on demand water heaters

[dug]

Looking for opinions about on demand water heaters. I am considering one and like the efficiency advantages as well a their compact footprint.

Doing a little research revealed that people who own and use them either love or hate them. Lots of folks report frequent problems while others say they are the cats meow. Also they seem more tempremental, requiring a certain flow rate. My water comes from a gravity fed tank and I'm not sure how consistent the flow is, or how this might affect the performance of an on demand heater.

Also I am considering ditching the propane tank and going electric. Any specific problem with electric on demand heaters?

One thing I like about conventional tank heaters is that other then the tank eventually rotting out they always seem to work!

Thanks!

[MountainDon]

Electric on demand usually require a large capacity service entrance. They only use power when in use, but then they use a lot.  Ditto on gas/propane. They use a lot of gas when on so need a properly sized feed line. On a large on or in the ground tank there is no problem with supply volume; small portable cylinders are another thing though.

I betcha that a lot of the people who do not like their on demand did not plan things properly. Too small a heater that doesn't have the ability to raise the water temperature enough from the cold water from the well, for example. Or heaters that can only do one point of use at a time. Every good heater I've looked at gives the flow rate, heat rise, minimum water pressure, etc. Measure the temperature of the incoming water, now in winter is a good time. Flow rate can be measured with a jug and a clock. Pressure may require a gauge.

Drawing water from an elevated reservoir may not have enough pressure. The math is for every foot of elevation 0.43 PSI is supplied. I have our pressure regulator at home set to 35 PSI and that is a little slow at times. But it's easy on the fixtures, washer solenoid valves, etc.
They do not come on soon enough for folks who are used to using very low flows for some applications.

[glenn kangiser]

As Don mentioned , the electrics will use more power  by themselves than the entire house uses, while they are in use.

I installed the Bosch 1600 the other day for a customer.  It is an upgrade for my HX125.  

I found the 1600 to be a bit more complicated to set but once set it worked fine.  I instructed the customer to open the hot all of the way and rather than expecting super hot water to mix with cold plan on using more of the slightly less overheated water and not so much cold with it.  Turning a demand heater too high causes more scale.  Better to use it at a lower heat with less cold mixed with it.

Once you learn the differences in use patterns then it is satisfactory.

The customer had been using over a hundred dollars worth  of propane every few months keeping their tank style heater going for little reason - even when away.  This will eliminate waste as there is not a standing pilot to waste fuel or a tank of hot water to keep hot with the demand heater.

[Squirl]

Electric are generally recommended as point of use, like a faucet, not for a whole house.  The biggest complaint I see is that people complain their water doesn't get hot enough.  There are a few common culprits behind this.  The first most common culprit is that people don't make sure their intake line is large enough.  Many people have 1/2" lines running when the manufacturer calls for 3/4".  The second most common problem I have seen was that people were putting too much demand on the heater.  You have to read closely the GPM they are rated for when and look at the temperature rise.  Many people have a high flow shower head trying to use a 4 gpm water heater from a well.  This results in a cold shower.  Also a common complaint seems to be that they require a larger double wall chimney for a vent.  People don't realize how much heat they throw off to raise water from 33 degrees to 120 instantly.

I just had to replace a tank water heater last month, so I recently researched this.  I wish I could have gone with an on demand, but the house I was replacing it in couldn't take the setup.  I saw a critical article on them in consumer reports, but I think it was totally wrong on many assumptions and missed many points.  Tankless have a warrantee for 2-3 times longer than many tank water heaters.  They are all copper tubing heat exchangers.  There is no tank to rust.  The cost and damage of replacing a tank water heater every 6-10 years seems to get left out of most people's equations when calculating the cost/benefit of an on demand heater.  My father just had a tank style heater go.  It warped the whole floor of his house and it cost a few thousand dollars to fix.  In my next place I will be going tankless.

Also from an installation point of view, water tanks are HEAVY.  I think I read the on demand heaters are around 50 lbs.

[MountainDon]

There are readily available pans to be placed under a standard hot water storage tank. Many installation would require a sump pump to pump the water. Better than an indoor flood though.

Dug, since you are in the sunny SW have you thought of going the solar route? Dave Sparks uses a tank heater that was pre plumbed with internal coils for use with a liquid solar collector. I believe he says they only have to use the tank heater in the winter at times.  I'll see if I can find the make.

[MountainDon]

Here's the parent company,  A.O.Smith. On their website look for the AOSmith, American or State links. Maybe the other brand names offer them but a quick look did not find them.



DIY info
http://homepower.com/basics/hotwater/

[dug]

Sounds like I'm going to have to check my flow rate before I can really decide. Not so good because I have not run my water line yet, part of my bass ackwards approach to building.  I am thinking of replacing the gravity flow system for a pressure tank and that may eliminate any potential problems, but I don't know. There is 150 ft. between my well and house and I'm not sure if any sort of pressure drop may occur. I would greatly appreciate advice on this matter. Though I have no accurate measurement my best guestimate is that the water tank I have now is about 25 ft above our place and the pressure, while no geyser, has always seemed plenty adequate to me.

Any problems locating a tankless heater in a cabinet at floor level adjacent to an exterior wall?

Dug, since you are in the sunny SW have you thought of going the solar route?

I am definitely looking towards that. There is a girl helping me with my electric now that is trying to start up a business here installing solar hot water systems. She graciously offered to install a system for me at wholesale, about $1200.     I don't have the bucks right now but she said whenever I am ready she could tie it in with either a standard or on demand heater.

Thanks for the info!

[rwanders]

I have had really good performance from a Rennai propane tankless----my well water is at 38F and the tankless raises it to 120 and 3.7 gpm without much fuss. It is critical to determine your water temp and required gpm of hot water for your uses----that determines your btu requirement. My heater puts out 199,000 btu to do what it does so well. It is best to locate it on an outside wall if possible. The exhaust pipe is 5" in diameter and the shorter the better. I use a 100lb tank to supply it but that is based on my use of the cabin as a weekend or relatively short periods. A spare 100 lb tank is kept also for backup.

[davidj]

A few random thoughts on tankless water heaters...

According to http://www.engineeringtoolbox.com/pressure-units-converter-d_569.html, 25ft of water is about 11psi.  I'd guess that most on-demand heaters are probably spec'd for more than this.  This is certainly out of spec for a regular domestic water supply.

You probably want something between 130K BTU and 200K BTU.  Below 130K and you can't do a decent shower on a cool day, above 200K and things get expensive and the gas piping and tank size will become issues.  130K is certainly just a single fixture at a time and you'll probably want to stick with a 2gpm shower - this seems to be the rustic cabin approach.  200K BTU can do a couple of fixtures on a good day and is more of a regular small house size.  Whatever you do you need 3/4" for the low pressure gas lines, or bigger if you're 200K BTU and more than a few 10s of feet away.  Direct vent seems to be the way to go if you want the heater anywhere but a very well vented closet in the kitchen or main room.

Stainless steel venting can get seriously expensive.  With my 200K BTU Takagi I went up 2ft, 2 x 90 degrees and then another 10' or so horizontal ending in a concentric vent and I think I was approaching the $500 mark by the time I was done.  And the clearances are pretty huge for horizontal runs.  As far as outside termination, you have to be a reasonable horizontal distance from openings (detailed in e.g. the Takagi specs) and you also have to be a certain height above ground.  The Takagi install manual has a lot of details at http://www.takagi.com/download/product_manuals/T-K3.pdf and I think lots of the install details are code rather than brand-specific.  The unit only weighs 35lb or so.

Note there are some heaters with the different brands but the same hardware.  I think Bosch and Takagi are single-brand but Rheem and Paloma are the same company.  The 200K BTU Japanese brands (Takagi, Rinnai) seemed to have very similar form factors and clearances.  I went with z-vent venting, which is generic but with adapters for specific heaters.  So if I need to change my heater to a different brand in future I stand a chance of keeping the venting and using the same space without doing anything too funky to patch it in.

I spent hours sweating the details of the water heater installation - clearances, venting, supply lines - the inspector barely glanced at it!

[jdhen]

I have a steibel eltron tempra and couldn't be happier with the performance.   I had to run some pretty heavy gauge wire and 2- 60amp breakers but it does a great job.  With the recent deep freeze I actually had a thin layer of ice in the cistern so I know the water was pretty darn close to 32.  No problem getting the water to a nice warm temp for a shower.  I love being able to set the thermostat to the appropriate temperature and not having to add any cold to it.  In the summer I always shower with cold water and it's nice not having to keep water warming in a tank that I'll never use.

[considerations]

I have a Bosch 125 propane.  It professes to be non-electric in some of the ads, but I downloaded the manual before buying and there is a component that either plugs in or is hardwired to the electrical system that keeps the intakes from freezing.  It is installed on an outside wall, so it's "chimney" is built in.  A collection of sort of "fins" in a box on the top.

[Don_P]

I've only helped install a Takagi. It was on the windward wall so we opted for their damper kit that automatically closes if there is a backdraft, protecting the coils against a cold wind that might freeze them. Sounds like a similar concern to Considerations electric hookup.

[Yankeesouth]

Anyone ever use the small tankless water heaters?  Like Eccotemp L10.  I only need to heat a shower and sink. 

[Squirl]

No.  I didn't want to take a shower outside in winter.  Probably good for camping though.

" Outdoor Use ONLY!!! "

http://www.eccotemp.com/Instruction%20Manuals/L10-Manual%20Version1.0.pdf

This leads me to believe it puts out Carbon Monoxide and lots of it.  Be careful this can kill you really quickly in an enclosed space.

[MountainDon]

I suppose it could be mounted outside and plumbed through to the inside.

One thing I could not find in that link is the temperature rise per water flow rate. All it said was it could heat the water up to 150 F Missing is what the inlet water temp would have to be for that.

Might work with a low flow shower head depending on the inlet water temp.

[Squirl]

I noticed in one of your previous posts that you were looking at the Pittsburgh area craigslist advertisements.  You will have to worry about freezing if you mount this outside in Pittsburgh.

[Shawn B]

Dug,  If you have the space a regular 40 gallon tank with standing pilot will work out fine. Plus you will have hot water in power outages and won't have to hook up the generator. The cost of running a pilot each month is around the cost of a good triple-shot latte. The energy saving on tankless units are usually way overstated.  Keep in mind a standard 40 gallon water heater uses around 40K BTU's while running. Compare that to tankless units that usually start at around 199K BTU's while running. So for the amount of time that the water heaters are running, the tankless units use around 4X as much energy. The better more efficient units use electric for the combustion blower, etc. Sure the standard units cycle a few times during the day to keep the water in the tank hot, but these are much shorter cycles. Keep in mind some of the heat goes into the equation of heating the house anyways. The biggest advantage for tankless units is the smaller space requirements. Also the tankless units are very sensitive to hard water. Some MFG's want honor the warranty in some area's if the water is not filtered properly before going into the tank. Keep in mind that these units need to be "flushed" out every year or so with vinegar or some other safe cleaner.

[dug]

Shawn-

Still undecided but I am leaning slightly towards a tank heater at this point, taking into account flow rate restrictions, power supply and cost. The main drawback for me is the space consideration, I do have room for a tank heater but with small house every sq. ft. counts and the space could be perhaps better utilized.

I've been in the southwest part of the country for over 20 years and every place lived in thus far has had a tank heater in a separate enclosure outside the house and I am considering that also. Not as efficient I realize but I haven't had any problems with them freezing here. I have always set the thermostat to just slightly hotter than whoever in the household prefers their shower temp. the hottest, which is usually me so when I shower I have to just barely crack the cold to get the right temperature. Seems relatively thrifty this way, I don't understand why some people set them so hot.

Also I am pretty set on setting it up solar ASAP and the power considerations will be minimal after that.

[Rob_O]

One thing I could not find in that link is the temperature rise per water flow rate. All it said was it could heat the water up to 150 F Missing is what the inlet water temp would have to be for that.

Info on the eccotemp L10

    * Get hot water fast with the Eccotemp L10 water heater
    * Endless hot water at your cabin, summer cottage and more
    * Water heater has 10 liter capacity
    * Delivers up to 2.65 gallons per minute of hot water
    * Water ranges from 80-165 degrees F
    * Plenty of water for 2-3 hot water applications running at the same time
    * Two D cell battery ignition starts the flame only when water is running
    * No chance of overheating and makes it perfect for off grid or areas where you have limited electricity
    * Designed for a more permanent installation, the L10 comes with standard 1/2-inch NPT fittings
    * Ideal operating range is 25 to 80 PSI
    * Works great on modified water systems such as a 12 volt pump
    * Total dimensions are 28 inches tall (35 inches with rain cap) x 17 inches wide x 6.5 inches deep
    * Weighs about 18 pounds
    * 75,000 BTU
    * Includes stainless steel rain cap
    * Includes CSA regulator for use with standard 20-pound grill propane tank
    * Battery igniter means no electricity needed
    * Garden hose adapter included
    * 20-minute automatic safety shutoff timer

Temperature Rise:

    * 77 Degrees F: 1.6 GPM
    * 55 Degrees F: 2.2 GPM
    * 25 Degrees F: 2.55 GPM

[Shawn B]

Dug,  you might consider building a "Solar Breadbox Water Heater" to work with a standard tank type heater, either electric or gas.


http://www.youtube.com/watch?v=9IDcWbjm7W8

[duncanshannon]

Fwiw, when i contemplated this decision about 1.5 yrs ago, I opted for a traditional tank "this time" and in 6-9 years when it needs replacing THEN go for the tankless.  That is assuming they become more mainstream etc. etc.

[rwanders]

Anyone ever use the small tankless water heaters?  Like Eccotemp L10.  I only need to heat a shower and sink. 

A shower actually presents the highest usage rate for your water heater and most of us would be unhappy at less than 2.2 gpm flow.  If the Eccotemp L10 only produces a 55 degree temperature rise at 2.2, your input water temp would need to be about 55 or 60 degrees to perform adequately (if the manufacturer is accurate per their claim) I always assume they tend to be at least a little "generous" in their advertisements.

Undersizing a tankless is the source of most unhappy users-----saving a few bucks like that could result in an unhappy wife, and we all know what that can mean.

[archimedes]

Shawn-

Still undecided but I am leaning slightly towards a tank heater at this point, taking into account flow rate restrictions, power supply and cost. The main drawback for me is the space consideration, I do have room for a tank heater but with small house every sq. ft. counts and the space could be perhaps better utilized.

You could get a Lowboy tank water heater and probably fit it under the house.  You might have to dig out a few inches but it would probably fit fairly easily.  Lots of people do that here in FL.

I really don't see what the attraction is to tankless electric water heaters.  The prices I've seen around here are hard to justify compared to a tank heater.   It would take years and years to recoup the additional cost.  And that's assuming nothing goes wrong with it.  Would you know how to fix a tankless it if it broke?  A new heating element for a tank water heater is like $15 and an easy DIY project.

Tankless heaters have a reputation as being finicky,  and maybe that's all because of poor installation,  but I believe in K.I.S.S. (keep it simple stupid).  There is nothing simpler than a tank water heater - almost nothing to go wrong for years.  I've never had one that didn't last for well over a decade of trouble free use.

Add in the additional electrical requirements of a tankless and it's a slam dunk in my eyes.

[MountainDon]

Like rwanders stated, undersized heaters are probably the source of many (maybe most?) complaints.  The same can be said for PV systems; lack of sufficient storage and lack of sufficient PV modules makes more systems "fail" than anything else. Probably many other examples out there too. If the home work is done correctly tankless will work fine.

As a side note a tankless heater can also be used in a solar water heating system. The solar heats water in a storage tank that feeds the tankless. The tankless will fire up only enough to make up maybe 10 -20 degrees or more or less. In fact depending on sunshine, storage capacity and amount of use and so on, a tempering valve may be a good idea after the hot storage tank. A good solar heater can provide water that is hotter than what might be safe to use. The tempering valve mixes some cold into the hot line out of the tank. 

[davidj]

Anyone ever use the small tankless water heaters?  Like Eccotemp L10.  I only need to heat a shower and sink. 

We've got an L10 that we use as an outside shower and it's great for that use.  It just about gives a decent, if low-flow, shower if you're using it late Spring, Summer or Fall.  I don't think it quite gets to 2gpm, but it's close with maybe 38F groundwater.  You basically put the power on max and then turn the flow down until you get water that's hot enough.  It's a lot better than a bucket of cold water after you've been building all day but not exactly a substitute for a regular shower.  And it's very exciting on Summer afternoons when the hose has been in the sun - water comes out at something like 150F before the heater's even kicked in!

If I had something like a 10x14 Summer cabin I'd definitely bolt one on the outside and use it for the shower and sink.

I think I read somewhere that they're rated as indoor heaters in many parts of the World but aren't compliant with US regulations.  This would be consistent with their look and what I've seen in other countries.  They also cut out after something like 10 mins continuous use so you have to actively work to poison yourself with CO by repeatedly switching the tap off and on even if they were burning inefficiently.