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Sunday, December 31, 2006

Wishing I were in hot water [for a change]

Burst pipe repaired... water mopped up and water damage seems to be limited... phone/Internet cable temporarily mended (thanks Avi)... plumber due out today to look at hot water heater/tank.

I honestly don't have anything meaningful to offer this morning.  I do, however, have a few questions:

Does anyone out there have any experience with on-demand gas-fired water heaters?  If so, I'm specifically interested to know about the following:

1.  Savings (over traditional tank/electrical element system): big, small or a wash?

2.  Shabbat:  Is there a way to use hot/warm water on shabbat for washing dishes?

3.  Regulating output temperature:  I've heard that output temp. can vary based on demand (i.e. how much water is being used at any given moment).  Are there units that compensate for this and maintain constant output temperature?

4.  Any other reason I should/shouldn't consider one?

Thanks in advance for any and all information you would care to share.


Posted by David Bogner on December 31, 2006 | Permalink


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David, I've just had a condensing boiler fitted at the most enormous expense, and I wasn't expecting to have to do it. But having said that, I can already see it is going to save an enormous amount of energy.

It is on for a fraction of the time my previous boiler was on. I imagine that even with the huge sum it cost, it would pay for itself over ten years.
Or even half that time according to the chart attached to this page:


The issue is whether you would stay in your home that long.

In England, I'm using my boiler much more for heating than you would do in Israel. So maybe you would have to use a system for twice that long for it to pay for itself. But it will be 90% efficient rather than 60% efficient-- you will only pay for the heating of water you actually need to use hot, instead of having the boiler cycling to keep a water store hot. A good add on control system will help ensure absolute accuracy with temperature desired. You will save energy whatever the amount of water you use.

A downside is you can't use power showers with this kind of boiler.

I don't think it can be Shabbat proof because the whole idea of the thing is that it ignites only on demand. But you need to check that out with the Israeli organization that works on the technologies for Shabbat use.

In the UK, we are now compelled by law to fit boilers of this type--part of the national policy to cut energy use:


I'm very impressed by the extreme quietness of the new boiler and the sophistication of the control and switching options.

Posted by: Judy | Dec 31, 2006 1:54:01 PM

I don't know anything about the technical aspects, shabbat aspects etc but I can say having used one of these they are amazing. It is fantastic that you don't have to wait for your hot water, especially for you with a family of 5 it should make a big difference. And I have heard they are big energy savers. I know that on the list archives of the beit shemesh list there was a big discussion about these types of water heaters and the shabbat aspects etc - so you might find something useful there.

Posted by: Katherine | Dec 31, 2006 2:15:10 PM

shalom trepp...sorry i have not been online...we have a thing called a junkers 'yunkers'...amazing...works on a pilot light...only turns on when you turn on the hot water and never runs out...we don't keep the pilot light on all the time so when the dud shemesh is working we use that...i wouldn't hesitate to get one...when we were five at home it was a blessing...and now that we are two old farts and a college kid it is still a blessing...good luck and happy sylvester

Posted by: marallyn | Dec 31, 2006 3:12:14 PM

I'm a little confused - what's an "on demand" gas fired heater? What's the difference between a traditional hot water heater with a pilot light and the on-demand?

Just curious?

Posted by: jaime | Dec 31, 2006 5:23:48 PM

I don't have concrete answers, but keep in mind the maintenance of the solar/electric boiler. The container needs to be changed every 7-10 years, and the "koltim" (solar panels) and the heating unit every 2-4 years, in our experience. The gas needs virtually no maintenance.

Posted by: mother in israel | Dec 31, 2006 5:45:25 PM


On-demand units have no water storage. They heat the water as it passes through the unit. They are also called flash heaters.


I have experience with 3 kinds of flash heaters.

The first was the shower head heater in Brazil. Not good. At best it delivered a tepid shower. Flow rate determined the heat of the output.

The second was a propane-powered flash heater aboard the boat I lived on. It delivered scalding water on demand. It was a small unit, less than a square meter. I would think there must be something like it for those who live on the hard.

The last was an under-sink unit that was not truly on- demand but a small water heater-thermos. They come in a few sizes -- 1L, 2L, 3L, 4L. They deliver hot, hot water at the tap immediately and relieve the demand on the main unit.

Posted by: antares | Dec 31, 2006 6:57:06 PM

Mr. B-

I think we have a similar system here at the yeshiva. The one we have can be quite annoying; one must turn on the tap, then go out to the control panel and press a button or two, and wait for the water to get hot. Sometimes the heater is already activated, but it takes a few minutes before the hot water starts flowing again. Very annoying, and our system seems to waste a lot of water before anything hot comes out of the taps. Hope everything gets straightened out in the end.

Posted by: tnspr569 | Dec 31, 2006 7:30:13 PM

Hi Trep,

Thanks for running a great blog that I've really enjoyed!


Posted by: Maksim-Smelchak | Dec 31, 2006 8:46:13 PM

Just bought an apartment with Yunkers...for some reason it is only set up for heating. So far so good, but I hear it isn't cheap.

Posted by: Safranit | Dec 31, 2006 9:09:42 PM

All the best in 2007 beginning with your heater!

Posted by: The Misanthrope | Jan 1, 2007 2:14:13 AM

I have heard nothing but good things about them. The people I speak with highly recommend them.

Posted by: Jack | Jan 1, 2007 3:28:06 AM

The electrical efficiency of an on-demand unit is much better than a conventional water heater, but with the price of electricity only around 12-cents per kWH here in Texas, the cost difference is hardly justified.

I am curious about your question of Shabbat violation. It never occurred to me that using such an automated system might be a problem.

Posted by: Bob | Jan 1, 2007 5:41:41 AM

One of the problems with using hot water on Shabbat is that most systems work by the cold water flowing in to replace the water going out, and the cold water gets cooked when that happens. I know several poskim that turn off the heater before shabbat so the water is no longer yad soledet bo, at which point they can use it at will. But it won't be that hot anymore, of course, and will take time to recycle motzei Shabbat.

Posted by: Barzilai | Jan 1, 2007 7:44:25 AM

Judy... Our area of Gush Etzion is probably comparable to England (although with out all that rain). Thanks.

Katherine... Thanks, I'm hearing a lot of the 'instant gratification' ting from people I ask... but the deal breaker for me will be if we would be able to have it feed into a holding tank so there would be warm water on Shabbat for us to wash dishes with! Details, details! :-)

marallyn... Let me get this straight... you're apologizing to me because you have a life offline? Puleeze! :-) On the point of 'yunkers', out house does not have them (or any other kind of 'central heat', so this would have to be a stand-alone solution.

Jaime... Anteres offered an excellent answer to your question. Basically I'm tired of having to deal with the cranky electric element in the old hot water tank.

mother in Israel... Where did you get your info? My plumber is telling me that the electric element in the tank has to be changed every year or two... and that the solar panels need to be replaced every 10 - 12 years. Something doesn't make sense here! :-)

antares... Thanks for providing the timely explanation. BTW, yet another thing we share... a portion of our past living on a boat! :-)

tnspr569... The trick is to push the button 20 minutes before you jump into the shower! :-)

Maksim-Smelchak... Yikes, that sounded an awful lot like a good-bye. I hope the lack of compelling writing lately hasn't chased you off!

Safranit... I wish our home had been built with preparation for yunkers. To add it at this stage would require use to tear up the floors and walls. :-(

The Misanthrope... Best to you and yours as well.

Jack... 4 out of 5 Dentists? :-)

Bob... I see Barzilia beat me to the explanation. Let me know if you have any other questions.

Barzilia... Thanks for answering Bob. I'm looking into whether it is possible to have the on-demand unit (which can be turned off for shabbat) feed into a holding tank. I'll let you know.

Posted by: treppenwitz | Jan 1, 2007 10:04:35 AM

Hi David,

Not at all... all the best to you and yours and a happy 2007!


Posted by: Maksim-Smelchak | Jan 1, 2007 7:45:28 PM

Jack... 4 out of 5 Dentists? :-)

No, contractors.

Posted by: Jack | Jan 1, 2007 9:03:38 PM

Ok...I'm still a little dense here. We have a hot water heater and furnace that is run by gas (except for the A/C.) We never had to replace an electric element (whatever an "element" is) and as for the temp of the tank, you can adjust that. I don't see why a hot water heater would even be an issue for shabbat since many folks use those electric kitchen gadgets to keep food and beverages warm (unless because its food related that is the difference - but that doesn't make sence either, because if you need hot water for food preparation, can't you just use the hot water from the tap?)

Anyhow...I love learning about home improvement stuff. So sorry for all the inquiry, just curious to know how it works and if I should be more aware of our own water heater. We get our furnace serviced twice a year - heater/ac - don't know if that has anything to do with the hot water heater?

Posted by: jaime | Jan 1, 2007 10:22:45 PM

Tankless water heater

Posted by: Jack | Jan 2, 2007 7:43:19 AM

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