We live in a very old house with bad plumbing. The 50 gal. hot water tank in the basement is connected to the kitchen sink by such a lengthy, labyrinthine course of pipe that it takes forever (> 10 minutes) just to go from cold to lukewarm. Running a new pipe connection is not really an option. (Hot water to the rest of the house is satisfactory.)

So I'm wondering about under-sink heaters that take cold water and produce hot water electrically on demand. Additional info that might be relevant:

• Besides a hot water faucet there are two dishwashers flanking the sink.
• We have city water that's fairly hard.
• If there isn't room under the sink I can easily install it under the kitchen floor below the sink.
• It's a short electrical run to the circuit breaker box.

Questions:

• Will this work?
• Do you connect the input to hot water or cold?
• Does is require 120 or 240 Volts?
• Does it produce hot water at a constant, user-set temperature?

Has anyone used one of these in their kitchen?
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02-25-07, 07:17 PM
babthrower
(Have you tried insulating the pipes with foam tubing to see if that makes enough difference to solve the problem? I've done it, it's really easy.)

02-25-07, 07:33 PM
coldfuse

quote:
Originally posted by Professor:
Questions:

* Will this work?
* Do you connect the input to hot water or cold?
* Does is require 120 or 240 Volts?
* Does it produce hot water at a constant, user-set temperature?

Has anyone used one of these in their kitchen?



This sounds like an excellent solution for your problem. The Mrs. teaches about tankless water heaters in her product knowledge class, and one is on our list of projects for the coming year. I have successfully applied them in the past on machinery used to test heat exchanger performance. As for your questions:

* It may be a good enough idea that you ultimately replaced your tank with another.

* The input is connected to cold water. Depending on manufacturer you may expect a possible temperature rise of 70 to 90 degrees Fahrenheit or so.

* Check your selected product for voltage. One I am considering is 120V, coming standard with a 1500 W element requiring a 20 amp breaker. Alternatively, gas and propane models are available but may be more expensive to purchase and install. Look for tax credit opportunities.

* Some models even come with a remote control to set the temperature!

You will want to be careful with the temperature setting. The one I used for the test machinery had the capacity to become a steam boiler, which of course the residential models are protected against.

Good luck with your project. Let me know of the pitfalls before I start mine Big Grin

02-27-07, 02:41 AM
Professor
Thanks to you both for replying.

babs, I've insulated a few horizontal runs already as you desribed. But the pipes are impossible to follow, disappearing and reappearing within the basement walls. I think the hot water goes up to the 2nd floor before returning to the basement in its tenacious quest to find my kitchen sink, possibly touring the attic in the process Smile Most of the runs are 1/2" but some are smaller, with many elbows, tees, and valves -- high resistance & high heat loss. Time for a change.

'fuse, thanks for the info. 'Tankless water heater' is the magic phrase I was searching for. 70-90F temp rise sounds like it might not reach dishwasher temperature, but there's an 'added heat' setting on the dishwashers. I'll read up on what products are available.

Remote control? Roll Eyes

02-27-07, 09:43 AM
coldfuse
Prof, your dishwasher may take in cold water and heat it to dishwasher temperatures already!

02-27-07, 10:26 PM
Professor
That's true if the water supply isn't too cold -- at least the dishwashers heat up enough now. But my main concern is that the hot water faucet in a kitchen should promptly deliver hot water. Even *I* have been known to do a few dishes by hand now and then. Smile

02-28-07, 12:09 PM
aminator2002
You could also consider adding a recirculation line to the kitchen sink. This involves adding an additional line back to the area of the heater and then a small pump. It can be more economical in some instances.

Probably in an old house this isn't an easy solution so the small tank is probably the best bet. Be cautious of your tank under the sink though, they are notorious for developing leaks. It might not leak at first but the tanks seem to have small inlets and outlets that are more prone to leaks than other plumbing fixtures. Keep an eye on it because I can't tell you how many moldy disgusting sink cabinets I've seen over the years.

03-01-07, 02:07 AM
Professor
thanks, ami. Somebody else suggested a recirculating system for this application, too. I thought those were just found in big hotels.

If I install a small tank for just the kitchen, a perfect location would be the space under the floor -- to catch drips and fix leaks. I agree about keeping cabinets under sinks bone-dry.

I re-examined the phsyical relationship between the hot water tank and the kitchen floor under the sink. A straight shot would take about 50 feet of pipe, most of it in one long horizontal run under and over and through various obstructions along the basement ceiling.

With 3/4" pipe or bigger, I think that would solve the problem without the need for another tank, recirculator, or added heat. I would try to leave enough clearance for the foam insulators babs described.

I know I said that "running a new pipe connection is not really an option", but I changed my mind. Red Face It's starting to seem like the most sensible option indeed, and -- forgive the pun -- it's the path of least resistance. Big Grin

Of course, I never would have come to this realization without talking it over with you guys on AP. Funny how that works. Smile

03-01-07, 05:50 PM
aminator2002
50 feet of pipe with bends may leave you with the same problem but improved. I'd predict about 2 and a half minutes of wait time. 3/4 pipe may make it less but lots of bends reduces the effective size of pipe.

Maybe you should track down the calculations... figuring the bends and all.

I primarily work on high rises and we find recirc lines very helpful. You don't even have to put a pump necessarily... just a return line sometimes helps.

If you're doing the work yourself then just do some progress checks and see how it goes. You might want to look at putting the pipe against an interior wall at a single height to avoid ups and downs... this will help a bit with the flow loss from elbows.

Or maybe just try first using the new line as a recirc line... tap onto the old line and see what happens when a recirc line is added.

Hmm... maybe I'm just confusing matters. Wink

03-01-07, 07:51 PM
Professor
My previous post was misleading -- by "one long horizontal run under and over and through various obstructions along the basement ceiling" I meant literally a length of straight pipe. I see a clear path running above and below existing pipes, conduits, and ducts (the new pipe would have to be hung 6-8" below the finished ceiling). The only drilling required would be through walls above two door jambs.

Re foam insulation for hot water pipes: Seems to me it wouldn't speed the wait time to reach full hot, but it would allow a somewhat higher final temperature due to lower heat loss during flow. I'm assuming that the sink is used infrequently, so whenever the faucet is opened the hot water in the pipes is cold, even with insulation.

ami, we have a hot-water radiator system that passively recirculates by convection, and I would think the same principle applies to the high rises you work on. In the case of my kitchen, the faucet and tank are only slightly separated in height, so I'd need a pump, right?

After running a new hot water supply I would close off the old one for good. If I'm going to experiment with recirculation I'd probably run a 2nd parallel line. It just sounds like a lot of trouble to improve the wait time for hot water from, say, 30 seconds to 3 seconds. Now if I were building a new house... Smile

03-01-07, 08:58 PM
aminator2002
You are right about the insulation. The easiest insulation to use is fiberglass insulation with white paper outer layer that has masking tape attached to it. This is the proper insulation to use for plumbing lines... the black foam kind is typically for AC lines. (I think you could use the black foam style, but it's no easier to use from what I have seen. In any event, we don't usually insulate the hot except at risers and long runs. The only benefit is that the hot water in the line would maintain temperature between intermittent uses so you'd get warm water immediately after up to a couple hours.

I can't honestly tell you much about the passive recirculation. We use active recirculation with recirc lines and pumps which then is regulated using flow restrictors - we actually dial up how many gallons a minute get recirc'ed, but if your line is straight without bends then you should be making a huge improvement just with running a new 3/4" line. To clear a straight line of 3/4" running 50 feet it might take 25 seconds or so depending on your pressure. I think that's a pretty normal wait time and not in the range of annoying... anything over a minute is pretty irritating.

Pumps are pretty inexpensive and can be installed after the fact if your new line doesn't deliver the results you want. Just leave that insulation off until you've tested it.

The more I think about it, the more I think you should plan to insulate so remember to leave room around your pipe. The insulation is a lot bigger than the pipe itself.

By the way, a new study indicates that washing dishes in cool water can be just as effective as using hot water if you use an antimicrobial rinse. (just heard that yesterday) Wink

03-02-07, 11:04 AM
Professor
I don't recall ever seeing the pipe insulation you are describing. Would they sell it at places like Home Depot or Lowe's?

Our dishwashers have a so-called "anti bacteria" setting -- it's the longest duration cycle available. Does that mean the rinse water is hotter, or are the heating coils doing overtime while drying the dishes, or what? User's manuals never explain how things work. Mad

quote:
Originally posted by coldfuse:
The Mrs. teaches about tankless water heaters in her product knowledge class, and one is on our list of projects for the coming year.

I'd love to hear more about it. I still haven't really done my homework yet. I may have been hasty in considering a tankless water heater for my kitchen to be the ideal solution to the problem, but I can think of other places in the house where it might be perfect.

Are tankless systems gaining in popularity? Commercial vs. residential?

03-02-07, 11:06 AM
Professor
Are there tankless systems that could warm our bath water for only the first 2-3 minutes until the pipes heat up, then shut off?

03-02-07, 01:29 PM
coldfuse
An expensive control valving arrangement might accomplish such a feat, but where would the water from your tank flow to warm up while this was going on? Part of the beauty of a tankless water heater is not having to re-heat the water in the tank.

03-02-07, 03:18 PM
Professor
Fuse, there's no beauty to be found in the plumbing of my old house. Big Grin Actually re-heating the water is exactly what I had in mind all along. Not so much a replacement as a "booster" for the tank supply at that one particular faucet.

Doesn't a tankless heater have switchable heat that can be shut off above a certain temp? I'd be willing to rig up a temp sensor to a heater relay, as long as my family doesn't have to look at it...

03-08-07, 10:50 AM
DvdGStwrt
We have a 20 gallon under sink electric water heater that serves both bath and kitchen (We live in a trailer, the common wall between the two rooms has the plumbing).

With 20 gallons of hot water we can take showers, do the dishes and fill the tub half way with "warm" water. It is a two part process to fill the tub completely.

Under sink water tanks run from 10 to 20 gallons - more than enough to do dishes, run a dish washer.

The new models are highly energy efficient - When the power went out for a day we still had hot water 5 hours down the road coming from the tank (granted due to no pump the water flow was a trickle).

We considered the option of "on demand" hot water but was talked out of it by the store clerk who claimed that many complaints were made when it comes to the energy bill.

I would talk with a plumber or a dealership (mostly the plumber) to find out which is best for you.

03-09-07, 03:58 PM
Professor
Thanks, D. I don't think I could fit 20 gallons under my sink -- I'm not even sure about 10, though it would easily go into that basement space under the kitchen floor. That would certainly eliminate any remaining time delay associated with a new pipe run, and could be set to a higher temp than the main water heater.

The cost of electricity is not a main concern in this case -- electric power rates are relatively low in our locality. (Unfortunately we get eaten alive on heating costs -- the radiator system is fueled with heating oil -- very expen$ive.)

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