Tankless Water Heater

Have one in my flat - lived here for about 3 years. No problems - works fine. Gets a bit chilly in the shower when the CH is on full blast, but you can kill the heating for 10 minutes while you shower, then put it back on.

A bit bigger boiler would probably have sorted that, but I'm at my Landlord's mercy.

I have a 6-room flat, incl. kitchen & bathroom. Radiator in each room. (1st floor of a terraced house + loft converion (my office/workshop)). It's a gas combi-boiler (as they're known around here), 24kW. I wouldn't want anything smaller; as I said, it's a bit on the edge for CH + shower. There's never any problem with getting a bath full of scalding water in a reasonable time, when it's needed.

Have to say, the insulation could be a lot better - where I work freezes in winter (without loads of heating on) and boils in summer.

I live mostly alone, my daughter stays 3 days/nights per week.

Gas bills average £25 pcm. (Gas for CH/HW only. Electric cooker etc.)

my in-laws replaced a 50 gallon tank with a tankless one rated to equal and it has lowered their gas use and they never run out on that line but the other side of the house does run short.

Seems to be the most common type of residential heater in India. Also Thailand and many other places. There is typically a small wall mounted electric unit, barely enough to take a shower, but effective. Some looked very nice and included a hose and shower head. These did not even run until water was flowing, so there was zero cost unless used. Also have used a whole house style system from Germany that was gas fired. It could keep up with normal hot water use indefinitely, but did have the problem that small flow rates would not be sensed to start the heater.

I travel to Central America and East Africa frequently and am familiar with the in-line units you speak of for showers. They work fine, but I (and a number of my friends) have serious concerns over the safety of this type of unit.

We do not use the electric for showers or baths, thats covered by a gas fired unit. We only use the electric for hot water for hand washing....

What are your concerns?

Is this for your house or a plant somewhere? I think you probably have the answers if it's a house, but if it is something like an instantaneous jet heater in a plant there are pros and cons. The pro is that if set up correctly they are efficient, quiet and will be able to give you instantaneous hot water with very few loses. Cons are that if not set up right they can cause significant hammer, and as they are continuous flow devices, are often harder to control that a simple tank system.

I guess that I have also assumed that you are adding steam directly into your process fluid, a jacketed pipe solves potential problems with adding steam into the process fluid.

Go for it. You'll be glad you did. Remember water is colder in winter so it has has to have enough capacity to make that water hot. By a bigger size than you think you need. You'll be happier and still save a bundle.

Sometimes they are called 'instant water heater'. They have numerous applications in washrooms, where the demand for hot water is intermittent and the run from any location where a storage tank might be placed is long; otherwise a pipe-full of cold water would be run to waste long before the hot water arrived.

Many people have this arrangement in the form of 'power showers', where the water for showering is heated in a unit installed within the shower enclosure only when the shower is running. Such an arrangement obviates the need to heat water and maintain it stored hot within the building.

Each unit has a pressure relief device installed. In the event of the outlet becoming blocked the relief device will operate, maintaining the flow through the unit that cools the element and prevents it burning out. In the case of a shower assembly, the spray nozzles need to be kept clear of limescale that might cause blockages, by partial dismantling and mechanical or chemical cleaning. Provided this takes place at intervals, then these units are agreeable in terms of effectiveness and thermal economy. They have a lot going for them in the right application.

There are electric and gas versions. Our gas central heating switches over to water heating each time hot water is drawn, no storage. It works great, but make sure that you have at least 24KW of heating energy if you want a shower that really has a good mass of water (I hate those UK electric shower "things" that do not get you wet until you have been under them 10 minutes!).

I have a small house and 18kw would heat the house, but water throughput when bathing or showering was too low. So when I replaced, I went to 27kw (against all advice) it cost a little more, only incidental money, but I am REALLY HAPPY. Lots of hot water and the heating goes from stone cold to noticeably warmer in about 4 minutes in any room!!! That is now 10 years on.....

I used a propane one on my boat for 12 years, no problems.

Had hot water for as long as the tap was turned on.

It only works when you open the tap.

Great things.

We never had anything else than tankless heaters in Holland. The big difference between low end and high end is the capacity to heat fast enough for large water consumption such as showers. We had one that was rated to 250 ltrs/min and was superb. Sorry don't know the Kw ratings but maybe somebody else can convert this.

We had combined central heating and hot water but they also do smaller ones for just the hot water. Most now have an efficiency so high that you could not do the same with electrical or even with a tank storage system linked via your central heating unless you have one of these super duper new ones.

There are electrical ones around for where you cannot get a hot supply to, or it is simply to far to be worthwhile, I have recently fitted two different models from the same company, the small single phase one is OK for hand washing etc., the larger 2 phase of a 3 phase supply and 4.3 KW is not bad, makes water quite hot after a few seconds.

They are better than keeping a gallon of water hot all year round with the subsequent losses, according to an ad, they pay for themselves in about the first year in most situations....

Also, they stop the whole big gas boiler heating up unnecessarily in the summer, just to wash your hands....

I use a tankless electric water heater in my apartment.

here it is:

http://www.heater-store.com/stiebel-eltron-dhc-10-2-tankless-electric-water-heater_589_prd1.htm

It works well but my plumbing had be designed for it.

First off I have a well so the pressure fluctuates. This is a problem I overcame by putting in a water pressure regulator where the water main enters the apartment and set it just a tad lower than the min pressure before the pump kicks on.

Unlike a regular water heater, these things just kick on at a certain flow rate. The faster the flow the less it heats. So if you want really hot water, you crack the hot water handle just enough to activate the heater. My faucets and showers have to have independant hot and cold valves because the single handle type (way more common) do not provide for independant hot and cold throttling capability.

All this said, you must realize, I am a cheap bastard so I bought the cheapest one I could find. Maybe some of the more expensive and sophisticated ones don't present the same challanges.

The coolest thing about them is how tiny they are.

Good luck.

My only problem with this (my parents have a similar device, but gas) is having to turn the water on lots to avoid scalds. This year, it's been pretty damn wet here (lots of people flooded out in parts of the UK), but in the past few years we've been bombarded with messages about saving water. It seems the world needs more water. Tell it to the folks in Tabasco.

My system seems to overcome the problem of superheated steam coming out at low flow rates (don't know how), but as I'm also "a cheap bastard" I resent having to refill the 'dead leg' (plumbing term ) of pipe from the boiler to the tap. When I turn the tap off, all that lovely hot water (heated indirectly by the sweat of my brow) will sit in the pipes doing nothing useful.

The formerly ubiquitous Ascot gas fired water heaters got around the 'dead leg' problem by siting the heater directly over the sink. Problems included poor control of water temperature, intrusive siting (a big lump of heater over the sink) & high probability of CO emission (usually due to bad installation practice). This type of water heater seems to have largely died out around here.

You wrote a couple of points that maybe I can help you with:-

My only problem with this (my parents have a similar device, but gas) is having to turn the water on lots to avoid scalds.

You need a special mixer tap that is temperature controlled. The reason that I bought it was that without it and somebody uses water elsewhere, you got water that was suddenly too hot or too cold. The mixer actually allows the boiler to cycle between high, medium, low and off and you do not notice the temperature changes at all, brilliant!! It evens them out spectacularly.....

Be careful, there are basically two different types, only one is correct for such a boiler, do not ask me why, I have forgotten.

When I turn the tap off, all that lovely hot water (heated indirectly by the sweat of my brow) will sit in the pipes doing nothing useful.

Two things, if pressure is good, reduce the size of the pipe and insulate it well. You are still saving money over a hot tank system and reducing your exposure to possible Legionnaire's Desease....

This type of water heater seems to have largely died out around here.

Maybe the people died of CO poisoning!! Today you must vent to outside and the controls work a lot better I find with regards to temperature, though I have not used one in years....they have surely just got even better since then.....! Hopefully!!

My parents' house had a Ruud gas unit when I was a child, probably dated from the 1930's. It occasionally had problems with not cutting off when the water was shut off. Never had problems with too little hot water.

Nobody has raised the issue of electrical demand. In many areas, the electric utility gets hit with a peak demand in summer evenings, just after people return home from work. If they don't have significant load-shedding programs in place, the utility has to have back-up peaking power generation equipment which is needed only for a relatively small percent of a year's time. This is capital equipment cost which translates into higher bills, etc. An electrically operated tankless unit will just add one more electrical load to the system, and it is likely to be in use during this same time of peak usage. You are trading one type of problem for another.

Lots of options exist to address this concern. So, instead of "blindly" advocating the tankless approach, lets include some "intelligent design". Look at the whole environment in a home or business; expand this to look at peak load problems for the utility as well as time of day metering and other metering methods which can adjust billing rates and connected load to react to peak load conditions. Look at the times when insulating the storage tank to R-60 (which has a payback less than 1-year) is do-able.

Thimk! -JMM

I love you sign off - THIMK!!

Something new.

I feel the only real answer is to go Solar as much as possible and

a) store the heat

b) use a heat pump to boost it up....

I want to "play" when I retire.....

4 as I am aware of:

1. Electrical as Capt Psycho

2 . If steam/ hot water is available - a 3 way temp.control mixing valve. For Hot + Cold = Reqd. Water temp. controlled by the sensor.

3 . Direct-gas fired with thermostat to on/off burner & keep pilot open.\

4 . Thankless water heater - A coiled electrical heater with thermostat on knob.You take bucket of water and dip in the coil, the hook on the knob sticks to the brim of the bucket. Water gets hot, remove heater take a mug, squat & take bath.