They've been around in this part of the world for many years. In fact just a day or two ago I was looking at an old trade journal dating from 1966, and there was an ad for a 6 to 7kW over-sink unit.
The biggest drawback is that they raise the temperature THROUGH a number of degrees rather than TO an absolute temperature. Output temperature is dependent upon the temperature of the cold water supply and the flow rate, so to get high temperature output the flow rate is generally much lower than with a conventional system. If the cold temperature and supply pressure are fairly constant, the output temperature will be so as well, but the only way to increase the temperature is to reduce the flow rate so that the water is in contact with the heating elements for longer.
These devices are now very popular here in "instant" electric showers where a lower rate of flow is acceptable, but there are one or two units available now to feed normal basin/sink taps (faucets) as well. These are rated up to 9.5 kW, although I have no idea whether you have more powerful units on sale in America.
I'll dig out some temperature/flow data if you're interested.
Re: tankless water heaters#4817 10/19/0108:19 PM10/19/0108:19 PM
Yes those are exactly what they are, however the ones you mention pale in comparison, I got a call from a customer and he wants to get one but he is talking two 50 amp breakers feeding the thing. The liturture he has talks about 18 kw to 22 kw, I mean these are some large units for a residence. Also, the ccost is between $650 to $750 per unit. Plus with deregulation I would wonder if it would really be worth the investment. From what I have read they are the size of a phone Book, there is no storage capacity, it just heats the water like right now, and the temp depends on the flow rate and incoming water temp. which makes sense. Yes if you got some charts it would be interesting to see them. Thanks for the quick reply.
Re: tankless water heaters#4819 10/20/0104:43 AM10/20/0104:43 AM
Wow, 18 to 22kW! That makes my old 6kW shower unit seem like a weakling! Those sort of figures sound more like the equivalent power output of the gas-fired "multi-point" heaters like Tom described.
Here's sthe manufacturer's data for the British Triton TW10i, recommended for up to 2 outlets. I've converted the metric & centigrade measurements to U.S. units, hence the non-round flow figures:
Power: Selectable 6kW or 9.5kW Dimensions: 7.1 x 11.6 x 3.4 inches * Water in at 50 deg. F, 9.5kW setting: 0.53 U.S. gal/min., 158 F. 0.79 U.S. gal/min., 133 F. 1.06 U.S. gal/min., 111 F. * Water in at 77 deg. F, 9.5kW setting: 0.53 U.S. gal/min., 185 F. 0.79 U.S. gal/min., 160 F. 1.06 U.S. gal/min., 138 F. * Water in at 77 deg. F, 6kW setting: 0.53 U.S. gal/min., 167 F. 0.79 U.S. gal/min., 138 F. 1.06 U.S. gal/min., 120 F. * The cost of this unit by cmparison is £122.50 (about $180) plus tax.
Re: tankless water heaters#4820 10/20/0110:37 AM10/20/0110:37 AM
Bill: The company I believe is ' SETS systems ',their E-mail is Tankless-water-heater.com they have the heads youre thinking about. As Paulik pointed out rate of flow is key to a high rise in temperature, they assume incoming water temperature to be minimun of 50 degrees F and at optimum flow rate a rise of I think it said 66 degrees, but and supposedly that 50 degrees was an average for the worst case. This I find hard to believe especially in northern climates where older homes do not heat their basements and the outside temps drop as low as -5 to -15 degrees below zero. and in basements where the pipes get cold enough to freeze and dont because of the basement is kept at about 40-45 degrees, any way the rise will not reach the optimum temp. To All: IMO a 22kw Electrical heating unit is just plain bad planning. If a customer has Central Air, electric Range, Dryer,some small appliances ie disposer, dishwasher etc and then adds a 22 kw tankless the combined load is over 200 amps. I like Tom's idea of a gas fired one seems a lot more economical that a 22kw electric model/ this model and a few others of less power still require two 50 amp breakers, and the manufactureer could not guarantee that the circuit only drew 80 amps, or 75 for a smaller model. The smaller models as Paulik was talking about sound much more practical.