Tankless water heaters

[David Nebenzahl]

On 11/11/2010 5:47 AM [e-mail] spake thus:

Hmm; interesting that in your replies to me above you were fairly pro-tankless in terms of energy savings, while you're much more cautious here.

I think what this really shows is that any energy savings due to tankless water heaters is pretty much on the margins. This isn't a bad thing from an energy-saving standpoint, of course: a therm saved is a therm saved (or a kilowatt). But it does indicate that calculating any kind of payback period for installing tankless heaters is problematic at best. This is where I think that some kind of curve showing usage patterns vs. fuel savings might be useful. I can accept the assertion that tankless heaters save energy overall; it's just not that apparent how much, exactly, they save or whether installing one is a good decision financially speaking.

[schmidtd]

It's fun to watch when some> [...]

I'm in the same boat.

My 14-year-old tank, perched precariously in the attic with (as it turns out) a clogged emergency drain, was in need of replacement. I was tired of re-lighting the pilot in 140F temperatures up there in the Southern US summer, and tired of worrying when it was going to rain down all of its hot goodness through my ceilings and walls when it finally failed. Plus, we're going to fix up some living space in the attic, and that thing was taking up way more space than it was entitled to.

We got a Rinnai, located it outside, upgraded the gas service from 1/2 pound to 2 pound, and all the trimmings. Worst case scenario, it would seem. It cost 2.5 grand, but I get about half of that back from rebates of various kinds. And it all happened in one day - nobody missed a shower. Everyone has adjusted to its behavior. I can't have short bursts of hot water any more (I used to shave that way - rinse out the razor every few strokes) so I've adjusted to filling the sink a little and swishing around the razor like my dad did. And now I get to threaten the kids in the shower with hitting the button to turn it off. Instant cold - very motivational.

I don't care if it costs more or less to heat the water. I don't care how many angels can dance on the head of a pin. I have a water heater for the next 10-15 years, it won't soak my walls when it fails, and I get some space back in my attic. Works for me.

[Oren]

Well said.

If a new build a tankless or three would be in the home. Retrofit -- that can be done also and work well.

Tankless heaters can last 25 years, have DIY replaceable parts, use a water turbine to spark the igniter (for gas), etc.

[Edward Reid]

Good point. I would have been eligible for the $1500 federal energy credit (because it's more efficient than the old one, nothing to do with being tankless), but I had already maxed out that credit.

Mine took a couple of days due to inspection scheduling, but the old HWH wasn't disconnected until the new one was ready to go, so only a couple of hours of outage.

Edward

[Douglas Johnson]

It's not that complicated. Tankless water heaters save in (maybe) two ways. The first way is standby losses. Tankless have none. Tanks' standby losses depend on how well insulated they are, but are constant with time, independent of usage. The savings I quoted in a previous message are almost all standby loss savings, we don't use a lot of hot water at that end of the house.

The second possible savings are any efficiency differences in actually heating water. I think most tankless are better than most tanks, but I haven't studied it recently. -- Doug

[David Nebenzahl]

On 11/11/2010 5:56 PM Douglas Johnson spake thus:

So it might be a toss-up between tankless heaters and those newfangled high-efficiency tank heaters that were mentioned in this thread ...

[ransley]

e

Actualy its less than 4 years, mine is the small 500$ unit with an extra 100$ exhaust blower, I put it in myself. It is a bit difficult to go over but in reality I saved 25$ a month because I went from electric tank to Ng, but electric costs have to be converted as they were about 30% higher per btu then. The electric tank was a 5 years old, well insulated with foam and a blanket so I consider it a good effecient unit. My gas went up in summer about 4-5$ a month to about

15$, my electric down 30 a month without ac running, a savings of 25 a month or 300 a year. But considering electric was maybe 30-40% higher per btu a 15$ a month comparison is better to Ng and that is a 180 a year or 720 over 4 years and I give myself something for the install. But I cut usage, insulated pipes so I think 4 years is a fair guess. But if you pay 1100 for a unit and 500 for an instal its a different game. So you see it isnt easy running the payback numbers and doing it right, but its saving me alot. Look at it this way, the only difference in EF rating from tank to tankless is standby loss. EF testing is standardised. Tankless go 93-96 EF is condensing and 83-86 non condensing. Tank start at 55-60 EF and go to about 82-83 EF. The only difference is standby loss which is about 15 %. So 15%

[ransley]

e

I hit send by accident, a 15% savings should be guarnteed. But if your Ng tank is is old it could be easily double, my 20 yr old tank I took out at a different location had 13" of scale in the bottom, 13" of small rocks reducing the tanks efficency. So there is more to consider. For a house I would do it again, for an apt building I went with a AO Cyclone, a condensing tank.

[hallerb]

ote

tankless sludge up too and may require pro service. its best to make certain that a affordable qualified service tech is in your area..

travel can cost a fortune

[Steve B]

See question 9

[trader4]

I'm not pro-tankless or against them. My earlier posts were comments on your analysis that somehow because a tankless, which has a larger burner, uses a lot of gas during the periods it's actually heating water, that it becomes inefficient compared to a tank type if you use it frequently. Whther you use a small burner for a long time or a large one for a small amount of time, the only thing that counts is how much hot water you get out for a given gas input. I've seen nothing to suggest that tankless are inefficient if used frequently. Quite the contrary, that is an application that they are efficient at and also suited too, because the water supply is endless.

It seems just about everyone here agrees that the main energy savings of a tankless versus a high efficiency tank heater are in the standby losses. Whether you can save enough on energy to make the tankless install pay back in a reasonable period depends on the particulars of the actual situation. And also, other factors, like having unlimited hot water or not having to keep a tank hot for an application where hot water is needed only every 3 days, etc, can also play a role.

If you agree that the main difference is that the standby losses are eliminated, then you don't need a curve because it doesn't depend on the usage. It's roughly the standby loss, which is constant.

[Oren]

Have you seen a residential tankless heater "sludge up"? I haven't. Tankless heaters are DIY friendly as far as replacing parts as needed. One heater over 25 years beats the pants off or replacing four tank heaters during that time period.

You got that right. Think of the 4,000 stranded cruse ship passengers!

[Oren]

I've seen about 16 or so tankless installed over recent years. Plan ahead...( in the desert here)

Zoned: Master plus hall powder room get one (outside) install. The far wing on the house ( 3 BR, 3 Bath) segregates the curtain climbing children or guest so they get one outside installed unit.

The mutual location is the kitchen. One unit installed inside the garage covers the kitchen, laundry and garage.

No zones? Install the units in tandem. 1,2,3 side by side, work in tandem and fire the heat when demands call for the second heater. The third tandem -- extra heat.

Tandem installs are perfect in the garage, on the wall with each access for viewing and inspection. Also mount power exhaust vents through the block wall.

[hallerb]

in some areas water is highly corrosive and fills the bottom of regular tanks with sludge. what makes you believe that sort of problem cant happen to a tankless. they even sell kits to clean the heat exchangers.

newer tankless are much more complex than the older ones with computer sensors and boards. they may not last as long as earlier ones...so the

25 year life may not be realized on todays models. and check the warranties arent they 6 years? have you priced the parts sensors and boards?

[Oren]

What makes you think it can happen? I asked your first /

Umm, there is no tank for the collection point?

Just for you Bob. I repeat: : " Have you seen a residential tankless heater "sludge up"?"

YAWN

[Ala]

almost as bad as bangladesh

[Ala]

a massage might help

[hallerb]

its best people are warned before spending thousands, just to price the parts. and like i said the heat exchangers can corrode, which cuts efficency and heat capacity. dirty exchanger equals less water, or worse less water heated your nice warm shower is now cool:(

the proof of this problem? many tankless manufacturers sell heat exchanger cleaning kits.........

i have seen this

[hallerb]

yep a non working tankless will likely massage your wallet. $$$$:(:(:(

[Han]

Prof Wonmug wrote in news: [e-mail]:

Just a reminder: My parents' home had as long as I can remember a "geijser" in the bathroom to heat the water for the shower. Later, we got another one for the kitchen, so we didn't have to heat water in a kettle or big pan on the gas stove in order to wash dishes, or whatever. This was back in the time that there was a local "gasworks" that used coke (the stuff made from coal) and water to generate cooking gas. Evverything had to be changed when the town switched to natural gas.

This is a history of one of the brands that made "geijsers":