for USA/Canada where most of us use inferior water hog top-loaders. With those, the hot water has plenty of time to arrive and give a good hot/warm cycle.

Cheers

Yeah, that sounds familiar -- lukewarm (not hot) showers have been the norm at just about all of the B&Bs we've visited in England and Europe.

Those are also the source of my question about noise -- there's quite a loud low-freq buzz from something when we're shivering in those showers!

Cheers

If the buzz comes from nearby, that's a pump in the shower -- a so-called "power shower". Like computer fans, small pumps are noisier than big ones. (My shower screams like a turbine.)

It's possibly also to do with the fact a power shower pumps "new" water the whole time -- unlike a heating pump which pumps the same water round and round a closed system -- which means that it's more susceptible to limescale and other corrosion or deposition, causing noisy operation.

Some power showers are also heaters, but most just pressurise hot water from a tank system. (You can't have a non-heater power shower with a combi boiler, because you'd be pumping mains pressure, but conversely you don't need a power shower with a combi boiler, because the hot water is already at mains pressure.)

Peter

Our heater is a Rinnai that has a coaxial vent duct and forced fan cooling. It makes a little bit of noise, but nothing you would hear unless you're right next to it.

It's way quieter than the old tank heater, which sounded like a large popcorn maker.

When I started working from home, I found the tank heater was firing up about three times in two hours, heating water that no one was using. It was also down to about 10 minutes of hot water, so it was really just heating calcium deposits.

Our first instant heater was one I smuggled in from Taiwan. It's a really simple thing, with one big knob to adjust the fire. I could easily boil water in the pipes. Initally I thought that if I was mixing in cold water at the tap, that I was wasting heat, but I found that the heater gets way more efficient the slower the flow, so we ended up setting the heat to near boiling and mixing in cold to get the desired temp. The flame setting was quite low doing this.

That heater lasted about five years (it was only $200) and I had to replace it with a locally available unit, so I got the Rinnai. This being the USA, with litigation always on the minds of manufacturers, so the Rinnai worked differently. It's got an electronically regulated temperature output capable of only 140f max, so we set it to 130f and leave it there. It uses a much larger flame than did the Taiwan one (Sakura), so it must be far less efficient. It's also way more complicated, but it's also a "set and forget" device. With the Sakura, we had to remember to adjust it for shower, dishes, laundry, etc... I think the Taiwan water devices must all have about the same flow, but that's not the case here.

If I was running off a propane tank, I would definitely want the Sakura type.

I also found that hard water was a big problem for this kind of heater. I ended up having to put a water softener in to keep the heater clear. What I did is install it upstream of the heater only, so my cold water is not softened. I find this is a great arrangement.

What would be a good test for this? Do you lose pressure?

I have a Rheem RTG-53PVN (made by Paloma) natural gas unit. It was put in about a year ago and I can't detect any difference in pressure one year later. I don't have any buildup around the shower heads, so I guess my water supply may not be very hard.

I paid about $670 for my unit and I was able to get $300 back in the form of a federal tax credit. That seemed like a total win until I realized the price of the 3" stainless steel exhaust pipe this particular model called for. The pipe actually ended up costing more than $700! Luckily, a friend and I were able to install the whole thing successfully ourselves.

The electronic temperature control on my unit is capped at 120ºF. There is a way to modify the controller to allow up to 140ºF in case you live in a high-altitude area. I was planning on doing that, but I find that 120ºF is WAY more than enough heat. I don't think I could stand more than a few seconds under that kind of heat.

The model I have is very quiet. You do hear some sort of motorized noise if you're showering in the room that has the heater on the other side of the wall. It's not very loud or annoying at all.

Overall, I think the tankless heater was one of the best things I've done to this house. Because I live alone, constantly heating about 50 gallons of water seemed very wasteful. Towards the end of the traditional heater's life, it was only good for about 10 minutes anyway.

That's what I found, the heat exchanger would clog up. I used a sump pump in a bucket with CLR in it to clean it up, but I found I was doing that every two months. With the softener in line, I've never had to do it again.

At my house, you can see the deposits on every tap and shower head, so it's pretty clear what the problem was.

Your water company probably publishes what's in the water. As I recall, all of NY has good water.

My Rinnai was $800 with the $300 tax rebate, including the coax stainless duct.

What I love about the Rinnai is that it never shuts off. You can take a 4 hour hot shower if you want. The Sakura would turn off every 20 minutes, so I'd have to shut off the shower to restart it.

I find that 125 degrees is minimum for me. When it's cold out I'd crank it up to 130.

I didn't even think of that thanks. I know they use a lot of electric when running so I figured the water temperature wasn't an issue.

Hopefully the manufactures list the "X" heating factor in your equation so I can tell what I'll get.

The house is wired for 200 amps. I'll have to do some adding to see if I'll be popping breakers.

You could get a HUGE propane tank and have it filled on a regular basis by the propane service people. It would probably still be cheaper than electric. And the water would be hotter. And you'd have a bigger selection of heaters to choose from.

If anyone has a need for a significant amount of hot water on demand, a number of heater models allow fitting in series. You can provide water to an entire apartment complex using the right on-demand heaters.

Okay, looking into this for real now.

Who else has an instant/tankless water heater, and what works and doesn't work well on it?

Brands, features ?

thanks.

I just moved into a house which has an on-demand water heater. It is powered with natural gas just like our furnace is.

I don't have a brand name for the one we've got, but it works fabulously. It doesn't save us any time getting the hot water from the garage to the shower, but when the hot water does reach the shower, its temperature is very consistent, even when other taps in the house are being used. I can safely shower while a laundry load is being run, for example.

Its noise level is noticeable, but since it's mounted in the garage next to the furnace, it's not a factor for us. In terms of volume, I'd say the on-demand system is louder than a conventional gas hot water tank would be while heating the water, but it's significantly quieter than a furnace.

The top brands are probably Bosch and Takagi. I've also heard good things about the Paloma brand Rob mentioned way back.

That likely has a lot more to do with your new house having a "modern"* pressure-balanced shower valve than anything to do with your hot water heater.

* Where "modern" means "within the last 25 years".

Tony's washing machine may also be relying more (mostly) on its own built-in heater if so equipped. My washing machine doesn't even have a hot-water connection, using only the cold and doing all the heating itself.

Bosch apparently doesn't have a great reputation for these, but Takagi does, and so does Noritz. I was originally looking at a Navien CR210A -- perfect for our setup here -- but after a bit of googling those appear to be crap at present. Maybe in a year or two when they mature.

But meanwhile, if Tony could perhaps read the brand/model of the one on the garage for us..

And anyone else?

Thanks

I don't have one, but I've only ever heard good things about Rinnai.

My workplace has on-demand hot water. Whenever someone uses it, it kicks on the UPS of my nearby computer. Those things must take some serious power.

I'm planning to buy an "indirect water heater" for home; a hot water storage tank. My oil furnace will heat the stored water when its temp drops below a set point. That way, I'll always have hot water waiting for me and won't start the furnace "on demand" when its tiny reserve of hot water is used. Also, the furnace doesn't have to maintain such high temp to be ready on demand, saving oil.